Immunodiagnostic Studies

OVERVIEW OF IMMUNODIAGNOSTIC STUDIES

Immunodiagnostic or serodiagnostic testing studies antigen-antibody reactions for diagnosis of infectious disease, autoimmune disorders, immune allergies, and neoplastic disease. These modalities also test for blood groups and types, tissue and graft transplant matching, and cellular immunology. Blood serum is tested for antibodies against particular antigens—hence the term blood serology testing.

Antigens are substances that stimulate and subsequently react with the products of an immune response. They may be enzymes, toxins, microorganisms (e.g., bacterial, viral, parasitic, fungal), tumors, or autoimmune factors. Antibodies are proteins produced by the body’s immune system in response to an antigen or antigens. The antigen-antibody response is the body’s natural defense against invading organisms. Red blood cell groups contain almost 400 antigens. Immune reactions to these antigens result in a wide variety of clinical disorders, which can be tested (e.g., Coombs’ test).

Pathologically, autoimmune disorders are produced by autoantibodies—that is, antibodies against self. Examples include systemic rheumatic diseases, such as rheumatoid arthritis and lupus erythematosus.

Immunodeficiency diseases exhibit a lack of one or more basic components of the immune system, which includes B lymphocytes, T lymphocytes, phagocytic cells, and the complement system. These diseases are classified as primary (e.g., congenital, DiGeorge syndrome) and secondary (e.g., acquired immunodeficiency syndrome [AIDS]).

Hypersensitivity reactions are documented using immediate hypersensitivity tests and are defined as abnormally increased immune responses to some allergens (e.g., allergic reaction to bee stings or pollens). Delayed hypersensitivity skin tests are commonly used to evaluate cellmediated immunity. Histocompatibility antigens (transplantation antigens) and tests for human leukocyte antigen (HLA) are important diagnostic tools to detect and prevent immune rejection in transplantation.

Types of Tests

Many methods of varying sophistication are used for immunodiagnostic studies (Table 8.1).

Collection of Serum for Immunologic Tests

Specific antibodies can be detected in serum and other body fluids (e.g., synovial fluid, CSF).

1. Procure samples. For diagnosis of infectious disease, a blood sample (serum preferred) using a 7-mL red-topped tube should be obtained at illness onset (acute phase), and the other sample should be drawn 3 to 4 weeks later (convalescent phase). In general, serologic test usefulness depends on a titer increase in the time interval between the acute and the convalescent phase. For some serologic tests, one serum sample may be adequate if the antibody presence indicates an abnormal condition or the antibody titer is unusually high. See Appendix A for standard precautions.

2. Perform the serologic test before doing skin testing. Skin testing often induces antibody production and could interfere with serologic test results.

3. Label the sample properly and submit requested information. Place specimen in biohazard bag. Send samples to the laboratory promptly. Hemolyzed samples cannot yield accurate results. Hemoglobin in the serum sample can interfere with complement-fixing antibody values.

Interpreting Results of Immunologic Tests

The following factors affect test results:

1. History of previous infection by the same organism

2. Previous vaccination (determine time frame)

3. Anamnestic reactions caused by heterologous antigens: An anamnestic reaction is the appearance of antibodies in the blood after administration of an antigen to which the patient has previously developed a primary immune response.

4. Cross-reactivity: Antibodies produced by one species of an organism can react with an entirely different species (e.g., Tularemia antibodies may agglutinate Brucella and vice versa, rickettsial infections may produce antibodies reactive with Proteus OX19).

5. Presence of other serious illness states (e.g., lack of immunologic response in agammaglobulinemia, cancer treatment with immunosuppressant drugs)

6. Seroconversion: the detection of specific antibody in the serum of an individual when this antibody was previously undetectable

TABLE 8.1 Some Tests That Determine Antigen-Antibody Reactions

Name of Test	Observable Reaction	Visible Change	Tests for
Agglutination, hemagglutination (HA), immune hemagglutination assay (IHA)	Particulate antigen reacts with corresponding antibody; antigen may be in form of RBCs (hemagglutination, latex, or charcoal coated with antigen).	Clumping	Treponemal, heterophile, and cold agglutinin antibodies
Precipitation (e.g., immunodiffusion [ID], counterimmunoelectrophoresis [CIE])	Soluble antigen reacts with corresponding antibody by ID or count.	Precipitates	Fungal antibodies, food poisoning
Complement fixation (CF)	Competition between two antigen-antibody systems (test and indicator systems)	Complement activation, hemolysis	Viral antibodies
Immunofluorescence (e.g., indirect fluorescent antibody [IFA])	Fluorescenttagged antibody reacts with antigen-antibody complex in the presence of ultraviolet light.	Visible microscopic fluorescence	Antinuclear antibodies (ANAs); antimitochondrial antibodies (AMAs)
Enzyme immunoassay (EIA)	Enzymes are used to label induced antigen-antibody reactions.	Chromogenic fluorescent or luminescent change in substrate	Hepatitis and human immunodeficiency virus (HIV) (screening)
Enzyme-linked immunosorbent assay (ELISA)	Indirect EIA for quantification of an antigen or antibody enzyme and substrate	Color change indicates enzyme substrate reaction.	Lyme disease, Epstein-Barr virus, extractable nuclear antibodies (connective tissue/systemic rheumatic disease)
Immunoblot (e.g., Western blot [WB])	Electrophoresis separation of antigen subspecies	Detection of antibodies of specific mobility	Confirms HIV-1
Polymerase chain reaction (PCR)	Amplifies low levels of specific DNA sequences; each cycle doubles the amount of specific DNA sequence.	Exponential accumulation of DNA fragment being amplified; defects in DNA appear as mutations.	Slightest trace of infection can be detected; more accurate than traditional tests for chlamydia; genetic disorders
Rate nephelometry	Measures either antigen or antibody in solution through the scattering of a light beam; antibody reagent used to detect antigen IgA, IgG, IgM; concurrent controls are run to establish amount of background scatter in reagents and test samples.	Light scatter proportionately increases as numbered size of immune complexes increases.	Quantitative immunoglobulins IgA, IgM, C-reactive protein, antistreptolysin O recorded in mg/dL or IU/mL
Flow cytometry	Blood cell types are identified with monoclonal antibodies (mABs) specific for cell markers by means of a flow cytometer with an argon laser beam; as the cells pass the beam, they scatter the light; light energy is converted into electrical energy cells and stained with green (fluorescence) or orange (phytoerythrin).	Light scatter identifies cell size and granularity of lymphocytes, monocytes, and granulocytes; color fluorochromes tagged to monoclonal antibodies bind to specific surface antigens for simultaneous detection of lymphocyte subsets.	Lymphocyte immunophenocytology differentiates B cells from T cells and T-helper cells from T-suppressor cells.
Restriction fragment length polymorphism (RFLP)	DNA-based typing technique		Epidemiology of nosocomial and communityacquired infections
cDNA probes	Uses cDNA probes directed against ribosomal RNA	Amplifies nucleic acid to identify presence of bacterial or viral load	Infectious disease such as tuberculosis, hepatitis C virus, and HIV

Serologic Versus Microbiologic Methods

Serologic testing for microbial immunology evaluates the presence of antibodies produced by antigens of bacteria, viruses, fungi, and parasites. The best means of establishing infectious disease etiology is by isolation and confirmation of the involved pathogen. Serologic methods can assist or confirm microbiologic analysis when the patient is tested late in the disease course, antimicrobial therapy has suppressed organism growth, or culture methods cannot verify a causative agent.

BACTERIAL TESTS

Syphilis Detection Tests

Syphilis is a venereal disease caused by Treponema pallidum, a spirochete with closely wound coils approximately 8 to 15 µm long. Untreated, the disease progresses through three stages that can extend over many years.

Antibodies to syphilis begin to appear in the blood 4 to 6 weeks after infection (Table 8.2). Nontreponemal tests determine the presence of reagin, which is a nontreponemal autoantibody directed against cardiolipin antigens. These tests include the rapid plasma reagin (RPR) and Venereal Disease Research Laboratory (VDRL) tests. The U.S. Centers for Disease Control and Prevention (CDC) recommend these tests for syphilis screening; however, they may show negative results in some cases of late syphilis. Biologic false-positive results can also occur (Table 8.3).

Conversely, treponemal (i.e., specific) tests detect antibodies to T. pallidum. These tests include the passive particle agglutination T. pallidum test (TP-PA) and the fluorescent treponemal antibody absorption test (FTA-ABS). These tests confirm syphilis when a positive nontreponemal test result is obtained. Because these tests are more complex, they are not used for screening. Certain states require automatic confirmation for all reactive screening tests by using a treponemal test such as the TP-PA or FTA-ABS.

Reference Values

Normal

Nonreactive, negative for syphilis

TABLE 8.2 Sensitivity of Commonly Used Serologic Tests for Syphilis

Test	Stage
Test	Primary (%)	Secondary (%)	Late (%)
Nontreponemal (Reagin) Tests
Venereal Disease Research Laboratory test (VDRL)	70	99	1^*
Rapid plasma reagin card test (RPR); automated reagin test (ART)	80	99	0
Specific Treponemal Tests
Fluorescent treponemal antibody absorption test (FTA-ABS)	85	100	98
Treponema pallidum particle agglutination (TP-PA)	65	100	95
(This new procedure has sensitivity similar to MHA-TP.)
^**Treated late syphilis.
Modified from Tramont EC: Treponema pallidum. In Mandell GI, Douglas RE, Bennett JE (eds): Principles and Practice of Infectious Diseases.
New York, John Wiley & Sons, 1985, p. 1329. Also product insert Serodia TP-PA, Fujirebio, Inc., Tokyo, Japan, 2000.

TABLE 8.3 Nonsyphilitic Conditions Giving Biologic False-Positive Results (BFPs) Using VDRL and RPR Tests

Disease	Approximate Percentage BFPs
Malaria	100
Leprosy	60
Relapsing fever	30
Active immunization in children	20
Infectious mononucleosis	20
Lupus erythematosus	20
Lymphogranuloma venereum	20
Pneumonia, atypical	20
Rat-bite fever	20
Typhus fever	20
Vaccinia	20
Infectious hepatitis	10
Leptospirosis (Weil’s disease)	10
Periarteritis nodosa	10
Trypanosomiasis	10
Chancroid	5
Chickenpox	5
Measles	5
Rheumatoid arthritis	5-7
Rheumatic fever	5-6
Scarlet fever	5
Subacute bacterial endocarditis	5
Pneumonia, pneumococcal	3-5
Tuberculosis, advanced pulmonary	3-5
Blood loss, repeated	? (low)
Common cold	? (low)
Pregnancy	? (low)

Sensitivity of FTA-ABS

Primary syphilis: 84% Secondary syphilis: 100% Latent syphilis: 100% Late syphilis: 96%

Sensitivity of TP-PA

Primary syphilis: 86% Secondary syphilis: 100% Latent syphilis: 100%

Procedure

1. Collect a 7-mL blood serum sample in a red-topped tube. Observe standard precautions. Fasting is usually not required.

2. Place specimen in a biohazard bag for transport to the laboratory.

Clinical Implications

Diagnosis of syphilis requires correlation of patient history, physical findings, and results of syphilis antibody tests. T. pallidum is diagnosed when both the screening and the confirmatory tests are reactive.
Treatment of syphilis may alter both the clinical course and the serologic pattern of the disease. Treatment related to tests that measure reagin (RPR and VDRL) includes the following measures:
- If the patient is treated at the seronegative primary stage (e.g., after the appearance of the syphilitic chancre but before the appearance of reaction or reagin), the VDRL remains nonreactive.
- If the patient is treated in the seropositive primary stage (e.g., after the appearance of a reaction), the VDRL usually becomes nonreactive within 6 months of treatment.
- If the patient is treated during the secondary stage, the VDRL usually becomes nonreactive within 12 to 18 months.
- If the patient is treated >10 years after the disease onset, the VDRL usually remains unchanged.
A negative serologic test may indicate one of the following circumstances:
- The patient does not have syphilis.
- The infection is too recent for antibodies to be produced. Repeat tests should be performed at 1-week, 1-month, and 3-month intervals to establish the presence or absence of disease.
- The syphilis is in a latent or inactive phase.
- The patient has a faulty immunodefense mechanism.
- Laboratory techniques were faulty.

False-Positive and False-Negative Reactions

A positive reaction is not conclusive for syphilis. Several conditions produce biologic false-positive results for syphilis. Biologic false-positive reactions are by no means “false.” They may reveal the presence of other serious diseases. It is theorized that reagin (reaction) is an antibody against tissue lipids. Lipids are presumed to be liberated from body tissue in the normal course of activity. These liberated lipids may then induce antibody formation. Nontreponemal biologic false-positive reactions can occur in the presence of drug abuse, lupus erythematosus, mononucleosis, malaria, leprosy, viral pneumonia, recent immunization, or, on rare occasions, pregnancy. False-negative reactions may occur early in the disease course or during inactive or later stages of disease.

Interfering Factors

Hemolysis can cause false-positive results.
Hepatitis can result in a false-positive test.
Testing too soon after exposure can result in a false-negative test.

Interventions

Pretest Patient Care

Explain test purpose and procedure. Assess for interfering factors. Instruct the patient to abstain from alcohol for at least 24 hours before the blood sample is drawn.
Follow guidelines in Chapter 1 regarding safe, effective, informed pretest care.

Posttest Patient Care

Interpret test results and counsel appropriately. Explain biologic false-positive or false-negative reactions. Advise that repeat testing may be necessary.
Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Lyme Disease Tests

Lyme disease is a multisystem disorder caused by the spirochete Borrelia burgdorferi. It is transmitted by the bite of tiny deer ticks, which reside on deer and other wild animals. Lyme disease is present worldwide, but certain geographic areas show higher incidences. Transmission to humans is highest during the spring, summer, and early fall months. The tick bite usually produces a characteristic rash, termed erythema chronicum migrans. If untreated, sequelae lead to serious joint, cardiac, and central nervous system (CNS) symptoms.

Serologic testing for antibodies to Lyme disease includes enzyme-linked immunosorbent assay (ELISA) and Western blot analysis. Antibody formation takes place in the following manner: Immunoglobulin M (IgM) is detected 3 to 4 weeks after Lyme disease onset, peaks at 6 to 8 weeks after onset, and then gradually disappears. IgG is detected 2 to 3 months after infection and may remain elevated for years. Current CDC recommendations for the serologic diagnosis of Lyme disease are to screen with a polyvalent ELISA (IgG and IgM) and to perform supplemental testing (Western blot) on all equivocal and positive ELISA results.

Western blot assays for antibodies to B. burgdorferi are supplemental rather than confirmatory because their specificity is less than optimal, particularly for detecting IgM. Two-step positive results provide supportive evidence of exposure to B. burgdorferi, which could support a clinical diagnosis of Lyme disease but should not be used as a criterion for diagnosis.

Reference Values

Normal

Negative for both IgG and IgM Lyme antibodies by ELISA and Western blot

Clinical Implications

Ten proteins are useful in the serodiagnosis of Lyme disease. Positive blots are:
- IgM: two of three of the following bands: 21/25, 39, and 41
- IgG: five of the following bands: 18, 21/25, 28, 30, 39, 41, 45, 58, 66, and 93
Serologic tests lack the degree of sensitivity, specificity, and standardization necessary for diagnosis in the absence of clinical history. The antigen detection assay for bacterial proteins is of limited value in early stages of disease.
In patients presenting with a clinical picture of Lyme disease, negative serologic tests are inconclusive during the first month of infection.
Repeat paired testing should be performed if borderline values are reported.
The CDC states that the best clinical marker for Lyme disease is the initial skin lesion erythema migrans (EM), which occurs in 60% to 80% of patients.
CDC laboratory criteria for the diagnosis of Lyme disease include the following factors:
- Isolation of B. burgdorferi from a clinical specimen
- IgM and IgG antibodies in blood or CSF
- Paired acute and convalescent blood samples showing significant antibody response to B. burgdorferi

Interfering Factors

False-positive results may occur with high levels of rheumatoid factors or in the presence of other spirochete infections, such as syphilis (cross-reactivity).
Asymptomatic individuals who spend time in endemic areas may have already produced antibodies to B. burgdorferi.

Interventions

Pretest Patient Care

Assess patient’s clinical history, exposure risk, and knowledge regarding the test. Explain test purpose and procedure as well as possible follow-up testing.
Follow guidelines in Chapter 1 regarding safe, effective, informed pretest care.

Posttest Patient Care

Interpret test outcomes for a positive test. Advise the patient that follow-up testing may be required to monitor response to antibiotic therapy.
Unlike other diseases, people do not develop resistance to Lyme disease after infection and may continue to be at high risk, especially if they live, work, or recreate in areas where Lyme disease is present.
If Lyme disease has been ruled out, further testing may include Babesia microti, a parasite transmitted to humans by a tick bite. Symptoms include loss of appetite, fever, sweats, muscle pain, nausea, vomiting, and headaches.
Follow guidelines in Chapter 1 regarding safe, effective, informed posttest care.

Legionnaires’ Disease Antibody Test

Legionnaires’ disease is a respiratory condition caused by Legionella pneumophila. It is best diagnosed by organism culture; however, the organism is difficult to grow.

Detection of L. pneumophila in respiratory specimens by means of direct fluorescent antibody (DFA) technique is useful for rapid diagnosis but lacks sensitivity when only small numbers of organisms are available. Serologic tests should be used only if specimens for culture are not available or if culture and DFA produce negative results.

Reference Values

Normal

Negative for legionnaires’ disease by indirect fluorescent antibody (IFA) test or ELISA

Clinical Implications

A dramatic rise of titer levels to more than 1:128 in the interval between acute- and convalescent-phase specimens occurs with recent infections.
Serologic tests, to be useful, must be performed on an acute (within 1 week of onset) and convalescent (3 to 6 weeks later) specimen.
Serologic testing is valuable because it provides a confirmatory diagnosis of L. pneumophila infection when other tests have failed. IFA is the serologic test of choice because it can detect all classes of antibodies.
Demonstration of L. pneumophila antigen in urine by ELISA is indicative of infection.

Chlamydia Antibody IgG Test

Chlamydia is caused by a genus of bacteria (Chlamydia spp.) that require living cells for growth and are classified as obligate cell parasites. Recognized species include Chlamydia psittaci, Chlamydia pneumoniae, and Chlamydia trachomatis. C. psittaci causes psittacosis in birds and humans. C. pneumoniae is responsible for approximately 10% of cases of community-acquired pneumonia. C. trachomatis is grouped into three serotypes. One group causes lymphogranuloma venereum (LGV), a venereal disease. Another group causes trachoma, an eye disease. The third group causes genital tract infections different from LGV. Culture of the organism is definitive for chlamydiae. C. trachomatis infection is the most common reportable sexually transmitted infection (STI) in the United States. The national infection rate for C. trachomatis is estimated to be 3 million cases annually.

Because Chlamydia organisms are difficult to culture and grow, antibody testing aids in diagnosis of chlamydial infection.

Reference Values

Normal

Negative for chlamydia antibody by complement fixation (CF), IFA, and polymerase chain reaction (PCR) tests

Clinical Implications

Presence of antibody titer indicates past chlamydial infection. A fourfold or greater rise in antibody titer between acute and convalescent specimens indicates recent infection. Serologic tests cannot differentiate among the species of Chlamydia.
Infection with psittacosis is revealed in an elevated antibody titer. History will reveal contact with infected birds (pets or poultry).
LGV in males is characterized by swollen and tender inguinal lymph nodes. In females, swelling occurs in the intra-abdominal, perirectal, and pelvic lymph nodes. Chlamydia causes urethritis in males. It can infect the female urethra and endocervix, and it is also a cause of pelvic inflammatory disease in females. Eye disease caused by Chlamydia is endemic in parts of Africa, the Middle East, and Southeast Asia, although its presence is established worldwide. Culture and stained smear identification of the organism is diagnostic.

Interfering Factors

Depending on geographic location, nonspecific titers can be found in the general healthy population.

Streptococcal Antibody Tests: Antistreptolysin O Titer (ASO), Streptozyme, Antideoxyribonuclease-B Titer (Anti-DNase-B, ADNase-B) (ADB, Streptodornase)

Group A β-hemolytic streptococci are associated with streptococcal infections or illness.

These tests detect antibodies to enzymes produced by organisms. Group A β-hemolytic streptococci produce several enzymes, including streptolysin O, hyaluronidase, and DNase B. Serologic tests that detect these enzyme antibodies include antistreptolysin O titer (ASO), which detects streptolysin O; streptozyme, which detects antibodies to multiple enzymes; and anti-DNase B (ADB), which detects DNase B. Serologic detection of streptococcal antibodies helps to establish prior infection but is of no value for diagnosing acute streptococcal infections. Acute infections should be diagnosed by direct streptococcal cultures or the presence of streptococcal antigens.

The ASO test aids in the diagnosis of several conditions associated with streptococcal infections, such as rheumatic fever, glomerulonephritis, endocarditis, and scarlet fever. Serial rising titers over several weeks are more significant than a single result. ADB antibodies may appear earlier than ASO in streptococcal pharyngitis, and this test is more sensitive for streptococcal pyoderma.

Reference Values

Normal

ASO titer:

Adult: <160 Todd units/mL or <200 IU

Child (5 to 12 years of age): 170-330 Todd units/mL Anti-DNase B (ADB): A negative test is normal.

Preschool-aged children: <60 Todd units/mL

School-aged children: <170 Todd units/mL

Adults: <85 Todd units/mL

Streptozyme: negative for streptococcal antibodies

Clinical Implications

In general, a titer >160 Todd units/mL is considered a definite elevation for the ASO test.
The ASO or the ADB test alone is positive in 80% to 85% of group A streptococcal infections (e.g., streptococcal pharyngitis, rheumatic fever, pyoderma, glomerulonephritis).
When ASO and ADB tests are run concurrently, 95% of streptococcal infections can be detected.
A repeatedly low titer is good evidence for the absence of active rheumatic fever. Conversely, a high titer does not necessarily mean rheumatic fever of glomerulonephritis is present; however, it does indicate the presence of a streptococcal infection.
ASO production is especially high in rheumatic fever and glomerulonephritis. These conditions show marked ASO titer increases during the symptomless period preceding an attack. Also, ADB titers are particularly high in pyoderma.

Interfering Factors

An increased titer can occur in healthy carriers.
Antibiotic therapy suppresses streptococcal antibody response.
Increased B-lipoprotein levels inhibit streptolysin O and produce falsely high ASO titers.

Helicobacter pylori (HPY) IgG Antibody Serum, Stool, and Breath (PY) Test

H. pylori (previously known as Campylobacter pylori) is a bacterium associated with gastritis, duodenal and gastric ulcers, and possibly gastric carcinoma. The clinician orders this test when screening a patient for possible H. pylori infection. The organism is present in 95% to 98% of patients with duodenal ulcers and 60% to 90% of patients with gastric ulcers. A person with gastrointestinal symptoms with evidence of H. pylori colonization (e.g., presence of specific antibodies, positive breath test, positive culture, positive biopsy) is considered to be infected with H. pylori. A person without gastrointestinal symptoms having evidence of the presence of H. pylori is said to be colonized rather than infected.

This test detects H. pylori infection of the stomach. Traditionally, the presence of H. pylori has been detected through biopsy specimens obtained by endoscopy. As with any invasive procedure, there is risk and discomfort to the patient. Noninvasive methods of detection include the following:

Breath: measures isotopically labeled CO₂ in breath specimens
Stool: H. pylori stool antigen test (HpSa)

The presence of H. pylori-specific IgG antibodies has been shown to be an accurate indicator of H. pylori colonization. ELISA testing relies on the presence of H. pylori IgG-specific antibody to bind to antigen on the solid phase, forming an antigen-antibody complex that undergoes further reactions to produce a color indicative of the presence of antibody and is quantified using a spectrophotometer or ELISA microweld plate reader. The sensitivity is 94% and specificity 78%, compared with an invasive procedure, such as biopsy, for which the sensitivity is 93% and specificity 99%.

Reference Values

Normal

Negative for H. pylori by ELISA indicates no detectable IgG antibody in serum or stool. A positive result indicates the presence of detectable IgG antibody in serum or stool.

Breath

Negative: <50 disintegrations per minute (DPM) for H. pylori 50-199 DPM indeterminate for H. pylori >200 DPM positive for H. pylori

Procedure

1. Collect a 7-mL blood serum sample in a red-topped tube. Observe standard precautions. Place specimen in a biohazard bag for transport to the laboratory.
Be aware that a random stool specimen may be ordered to test for the presence of H. pylori antigen.
Remember that the breath test is a complex procedure and requires a special kit. Ensure that the collection balloon is fully inflated. Transfer the breath specimen to the laboratory. Keep at room temperature.
The¹³C-urea breath test (¹³C-UBT) requires the patient to swallow an isotopically labeled (¹³C) urea tablet. The urea is subsequently hydrolyzed to ammonia and labeled CO₂ by the presence of H. pylori urease activity. After approximately 30 minutes, an exhaled breath sample is collected, and¹³CO₂ levels are assessed using isotope ratio mass spectrometry.

Interventions

Pretest Patient Care

Explain test purpose, procedure, and knowledge of signs and symptoms and risk factors for transmission: close living quarters, many persons in household, poor household sanitation and hygiene. The patient swallows a capsule before a breath specimen is obtained. The serum antibody test would be appropriate for a previously untreated patient with a documented history of gastroduodenal ulcer disease and unknown H. pylori infection status.
Follow guidelines in Chapter 1 regarding safe, effective, informed pretest care.

Posttest Patient Care

Interpret test outcomes in light of patient’s history, including other clinical and laboratory findings. Explain treatment (4 to 6 weeks of antibiotics to eradicate H. pylori and medication to suppress acid production) and need for follow-up testing. Transmission is unknown, but the potential for transmission may occur during episodes of gastrointestinal illness, particularly with vomiting. Many persons may be infected with H. pylori but are asymptomatic.
Follow guidelines in Chapter 1 regarding safe, effective, informed posttest care.

VIRAL TESTS

Epstein-Barr Virus (EBV) Antibody Tests: Infectious Mononucleosis (IM) Slide (Screening) Test, Heterophile Antibody Titer, Epstein-Barr Antibodies to Viral Capsid Antigen and Nuclear Antigen

Epstein-Barr virus (EBV) is a herpesvirus found throughout the world. The most common symptomatic manifestation of EBV infection is a disease known as infectious mononucleosis (IM). This disease induces formation of increased numbers of abnormal lymphocytes in the lymph nodes and stimulates increased heterophile antibody formation. IM occurs most often in young adults who have not been previously infected through contact with infectious oropharyngeal secretions. Symptoms include fever, pharyngitis, and lymphadenopathy. EBV is also thought to play a role in the etiology of Burkitt’s lymphoma, nasopharyngeal carcinoma, and chronic fatigue syndrome.

The most common test for EBV is the rapid slide test (Monospot) for heterophile antibody agglutination. The heterophile antibody agglutination test is not specific for EBV and therefore is not useful for evaluating chronic disease. If the heterophile test is negative in the presence of acute IM symptoms, specific EBV antibodies should be determined. These include antibodies to viral capsid antigen (anti-VCA) and antibodies to EBV nuclear antigen (EBNA) using IFA and ELISA tests.

Diagnosis of IM is based on the following criteria: clinical features compatible with IM, hematologic picture of relative and absolute lymphocytosis, and presence of heterophile antibodies.

Reference Values

Normal

Negative for IM by latex agglutination

Negative for EBV antibodies by IFA or ELISA

Interventions

Pretest Patient Care

Assess patient’s clinical history, symptoms, and test knowledge. Explain test purpose and procedure. If preliminary tests are negative, follow-up tests may be necessary.
Follow guidelines in Chapter 1 regarding safe, effective, informed pretest care.

Posttest Patient Care

Interpret test outcomes; see Interpreting Results of Immunologic Tests. Explain treatment (e.g., supportive therapy [intravenous fluids]). After primary exposure, a person is considered immune. Recurrence of IM is rare.
Remember that resolution of IM usually follows a predictable course: pharyngitis disappears within 14 days after onset; fever subsides within 21 days; and fatigue, lymphadenopathy, and liver and spleen enlargement regress by 21 to 28 days.
Follow guidelines in Chapter 1 regarding safe, effective, informed posttest care.

Hepatitis Tests: Hepatitis A (HAV), Hepatitis B (HBV), Hepatitis C (HCV), Hepatitis D (HDV), Hepatitis E (HEV), Hepatitis G (HGV)

Hepatitis can be caused by viruses and several other agents, including drugs and toxins. Approximately 95% of hepatitis cases are due to five major virus types: hepatitis A, B, C, D, and E (Table 8.4). Diagnosing the specific virus is difficult because the symptoms (e.g., chills, weight loss, fever, distaste for cigarettes and food, darker urine and lighter stool) presented by each viral type are similar. Additionally, some individuals may be asymptomatic or have very mild symptoms that are ascribed to the “flu.” Serologic tests for hepatitis virus markers have made it easier to define the specific type.

Hepatitis A virus (HAV), which is acquired through enteric transmission, infects the gastrointestinal tract and is eliminated through the feces. Serologically, the presence of the IgM antibody to HAV (IgM anti-HAV) and the total antibody to HAV (total anti-HAV) identifies the disease and determines previous exposure to or recovery from HAV.

Hepatitis B virus (HBV) demonstrates a central core containing the core antigen and a surrounding envelope containing the surface antigen: less than 0.01 pg/mL for viral load. Detection of core antigen (HBcAg), envelope antigen (HBeAg), and surface antigen (HBsAg) or their corresponding antibodies constitutes hepatitis B serologic or plasma assessment. Viral transmission occurs through exposure to contaminated blood or blood products through an open wound (e.g., needle sticks, lacerations). Hepatitis monitoring panel for serial testing includes four B markers: HBsAg, HBeAg, anti-HBe, and anti-HBs. Interpretation depends on clinical setting. Hepatitis B DNA Ultra Sensitive Quantitative PCR is the most sensitive test available for hepatitis B viral load.

Hepatitis C virus (HCV), formerly known as non-A, non-B hepatitis, is also transmitted parenterally. HCV infection is characterized by presence of antibodies to hepatitis C (anti-HCV) and levels of
alanine aminotransferase (ALT) that fluctuate between normal and markedly elevated. Levels of anti-HCV remain positive for many years; therefore, a reactive test indicates infection with HCV or a carrier state but not infectivity or immunity. PCR or reverse transcriptase PCR (RT-PCR) (viral load), which detects HCV RNA, should be used to confirm infection when acute hepatitis C is suspected. A negative hepatitis C antibody (recombinant immunoblot assay [RIBA]) does not exclude the possibility of HCV infection because seroconversion may not occur for up to 6 months after exposure.

TABLE 8.4 Hepatitis Test Findings in Various Stages

Disease Stages	Viral Specific and Serologic Tests
Disease Stages	HAV	HBV	HCV	HDV	HEV
Acute	IgM anti-HAV	IgM anti-HBc, HBsAg	Anti-HCV	HDAg	IgM anti-HEV
Chronic	Fecal HAV 1-2 wk before symptoms	2%-10% of all persons >5 yr will progress to chronic infection	85% Anti-HCV	6% total anti-HDV	None
Infectivity	None	HBeAg, HBsAg, HBV-DNA	Anti-HCV	Total anti-HDV	None
Recovery	None	Anti-HBe, anti-HBs	None	None	None
Viral load (viral genome)		HBV DNA	HCV RNA
Carrier state	None	HBsAg	None	HBAg, anti-HDV	None
Immunity	Total anti-HAV	Anti-HBs, total anti-HBc	None	None	Uncertain
Acute viral panel	IgM anti-HAV	HBsAg	Anti-HCV, HIV test also

Hepatitis D virus (HDV) is encapsulated by the HBsAg. Without the HBsAg coating, HDV cannot survive. Because HDV can cause infection only in the presence of active HBV infection, it is usually found where a high incidence of HBV occurs. Transmission is parenteral. Serologic HDV determination is made by detection of the hepatitis D antigen (HDAg) early in the course of the infection and by detection of anti-HDV antibody (anti-HDV) in the later stages of the disease.

Hepatitis E virus (HEV) is transmitted enterically and is associated with poor hygienic practices and unsafe water supplies, especially in developing countries. It is quite rare in the United States. Specific serologic tests include detection of IgM and IgG antibodies to hepatitis E (anti-HEV).

Hepatitis G virus (HGV) is transmitted by contaminated blood supply and is seen when HCV and HBV are detected together. See Table 8.5 for a summary of the features of the different hepatitis agents.

The following terms are used:

ALT (alanine aminotransferase): an enzyme normally produced by the liver; blood levels may

increase in cases of liver damage Anti-HBc: antibody to hepatitis B core antigen Anti-HBe: antibody to hepatitis B envelope antigen Anti-HBs: antibody to hepatitis B surface antigen

TABLE 8.5 Summary of Clinical and Epidemiologic Features of Viral Hepatitis Agents

Features		Hepatitis A	Hepatitis B	Hepatitis C	Hepatitis D	Hepatitis E	Hepatitis G Scan With HBV + HCV
Incubation period		45-50 d	30-150 d	15-110 d	30-150 d	230-240 d	Questionable
Onset		Abrupt	Insidious	Insidious	Abrupt	Insidious	Unknown
Jaundice		Children: 10%; adults: 70%-80%	25%	25%	Varies	Unknown	No
Asymptomatic patients		Most children	Most children; adults: 50%	About 75%	Rare	Rare	Contaminated blood
Routes of transmission
	Fecal/oral	Yes	No	No	No	Yes	No
	Parenteral	Rare	Yes	Yes	Yes	No	Blood supply
	Sexual	No	Yes	Possible	Yes	No	No
	Perinatal	No	Yes	Possible	Possible	No	No
	Water/food	Yes	No	No	No	Yes	Yes
Chronic state		No	Adults: 6%-10%; children: 25%-50%; infants: 70%-90%	50%	10%—15%	No	Yes
Case fatality rate		0.6%	1.4% Liver cancer	1%-2% Liver cancer with HBV and HCV	30%	1%-2% Pregnant women: 20%	Unknown

Antibody: a Y-shaped protein molecule (immunoglobulin) in serum or body fluid that either neutralizes an antigen or tags it for attack by other cells or chemicals; acts by uniting with and firmly binding to an antigen. The prefix anti- followed by initials of a virus refers to specific antibody against the virus.

Chronic hepatitis: a condition in which symptoms or signs of hepatitis persist for >6 months

Cirrhosis: irreversible scarring of the liver that may occur after acute or chronic hepatitis

Delta agent: a unique RNA virus that causes acute or chronic hepatitis; requires HBV for replication and infects only patients who are HBsAg-positive; is composed of a delta antigen core and an

HBsAg coat; also known as HDV Endemic: present in a community at all times but occurring in a small number of cases

Enteric route: spread of organisms through the oral-intestinal-fecal cycle

Flavivirus: a family of small RNA viruses; HCV is similar to members of the Flavivirus family

Fulminant hepatitis: the most severe form of hepatitis; may lead to acute liver failure and death

HBcAg: hepatitis B core antigen

HBsAg: hepatitis B surface antigen

Hepatotropic: having an affinity for or exerting a specific effect on the liver

IgG: a form of immunoglobulin that occurs late in an infectious process

IgM: a form of immunoglobulin that occurs early in an infectious process

IgM anti-HAV: M-class immunoglobulin antibody to HAV

IgM anti-HBc: M-class immunoglobulin antibody to HBcAg

Immune globulin: a sterile solution of water-soluble proteins that contains those antibodies normally present in adult human blood; used as a passive immunizing agent against various viruses such as HAV

Negative-sense RNA virus: a virus in which the viral proteins are encoded by messenger RNA molecules that are complementary to the viral genome

New viruses—GBV-A, GBV-B, and GBV-C: may be causative agents in non-A through E hepatitis

Non-A, non-B hepatitis: viral hepatitis caused by viruses other than A, B, or D (e.g., C, E)

Parenteral: entering the body subcutaneously, intramuscularly, or intravenously or other means whereby the organisms reach the bloodstream directly

Positive-sense RNA virus: a virus in which the parenteral (or genomic) RNA serves as the messenger RNA for protein synthesis

Recombinant antigen: an antigen that results from the recombination of genetic components, which then are artificially introduced into a cell, leading to synthesis of a new protein

Viral load: the amount or concentration of virus in the circulation

These measurements are used for differential diagnosis of viral hepatitis, viral load. Serodiagnosis of previous exposure and recovery of viral hepatitis is complex because of the number of serum or plasma markers necessary to determine the stage of illness. Testing methods include ELISA, microparticle enzyme immunoassay (MEIA), PCR, and RT-PCR and tests for viral genome (viral load).

Indications for Hepatitis A Vaccine

Pre-exposure Protection

Children should be vaccinated between 12 and 23 months of age.
Communities with existing vaccination programs for children 2 to 18 years of age should maintain their programs.
In areas without vaccination programs, catch-up vaccination of unvaccinated children 2 to 18 years of age can be considered.

Individuals at Increased Risk

Persons traveling to or working in countries that have high or intermediate endemicity
Users of injection and noninjection illicit drugs
Persons with clotting-factor disorders who have received solvent-detergent, treated high-purity factor VIII concentrates
Homosexual men
Individuals working with nonhuman HAV-infected primates
Food handlers
Persons employed in child care centers
Health care workers
Susceptible individuals with chronic liver disease

Indications for Hepatitis B Vaccine

Family members of adoptees from foreign countries who are HBsAg positive
Health care workers (dentist, DO, MD, RN, and trainees in health care fields)
Hemodialysis patients or patients with early renal failure
Household or sexual contacts of persons chronically infected with hepatitis B
Immigrants from Africa or Southeast Asia; recommended for children <11 years old and all susceptible household contacts of persons chronically infected with hepatitis B
Injection drug users
Inmates of long-term correctional facilities
Clients and staff of institutions for the developmentally disabled
International travelers to countries of high or intermediate HBV endemicity
Laboratory workers
Public safety workers (e.g., police, fire fighters)
Recipients of clotting factors. Use a fine needle (<23 gauge) and firm pressure at injection site for >2 minutes.
Persons with STIs or multiple sexual partners in previous 6 months, prostitutes, homosexual and bisexual men
Postvaccination blood testing is recommended for sexual contacts of HBsAg-positive persons; health care workers, recipients of clotting factors, those who are HBsAg-positive are at high risk.
Persons in nonresidential day care programs should be vaccinated if an HBsAg-positive classmate behaves aggressively or has special medical problems that increase the risk for exposure to blood. Staff in nonresidential day care programs should be vaccinated if a client is HBsAg-positive.
- Observe enteric and standard precautions for 7 days after onset of symptoms or jaundice with hepatitis B. Hepatitis A is most contagious before symptoms or jaundice appears.
- Use standard blood and body fluid precautions for type B hepatitis and B antigen carriers. Precautions apply until the patient is HBsAg negative and the anti-HBs appears. Avoid “sharps” (e.g., needles, scalpel blades) injuries. Should accidental injury occur, encourage some bleeding, and wash area well with a germicidal soap. Report injury to proper department, and follow up with necessary interventions. Put on gown when blood splattering is anticipated. A private hospital room and bathroom may be indicated.
Persons with a history of receiving blood transfusion should not donate blood for 6 months. Transfusion-acquired hepatitis may not show up for 6 months after transfusion. Persons who test positive for HBsAg should never donate blood or plasma.
Persons who have sexual contact with hepatitis B-infected individuals run a greater risk for acquiring that same infection. HBsAg appears in most body fluids, including saliva, semen, and cervical secretions.
Observe standard precautions in all cases of suspected hepatitis until the diagnosis and hepatitis type are confirmed.

Reference Values

Normal

Negative (nonreactive) for hepatitis A, B, C, D, or E by ELISA, MEIA, PCR, RIBA, or RT-PCR
Negative or undetected viral load (not used for primary infection, only to monitor). PCR requires a separate specimen collection.
Hepatitis B viral DNA (HBV-DNA) negative or nonreactive viral load (<0.01 pg/mL) in an infected individual before treatment

Procedure

Collect a 7-mL blood serum sample in a red-topped tube or two lavender-topped ethylenediaminetetraacetic acid (EDTA) tubes, 5 mL each, for plasma. Observe standard precautions. Centrifuge promptly and aseptically. Place specimen in a biohazard bag for transport to the laboratory. Send specimens frozen on dry ice. Check with your laboratory for protocols and whether plasma or serum is needed.
Some specimens need to be split into two plastic vials before freezing and sent frozen on dry ice. Check with your laboratory.

Clinical Implications

Individuals with hepatitis may have generalized symptoms resembling the flu and may dismiss their illness as such.
A specific type of hepatitis cannot be differentiated by clinical observations alone. Testing is the only sure method to define the category (see Tables 8.6 and 8.7).
Rapid diagnosis of acute hepatitis is essential for the patient so that treatment can be instituted and for those who have close patient contact so that protective measures can be taken to prevent disease spread.
Persons at higher risk for acquiring hepatitis A include patients and staff in health care and custodial institutions, people in day care centers, intravenous drug abusers, and those who travel to undeveloped countries or regions where food and water supplies may be contaminated.
Persons at higher risk for hepatitis B include those with a history of drug abuse, those who have sexual contact with infected persons, those who have household contact with infected persons, and especially those with skin and mucosal surface lesions (e.g., impetigo, saliva from chronic HBV-infected persons on toothbrush racks and coffee cups in their homes); additionally, infants born to infected mothers (during delivery), hemodialysis patients, and health care employees are at higher risk for infection. Of all persons with HBV infection, 38% to 40% contract HBV during early childhood.
Health care workers should be periodically tested for hepatitis exposure and should always observe standard precautions when caring for patients.
Persons at risk for hepatitis C include those who have received blood transfusions, engage in intravenous drug abuse, undergo hemodialysis, have had organ transplantation, or have sexual contact with an infected person; hepatitis C can also be transmitted during delivery from mother to neonate. Most people are asymptomatic at the time of diagnosis for hepatitis C. See Table 8.8 for hepatitis markers that appear after infection.
Both total (IgG + IgM) and IgM anti-HBc are positive in acute infection, whereas typically only total anti-HBc is present in chronic infection.

Interventions

Pretest Patient Care

Assess patient’s social and clinical history and knowledge of test. Explain test purpose and procedure.
Follow guidelines in Chapter 1 regarding safe, effective, informed pretest care.

Posttest Patient Care

Explain significance of test results and counsel appropriately regarding presence of infection, recovery, and immunity.
Counsel health care workers and family regarding protective and preventive measures necessary to avoid transmission.
Instruct patients to alert health care workers and others regarding their hepatitis history in situations in which exposure to body fluids and wastes may occur.
Pregnant women may need special counseling.
Follow guidelines in Chapter 1 regarding safe, effective, informed posttest care.

TABLE 8.6 Differential Diagnosis of Viral Hepatitis

Virus	Transmission	Incubation Period	Test for Acute Infection	Social and Clinical History
Hepatitis A	Fecal-oral by person-toperson contact or ingestion of contaminated food	Average, 30 d (range, 15-50 d)	IgM antibody to hepatitis A capsid proteins	Household or sexual contact with an infected person, day care centers, and common source outbreaks from contaminated food
Hepatitis B	Sexual, blood, and other body fluids	Average, 120 d (range, 45-160 d)	HBsAg; the best test for acute or recent infection is IgM antibody to HBcAg	Sexual promiscuity, male-to-maleto-female sexual practices, injection drug use, birth to an infected mother
Hepatitis C	Blood	Commonly 6-9 wk (range, 2 wk-6 mo)	ELISA is the initial test to show if ever infected; it should be confirmed by another test such as PCR	Injection drug use, occupational exposure to blood, hemodialysis, transfusion, possibly sexual transmission
Hepatitis D	Sexual, blood, and other body fluids	2-8 wk (from animal studies)	Total antibody to delta hepatitis shows if ever infected; IgM test is in research laboratories; ELISA	Requires active infection with HBV; injection drug users and persons receiving clotting factor concentrates are at highest risk for infection
Hepatitis E	Fecal-oral	Average, 26-42 d (range, 15-64 d)	Research laboratories	No known cases originated in the United States; international travelers are the only high-risk group to date
Hepatitis G	Blood	Unknown	Occurs with hepatitis B and hepatitis C	Recipient of contaminated blood

TABLE 8.7 Viruses for Which Clinical Signs and Symptoms Mimic Hepatitis

Virus	Transmission	Incubation Period	Test for Acute Infection	Social and Clinical History
Epstein-Barr virus (EBV)	Oropharyngeal (saliva)	4-6 wk	IgM antibody to EBV viral capsid	Seroconversion by age 5 yr in 50% of persons in the United States; children with an acutely infected sibling are at greater risk
Cytomegalovirus (CMV, human herpes-virus 5)	Intimate contact with infected fluids; sexual, perinatal, blood transfusion, and infected breast milk	About 3-8 wk for transfusionacquired CMV	Culture, monoclonal antibody to early antigen	Household sexual contact with an infected person, male-to-male sexual practices, day care centers, perinatal transmission

TABLE 8.8 Markers That Appear After Infection

Serologic Marker	Time Marker Appears After Infection	Clinical Implications
Hepatitis A Virus HAV-Ab/IgM	4-6 wk	Positive for acute stage of hepatitis A, develops early in disease course
HAV-Ab/IgG	8-12 wk	Indicates previous exposure and immunity to hepatitis A
Hepatitis B Virus
HBsAg-hepatitis B virus	12 wk	Positive in acute stage of hepatitis B; earliest indicator of acute antigen infection; also indicates chronic infection
HBeAg	4-12 wk	Positive in acute active stage with viral replication (infectivity factor); highly infective
HBcAb	6-14 wk	This marker may remain in serum for a longer time; together with HBsAB represents convalescent stage; indicates past infection
HBcAb IgM	6-14 wk	Indicates acute infection
HBeAb antibody	8-16 wk	Indicates acute infection resolution
HBsAb antibody	4-10 mo	Indicates previous exposure, clinical recovery, immunity to hepatitis B, not necessarily to other types of hepatitis; marker for permanent immunity to hepatitis B

CLINICAL ALERT

Observe enteric and standard precautions for 7 days after onset of symptoms or jaundice in hepatitis A. Hepatitis A is most contagious before symptoms or jaundice appears.
Use standard blood and body fluid precautions with hepatitis B and hepatitis B antigen carriers. Precautions apply until the patient is HBsAg negative and anti-HBs appears. Avoid “sharps” (e.g., needles, scalpel blades) injuries. Should accidental injury occur, encourage some bleeding, and wash area well with a germicidal soap. Report injury to proper department and follow up with necessary interventions. Put on gown when blood splattering is anticipated. A private hospital room and bathroom may be indicated.
If patient has had a blood transfusion, he or she should not donate blood for 6 months. Transfusion-acquired hepatitis may not show up for 6 months after transfusion. Persons who test positive for HBsAg should never donate blood or plasma.
Persons who have sexual contact with hepatitis B-infected individuals run a greater risk for acquiring the infection. HBsAg appears in most body fluids, including saliva, semen, and cervical secretions.
Standard precautions must be observed in all cases of suspected hepatitis until the diagnosis and hepatitis type are confirmed.
Immunization of persons exposed to the infection should be done as soon as possible. In the case of contact with hepatitis B, both hepatitis B immunoglobulin (HBIG) and HBV vaccine should be administered within 24 hours of skin-break contact and within 14 days of last sexual contact. For hepatitis A, immune globulin (IG) should be given within 2 weeks of exposure. In day care centers, IG should be given to all contacts (children and personnel).

Human Immunodeficiency Virus (HIV-1/2) Antibody Tests, HIV Group O, Antibody to Human Immunodeficiency Virus (HIV-1/2); Acquired Immunodeficiency Syndrome (AIDS) Tests

These tests detect human immunodeficiency viruses types 1 and 2 (HIV-1/2), which cause AIDS. Infection with HIV-1 is most prevalent in the United States and Western Europe. Most cases associated with HIV-2 are reported in West Africa. Tests to detect the presence of HIV-1 antibody screen blood and blood products that will be used for transfusion and tissue and organs for transplantation. They are also used to test people at risk for developing AIDS, such as intravenous drug users, sexual partners of HIV-infected persons, and infants born to HIV-infected women (Table 8.9). The diagnosis of AIDS must be clinically established. Tests used to determine the presence of antibodies to HIV-1 include ELISA, Western blot, and PCR. PCR has been evaluated as a means to detect viral load by viral nucleic acid test (NAT) after infection but before seroconversion.

A single reactive ELISA test by itself cannot be used to diagnose AIDS. The test should always be repeated in duplicate using the same blood sample. If repeatedly reactive, follow-up tests using Western blot should be done. A positive Western blot is considered confirmatory for HIV. The combination HIV-1/2 test has replaced the HIV-1 test for screening blood and blood products for transfusion. It is also used for testing potential organ transplant donors.

TABLE 8.9 Diagnostic Testing for HIV

Whom to Test	How to Test	When to Test
Men who have sex with men, IV drug users, recreational drug users, those engaging in unprotected sex, those attending STD clinics, pregnant women, those with signs and symptoms of unusual pneumonia, skin lesions, mononucleosis-like syndrome; persons known to be infected with HIV	Screening EIA and confirmatory tests. Western blot confirmatory test detects antibodies to HIV-1 core antigens: gp41, gp120, gp160, p18, p24, p31, p40, p65, p55/51. IFA confirmatory test detects potent antibodies by fluorescein-tagged secondary antibodies. Viral RNA and p24 antigen are used along with CD4 count to monitor treatment. Nucleic acid amplification testing (NAT) to monitor “viral load.” Rapid testing: single-use diagnostic system (SUDS) results in 1 hour.	As early a detection as possible so that proper treatment, decrease in transmission, and modified behaviors can occur. Mother-to-child (vertical transmission) treated during pregnancy and delivery, and exposed infants within 48 hours of delivery; transmission of HIV can occur in utero, during birth, and by breast-feeding.

Reference Values

Normal

Negative for HIV antibodies against HIV antigens types 1 and 2 by ELISA, enzyme immunoassay (EIA), and Western blot HIV proviral RNA: not reactive or negative by PCR HIV proviral DNA: not reactive or negative HIV core P24 antigen: not reactive or negative NAT: Viral load is low.

Procedure

Serum Testing

Collect a 7-mL blood serum sample in a red-topped tube. Plasma may also be used. Observe standard precautions. Place specimen in biohazard bag for transport to the laboratory.

NOTE

The U.S. Food and Drug Administration (FDA) has approved a rapid point-of-care whole blood test. The OraQuick Rapid HIV-1 Antibody Test (OraSure Technologies, Inc., Bethlehem, PA) uses whole blood obtained from a finger stick. Results are available within 60 minutes; however, a positive test should be subsequently confirmed by an acceptable test, such as Western blot or IFA. Other FDA-approved rapid HIV screening tests include Uni-Gold Recombigen HIV (Trinity Biotech USA, Jamestown, NY), Reveal G3 Rapid HIV-1 Antibody Test (MedMira Laboratories, Inc., Nova Scotia, Canada), and Clearview COMPLETE HIV 1/2 (Chembio Diagnostic System, Inc., Medford, NY).

Oral Testing

Saliva specimens may also be collected and are usually indicated in clinic settings or outreach environments—that is, point-of-care settings. The oral fluid HIV diagnostic kit can provide results in as little as 20 minutes; however, a positive test should be confirmed with more specific testing, such as Western blot or IFA. See Chart 8.1 for additional applications for oral testing.
Use a special testing kit such as the commercial OraSure HIV-1 Oral Specimen Collection Device (OraSure Technologies, Inc., Bethlehem, PA). The kit includes a specially treated cotton pad on a nylon stick and a vial containing preservative solution. Salt solution in the pad facilitates absorption of the required fluid.
Place the cotton pad between the lower cheek and gum, rub back and forth until moistened, and leave in place for 2 minutes. Remove specially treated pad and place it in the vial of special antimicrobial preservative solution. Place specimen container in a biohazard bag and transport to laboratory.
The Omni-SAL (Saliva Diagnostic Systems, Brooklyn, NY) device employs a different collection method in which a cotton pad is placed under the tongue. An indicator in the collecting device changes color when an adequate amount of oral fluid has been collected.

Clinical Implications

A positive test is associated with viral replication and appearance of HIV antibodies (IgM, IgG).
A positive ELISA that fails to be confirmed by Western blot or IFA should not be considered negative, especially in the presence of symptoms or signs of AIDS. Repeat testing in 3 to 6 months is suggested.
A positive result may occur in noninfected persons because of unknown factors.
Negative tests tend to rule out AIDS in high-risk patients who do not have the characteristic opportunistic infections or tumors.
An HIV infection is described as a continuum of stages that range from the acute, transient, mononucleosis-like syndrome associated with seroconversion to asymptomatic HIV infection to symptomatic HIV infection and, finally, to AIDS. AIDS is end-stage HIV infection.
Treatments are more effective and less toxic when begun early in the course of HIV infection.
HIV PCR method to determine viral load may be performed during HIV treatment to monitor patient prognosis and treatment.
Diagnosis of HIV in neonates is difficult because maternally acquired antibodies may be present until the child is 18 months of age. Additionally, PCR to detect antigen is usually not successful until the child is 6 months of age.

Interfering Factors

Nonreactive HIV test results occur during the acute stage of disease when the virus is present but antibodies are not sufficiently developed to be detected. It may take up to 6 months for the test
result to become positive. During this stage, the test for the HIV antigen may confirm an HIV infection (Fig. 8.1).
Test kits for HIV are extremely sensitive. As a result, nonspecific reactions may occur if the tested person has been previously exposed to HIV human cells or the growth media.

FIGURE 8.1. Time course for appearance of viral and serologic markers during primary HIV infection. (Modified from Busch MP, Satten GA. Time course of viremia and antibody seroconversion following human immunodeficiency virus exposure. Am J Med 1997;102(5B):117—124. Reproduced with permission of EXCERPTA MEDICA, INC. via Copyright Clearance Center.)

Interventions

Pretest Patient Care

An informed, witnessed consent form must be properly signed by any person being tested for HIV/AIDS. This consent form must accompany the patient and the specimen (see Appendix F for sample form).
It is essential that counseling precedes and follows the HIV antibody test. This test should not be performed without the subject’s informed consent, and persons who need to access results legitimately must be mentioned. Discussion of the clinical and behavioral implications derived from the test results should address the accuracy of the test and should encourage behavioral modifications (e.g., sexual contact, shared needles, blood transfusions).
Assess frequency and intensity of symptoms: elevated temperature, anxiety, fear, diarrhea, neuropathy, nausea and vomiting, depression, and fatigue.
Infection control measures mandate use of standard precautions (see Appendix A).
Follow guidelines in Chapter 1 regarding safe, effective, informed pretest care.

CLINICAL ALERT

Issues of confidentiality surround HIV testing. Access to test results should be given judiciously on a need-to-know basis unless the patient specifically expresses otherwise. Interventions to block general computer access to this information are necessary; each health care facility must determine how best to accomplish this.
Conversely, health care workers directly involved with the care of an HIV/AIDS patient have a right to know the diagnosis so that they may protect themselves from exposure.
All results, both positive and negative, must be somehow entered in the patient’s health care records while maintaining confidentiality. People are more likely to test voluntarily when they trust that inappropriate disclosure of HIV testing information will not occur. Long-term implications include potential loss of jobs, housing, insurance coverage, and personal relationships.
The clinician must sign a legal form stating that the patient has been informed regarding test risks.
A person who exhibits HIV antibodies is presumed to be HIV infected; appropriate counseling, medical evaluation, and health care interventions should be discussed and instituted.
Positive test results must be reported to the state and federal public health authorities according to prescribed state regulations and protocols.
Anonymous testing and reporting is available, such as commercial home tests.

Posttest Patient Care

Interpret test outcomes. Explain significance of test results along with CD4⁺ cell counts. Advise patient that screening tests must be confirmed before the results are reported as HIV reactive. Provide options for immediate counseling if necessary. Explain treatment with potent antiviral drugs and protease inhibitors. The International AIDS Society-USA has recommended starting treatment with antiretroviral drugs if the CD4 cell count is <350/µL but before it reaches 200/µL. Plasma HIV-1 RNA level should be checked every 4 to 8 weeks until it is nondetectable and thereafter three to four times per year. Recently, the FDA has approved darunavir ethanolate for the treatment of HIV in antiretroviral treatment-experienced patients.
Follow guidelines in Chapter 1 regarding safe, effective, informed posttest care.

VIRAL ANTIBODY TESTS TO ASSESS IMMUNE STATUS

Rubella Antibody Tests

Rubella, a mild, contagious illness characterized by an erythematous maculopapular rash, is observed primarily in children 5 to 14 years of age and in young adults. The disease, commonly called German or 3-day measles, may be asymptomatic or may involve a 1- to 5-day prodromal period of malaise, headache, cold symptoms, low-grade fever, and suboccipital lymphadenopathy.

Although the illness is mild in children, it may cause the congenital rubella syndrome in the fetus of a mother infected early in pregnancy. As many as 85% of infants infected during the first 8 weeks of gestation have detectable defects by 4 years of age. The classic abnormalities associated with the rubella syndrome include congenital heart disease, cataracts, and neurosensory deafness. After 20 to 24 weeks of gestation, congenital abnormalities are rare.

The quantitative measurement of IgG antibodies to rubella virus aids in the determination of immune status. Assay results of 10 IU/mL of antibody are negative or not immune. Assay results >10 IU/mL are considered positive or immune. A positive result of IgM antibody indicates a congenital or recent infection. The measurement of IgM class antibodies for determination of acute-phase infection is recommended in all age groups. IgM rubella antibody determination is
usually not recommended when the patient is >6 months of age. Unlike IgG class antibodies, IgM antibodies are larger molecules and cannot cross the placenta, thus determining that the infant has an active form of the disease.

Reference Values

Normal

Negative for rubella IgG antibodies by ELISA or chemiluminescence (<7 IU/mL: no immunity)

Negative for IgM antibodies by ELISA or chemiluminescence (<0.9 IU/mL: no infection)

Positive for rubella IgG antibodies by ELISA or chemiluminescence (>10 IU/mL; immunity, indicates a current or previous exposure or immunization to rubella) Positive for rubella IgM antibodies (with or without positive IgG) by ELISA or chemiluminescence (>1.1 IU/mL; indicates a current or recent infection with rubella virus)

Clinical Implications

When testing for IgG antibody, seroconversion between acute and convalescent sera is considered strong evidence of a current or recent infection. The recommended interval between an acute and convalescent sample is 10 to 14 days.
A serum specimen taken very early during the acute stage of infection may contain levels of IgG antibody below 10 IU/mL.
Although the presence of IgM antibody suggests current or recent infection, low levels of IgM may occasionally persist for more than 12 months after infection or immunization. Passively acquired rubella antibody levels (IgG) in the infant (which can cross the placenta because of their smaller molecular size) decrease markedly within 2 to 3 months after infection.
IgM is detectable soon after clinical symptoms occur and reaches peak levels at 10 days.

Interventions

Pretest Patient Care

Assess patient’s test knowledge. Explain test purpose and procedure. Advise pregnant women that rubella infection acquired in the first trimester of pregnancy is associated with an increased incidence of miscarriage, stillbirth, and congenital abnormalities.
Follow guidelines in Chapter 1 regarding safe, effective, informed pretest care.

Posttest Patient Care

Interpret test outcome and counsel appropriately. Advise women of childbearing age who test negative to be immunized before becoming pregnant. Immunization is contraindicated during pregnancy. Patients who test positive are naturally immune to further rubella infections.
Follow guidelines in Chapter 1 regarding safe, effective, informed posttest care.

Measles (Rubeola) Antibody Tests

Classified as a paramyxovirus, measles produces a highly contagious respiratory infection. The disease is spread during the prodrome phase through direct contact with respiratory secretions in the form of droplets. Clinical infection with measles virus is characterized by high fever, cough, coryza, conjunctivitis, malaise, and Koplik’s spots on the buccal mucosa. An erythematous rash then develops behind the ears and over the forehead, spreading to the trunk.

Serology has become increasingly important as a tool for determining the immune status of the young adult population entering college or the military. In addition, the linkage between measles infection and premature delivery or spontaneous abortion supports screening pregnant mothers for susceptibility.

These tests determine susceptibility and immunity to measles virus. Since intensive immunization began in the United States in the 1970s, the incidence of measles infection has been reduced from approximately one half million cases annually (1960s) to fewer than 500 cases in recent years. Many individuals, however, may remain susceptible to measles virus because of vaccine failure or nonimmunization. A positive IgG coupled with a negative IgM result indicates previous exposure to measles virus and immunity to this viral infection. Positive IgM results, with or without positive IgG results, indicate a recent infection with measles virus.

Reference Values

Normal

Negative for measles IgG or IgM antibodies by ELISA: nonimmune

Positive for measles IgG antibody: immune; indicates a current or previous exposure or immunization to measles

Positive for measles IgM antibody (with or without positive IgG): indicates a recent infection with measles virus

Clinical Implications

When testing for IgG antibody, seroconversion between acute and convalescent sera is considered strong evidence of a current or recent infection. The recommended interval between an acute and convalescent sample is 10 to 14 days.
Although the presence of IgM antibody suggests current or recent infection, low levels of IgM may occasionally persist for more than 12 months after infection or immunization.
IgM antibody response is detectable 2 to 3 weeks after appearance of the rash.

Interventions

Pretest Patient Care

Assess patient’s test knowledge. Explain test purpose and procedure. Advise pregnant women that measles poses a high risk for serious complications and may be linked to premature delivery or spontaneous abortion.
Follow guidelines in Chapter 1 regarding safe, effective, informed pretest care.

Posttest Patient Care

Interpret test outcome and counsel appropriately. Advise women of childbearing age who test negative to be immunized before becoming pregnant. Inform patients who test positive that they are naturally immune to further measles infection.
Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Mumps Antibody Tests

The mumps virus (single-stranded RNA) is a member of the paramyxovirus group (genus Rubulavirus) and the etiologic agent of mumps in humans. Mumps is a generalized illness, usually accompanied by parotid (salivary gland) swelling and mild symptoms lasting 2 or more days. Parotitis as a presenting
symptom in mumps is usually sufficient to preclude confirmation by serology. However, one third of mumps infections are subclinical and may require viral isolation to confirm mumps infection. Infection with mumps virus, whether symptomatic or subclinical, is generally thought to offer lifelong immunity.

ELISA testing can be both specific and sensitive for the detection and measurement of serum proteins. Current methods for serodiagnosis of mumps include in vitro serum neutralization, hemagglutination inhibition (HAI), IFA, and CF. These test methods, however, lack specificity, which limits their usefulness in establishing immune status.

Reference Values

Normal

Negative for mumps IgG or IgM antibodies by ELISA: nonimmune Negative for viral antigen by RT-PCR

Positive for mumps IgG antibody: immune; indicates a current or previous exposure or immunization to mumps virus

Positive for mumps IgM antibody: indicates a current or recent infection

Procedure

Collect a 7-mL blood serum sample in a red-topped tube. The optimal time to collect serum in unvaccinated persons is 3 to 5 days after they become symptomatic. This is necessary because, in unvaccinated patients, IgM may not be present until 5 days after onset of symptoms, typically peaks in 7 days, and may be present for up to 6 weeks or more. Observe standard precautions. Place specimen in a biohazard bag for transport to the laboratory.
The CDC recommends that a blood specimen, buccal/oral swab, and urine be collected from individuals with clinical suspicion of mumps. Buccal/oral and urine specimens should be collected 3 to 5 days after the onset of symptoms. To collect the buccal/oral specimen, massage the parotid gland for 30 seconds and then swab the area between the cheek and gum by sweeping the swab near the upper to lower molar area.
Follow-up testing may be required.

Clinical Implications

When testing for IgG antibody, seroconversion between acute and convalescent sera is considered strong evidence of a current or recent infection.
The recommended interval between an acute and convalescent sample is 10 to 14 days.
The clinical case definition of mumps is an acute onset of unilateral or bilateral tender, self-limiting swelling of the parotid gland (or other salivary glands) with or without other apparent cause lasting 2 or more days. A probable case is one that meets the clinical case definition without serologic or virologic testing, whereas a confirmed case meets the clinical definition and is laboratory confirmed.

Interventions

Pretest Patient Care

Assess patient’s test knowledge. Explain test purpose and procedure.
Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

Interpret test outcome and counsel appropriately.
If there are no complications, typically, mumps is treated with bed rest and medications to reduce pain and fever, such as acetaminophen or nonsteroidal anti-inflammatory drugs (NSAIDs). Patients younger than 20 years should not be given aspirin because of its link to Reye’s syndrome.
Follow guidelines in Chapter 1 regarding safe, effective, informed posttest care.

Varicella-Zoster (Chickenpox) Antibody Test

Varicella-zoster virus (VZV) is a herpesvirus and causes chickenpox with primary infection, a highly contagious disease characterized by widely spread vesicular eruptions and fever. The disease is endemic in the United States and most commonly affects children 5 to 8 years of age, although adults and younger children, including infants, may develop chickenpox. VZV infection in a pregnant woman may spread through the placenta to the fetus, causing congenital disease in the infant.

Although a primary infection results in immunity to subsequent chickenpox, the virus remains latent in the body. When it is reactivated, VZV causes shingles (herpes zoster). The incubation period is 10 to 24 days. Fever and painful localized vesicular eruptions of the skin along the distribution of the involved nerves are the most common clinical symptoms.

The sensitivity, specificity, and reproducibility of ELISA immunoassays are comparable to other serologic tests for antibody such as IFA, CF, and HAI. A positive IgG result, coupled with a positive IgM result, indicates a current infection with VZV.

Reference Values

Normal

Negative for varicella-zoster IgG or IgM antibodies by ELISA: nonimmune

Positive for varicella-zoster IgG antibody: indicates a current or previous infection; in the absence of current clinical symptoms, may indicate immunity Positive for varicella-zoster IgM antibody; indicates a current or recent infection

Clinical Implications

When testing for IgG antibody, seroconversion between acute and convalescent sera is considered strong evidence of a current or recent infection. The recommended interval between an acute and convalescent sample is 10 to 14 days.
Whereas the presence of IgM antibody suggests a current or recent infection, low levels of IgM may occasionally persist for more than 12 months after infection or immunization.
Immunosuppressed patients in hospitals may contract severe nosocomial infections from others infected with VZV. Therefore, serologic screening of direct health care providers (e.g., physicians, nurses) is necessary to avoid spread of infection.

Interventions

Pretest Patient Care

Assess patient’s test knowledge. Explain test purpose and procedure. Advise pregnant women that VZV poses a high risk for congenital disease in the infant.
Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

Interpret test outcome and counsel appropriately. Inform patients who test positive for VZV IgG that they are naturally immune to chickenpox, but the virus can be reactivated and cause shingles at a later time.
Follow guidelines in Chapter 1 regarding safe, effective, informed posttest care.

Cytomegalovirus (CMV) Antibody Test

Cytomegalovirus (CMV) is a ubiquitous human viral pathogen that belongs to the herpesvirus family. Infection with CMV is usually asymptomatic (up to 60 days) and can persist in the host as a chronic or latent infection. Cytomegalovirus has been linked with sexually transmitted infections. Blood banks routinely screen for CMV antibodies and report these as CMV-negative or CMV-positive.

This test determines the presence of CMV antibodies and is routinely done in congenitally infected newborns, immunocompromised patients, and sexually active persons who present with mononucleosis-like symptoms. Antibody results must be evaluated in the context of the patient’s current clinical symptoms and viral culture results. Tests to detect CMV antigen are available and aid in early detection. Viral culture confirms CMV infection.

Reference Values

Normal

Negative for CMV-specific IgG and IgM by ELISA

Clinical Implications

Infants who acquire CMV during primary infection of the mother are prone to develop severe cytomegalic inclusion disease (CID). CID may be fatal or may cause neurologic sequelae such as mental retardation, deafness, microcephaly, or motor dysfunction.
Transfusion of CMV-infected blood products or transplantation of CMV-infected donor organs may produce interstitial pneumonitis in an immunocompromised recipient.
When testing for IgG antibody, seroconversion or a significant rise in titer between acute and convalescent sera may indicate presence of a current or recent infection.
Although the presence of IgM antibodies suggests current or recent infection, low levels of IgM antibodies may occasionally persist for more than 12 months after infection.

Herpes Simplex Virus (HSV) Antibodies (HSV-1 and HSV-2 Tests)

Two types of herpes simplex virus exist. Herpes simplex virus type 1 (HSV-1) causes orofacial herpes; type 2 (HSV-2) causes genital and neonatal herpes. Serologic differentiation is difficult; therefore, type-specific antibody tests are required.

These tests identify the herpes simplex infections. Human herpes simplex virus (HSV) is found worldwide and is transmitted by close personal contact. The clinical course is variable, and symptoms may be mild enough to go unrecognized. Major signs and symptoms include oral and skin eruptions, genital tract infections and lesions, and neonatal herpes. Herpes simplex is also common in individuals with immune system deficiencies (e.g., cancers, HIV/AIDS, chemotherapy treatment). HSV antibody testing is also widely used for bone marrow recipients and donors.

Reference Values

Normal

Negative for HSV-1 and HSV-2 by ELISA and IFA

Clinical Implications

Most persons in the general population have been infected with HSV by 20 years of age. After the primary infection, antibody levels fall and stabilize until a subsequent infection occurs.
Diagnosis of current infection is related to determining a significant increase in antibody titers between acute-stage and convalescent-stage blood samples.
Serologic tests cannot indicate the presence of active genital tract infections. Instead, direct examination with procurement of lesion cultures should be done.
Newborn infections are acquired during delivery through the birth canal and may present as localized skin lesions or more generalized organ system involvement.

Interventions

Pretest Patient Care

Assess patient’s knowledge regarding the test. Explain test purpose and procedure.
Follow guidelines in Chapter 1 regarding safe, effective, informed pretest care.

Posttest Patient Care

Interpret test outcome; see Interpreting Results of Immunologic Tests. Advise pregnant women that the newborn may be infected during birth when active genital area infection is present. Explain need for repeat testing.
Follow guidelines in Chapter 1 regarding safe, effective, informed posttest care.

Human T-Cell Lymphotropic Virus (HTLV-I/II) Antibody Test

This test detects antibodies to HTLV-I, a retrovirus associated with adult T-cell leukemia (ATL) and demyelinating neurologic disorders. The presence of HTLV-I antibodies in an asymptomatic person excludes that person from donating blood; however, this finding does not mean that leukemia or a neurologic disorder exists or will develop. Specimens with a positive test result by EIA are referred for Western blot. The results of Western blot are for investigational use only at the time of this printing.

Reference Values

Normal

Negative for HTLV-I/II antibodies by EIA and Western blot

Clinical Implications

Positive results (antibodies to HTLV-I) occur in the presence of HTLV-I infection. Infection transmitted to recipients of HTLV-I-infected blood is well documented.
The presence of antibodies to HTLV-I bears no relation to the presence of antibodies to HIV-1; its presence does not put a person at risk for HIV/AIDS, but they often occur concurrently because of similar risk factors.
HTLV-I is endemic to the Caribbean, Southeastern Japan, and some areas of Africa.
In the United States, HTLV-I has been detected in persons with ATL, intravenous drug users, and healthy persons as well as in donated blood products. Transmission can also take place through ingestion of breast milk, sexual contact, and sharing of contaminated intravenous drug paraphernalia.

Parvovirus B-19 Antibody Test

These antibody tests detect parvovirus B-19, the only parvovirus known to cause human disease. The B-19 virus destroys red blood cell precursor cells and interferes with normal red blood cell production. In young children, it is associated with erythema infectiosum, a mild, self-limited disease characterized by a low-grade fever and rash. Recently, it has been associated with aplastic crisis in patients with chronic hemolytic anemia and in immunodeficient patients who have bone marrow failure.

Reference Values

Normal

Negative for parvovirus B-19-specific IgG and IgM antibodies by ELISA and IFA

Interventions

Pretest Patient Care

Assess patient’s knowledge regarding test. Explain purpose and blood test procedure. Advise any prospective organ donor that this test is part of a panel of tests performed before organ donation to protect the organ recipient from potential infection.
Follow guidelines in Chapter 1 regarding safe, effective, informed pretest care.

Posttest Patient Care

Interpret test outcome (see Interpreting Results of Immunologic Tests) and explain significance of results.
Follow guidelines in Chapter 1 regarding safe, effective, informed posttest care.

Rabies Antibody Tests

Rabies, a viral infection, is transmitted in the saliva of infected animals, such as bats, raccoons, skunks, cats, and dogs. Serologic testing is diagnostic for the presence of rabies in animals. It also indicates the degree of antibody responses to rabies immunization (e.g., for people who routinely work with animals).

Reference Values

Normal

IFA <1:16 or direct fluorescent antibody (DFA) examination of the animal brain for presence of the virus

Clinical Implications

An elevated titer in humans indicates an adequate response after immunization. A rabies titer of 1:16 or greater is considered protective.
Pre-exposure vaccination should be offered to individuals in high-risk groups, such as veterinarians, animal handlers, or international travelers if they are likely to come in contact with rabid animals and medical care is limited.
Postexposure vaccination should be administered to previously vaccinated individuals if exposed to rabies.
Postexposure prophylaxis is considered a medical urgency, and each situation should be evaluated by trained medical personnel and in consultation with public health officials. The individual should not be vaccinated unless the animal develops clinical signs of rabies during a 10-day observation period. If the animal is rabid, the person should be vaccinated immediately.

FUNGAL TESTS

Fungal Antibody Tests: Histoplasmosis, Blastomycosis, Coccidioidomycosis

Certain fungal species are associated with human respiratory diseases acquired by inhaling spores from sources such as dust, soil, and bird droppings. Serologic tests may be used for diagnosis. Fungal diseases are categorized as either superficial or deep. For the most part, superficial mycoses are limited to the skin, mucous membranes, nails, and hair. Deep mycoses involve the deeper tissues and internal organs. Histoplasmosis, coccidioidomycosis, and blastomycosis are caused by deep mycoses.

These tests detect serum precipitin antibodies and CF antibodies present in the fungal diseases of coccidioidomycosis, blastomycosis, and histoplasmosis. Coccidioidomycosis, also known as desert fever, San Joaquin fever, and valley fever, is contracted through inhalation of Coccidioides immitis spores found in dust or soil. Blastomycosis is caused by infection with organisms of the genus Blastomyces. Histoplasmosis is a granulomatous infection caused by Histoplasma capsulatum.

Reference Values

Normal

Negative for fungal antibodies CF titer: <1:8 Immunodiffusion: negative

Interfering Factors

Antibodies to fungi may be found in blood samples from apparently healthy people.
When testing for blastomycosis, cross-reactions with histoplasmosis may occur.
More than 50% of patients having active blastomycosis yield a negative result by CF.
Recent histoplasmosis skin tests must be avoided because they cause elevated CF test results, which may be due to the stimulation from the skin test and not the systemic infection.

Candida Antibody Test

Candidiasis is usually caused by Candida albicans and affects the mucous membranes, skin, and nails (see Candida Skin Test). Compromised individuals with depressed T-cell function are most likely to have invasive disease.

Identifying the Candida antibody can be helpful when the diagnosis of systemic candidiasis cannot be shown by culture or tissue sample. Clinical symptomatology must be present for the test to be meaningful. Tests used include immunodiffusion; counterimmunoelectrophoresis (CIE), which is particularly valuable on CSF and urine specimens; and latex agglutination for Candida antigen.

Reference Values

Normal

Negative for Candida antibodies by immunodiffusion (ID)

Clinical Implications

A titer ≥1:8 by latex agglutination (LA) or CIE for Candida antigen indicates systemic infection.
A fourfold rise in titers of paired blood samples 10 to 14 days apart indicates acute infection.
Patients on long-term intravenous therapy treated with broad-spectrum antibiotics and diabetic patients commonly have disseminated infections caused by Candida albicans. The disease also occurs in bottle-fed newborns and in the urinary bladder of catheterized patients.
Vulvovaginal candidiasis, common in late pregnancy, can transmit candidiasis to the infant through the birth canal.

Interfering Factors

Approximately 25% of the normal population tests positive for the presence of Candida.
Cross-reaction can occur with latex agglutination testing in persons who have cryptococcosis or tuberculosis.
Positive results can occur in the presence of mucocutaneous candidiasis or severe vaginitis.

Aspergillus Antibody Test

The aspergilli, especially Aspergillus fumigatus, Aspergillus flavus, and Aspergillus niger, are associated with pulmonary infections and invasive fatal disease sequelae in immunosuppressed patients. Manifestations of Aspergillus infections include allergic bronchopulmonary disease, lung mycetoma, endophthalmitis, and disseminated brain, kidney, heart, and bone disease.

This test detects antibodies present in aspergillosis, primarily allergic bronchopulmonary disease, or fungus ball.

Reference Values

Normal

Negative for Aspergillus antibody by immunodiffusion <1:8 by CF

Cryptococcus Antibody Test

Cryptococcus neoformans, a yeast-like fungus, causes a lung infection thought to be acquired by inhalation. The organism has been isolated from several natural environments, especially where weathered pigeon droppings accumulate.

This test detects antibodies present in Cryptococcus infections. It appears that about 50% of patients who present with antibodies have a predisposing condition such as lymphoma or sarcoidosis
or are being treated with steroid therapy. Infection with C. neoformans has long been associated with Hodgkin’s disease and other malignant lymphomas. In fact, C. neoformans, in conjunction with malignancy, occurs to such a degree that some researchers have raised the question regarding the possible etiologic relation between the two diseases. Tests ordered for this disease include latex agglutination testing for antigens or antibodies.

Reference Values

Normal

Negative for Cryptococcus antibody by IFA or tube agglutination (TA) IFA test has a specificity of 77%. TA test has a specificity of 89%.

Tags: Manual of Laboratory and Diagnostic Tests A

Jun 11, 2016 | Posted by drzezo in PATHOLOGY & LABORATORY MEDICINE | Comments Off

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