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 (SRDs), such as rheumatoid arthritis (RA) 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., 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, cerebrospinal fluid [CSF]).
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.
Perform the serologic test before doing skin testing. Skin testing often induces antibody production and could interfere with serologic test results.
Label the specimen with the patient’s name, date, and tests ordered and place in a 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:
History of previous infection by the same organism
Previous vaccination (determine time frame)
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.
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).
Presence of other serious illness states (e.g., lack of immunologic response in agammaglobulinemia, cancer treatment with immunosuppressant drugs)
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 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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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.
Normal Findings
Nonreactive, negative for syphilis
TABLE 8.2 Sensitivity of Commonly Used Serologic Tests for Syphilis | ||||||||||||||||||||||||||||||||||||||
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TABLE 8.3 Nonsyphilitic Conditions Giving Biologic False-Positive Results Using Venereal Disease Research Laboratory and Rapid Plasma Reagin Tests | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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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%
NOTE
A reactive RPR or VDRL test should be confirmed with an FTA-ABS or TP-PA.
Procedure
Collect a 7-mL blood serum sample in a red-topped tube. Observe standard precautions. Fasting is usually not required.
Label the specimen with the patient’s name, date, and tests ordered and place in a biohazard bag for transport to the laboratory.
PROCEDURAL ALERTIf the RPR test is used, the following need to be observed:
Excess chyle released into the blood during digestion interferes with test results; therefore, the patient should fast for 8 hr.
Alcohol decreases reaction intensity in tests that detect reagin; therefore, alcohol ingestion should be avoided for at least 24 hr before blood is drawn.
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 for safe, effective, informed pretest care.
Posttest Patient Care
Review test results; report and record findings. Modify the nursing care plan as needed. Counsel the patient regarding abnormal findings. Explain biologic false-positive or false-negative reactions. Explain the need for possible follow-up testing.
Follow guidelines in Chapter 1 for safe, effective, informed posttest care.
CLINICAL ALERT
Sexual partners of patients with syphilis should be evaluated for the disease.
After treatment, patients with early-stage syphilis should be tested at 3-mo intervals for 1 yr to monitor for declining reactivity.
• 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 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. Immunoglobulin G (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.
Normal Findings
Negative for both IgG and IgM Lyme antibodies by ELISA and Western blot
Procedure
Collect a 7-mL blood serum sample in a red-topped tube. CSF may also be used for the test.
Observe standard precautions. Label the specimen with the patient’s name, date, and tests ordered and place in a biohazard bag.
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 for safe, effective, informed pretest care.
Posttest Patient Care
Review test results; report and record findings. Modify the nursing care plan as needed. Explain the need for possible follow-up treatment and testing 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 for 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.
Normal Findings
Negative for Legionnaires’ disease by indirect fluorescent antibody (IFA) test or ELISA
Procedure
Collect a 7-mL blood serum sample in a red-topped tube. Observe standard precautions. Label the specimen with the patient’s name, date, and tests ordered and place in a biohazard bag for transport to the laboratory.
Follow-up testing is usually requested 3 to 6 weeks after initial symptom appearance.
Alert the patient that a urine specimen may be required if antigen testing is indicated.
Clinical Implications
A dramatic rise of titer levels to more than 1:128 in the interval between acute- and convalescentphase 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.
Interventions
Pretest Patient Care
Assess clinical history and knowledge about the test. Explain purpose and procedure of blood test.
Follow guidelines in Chapter 1 for safe, effective, informed pretest care.
Posttest Patient Care
Review test results; report and record findings. Modify the nursing care plan as needed. Counsel the patient regarding abnormal findings; explain the need for possible follow-up testing, because negative results do not rule out L. pneumophila.
Follow guidelines in Chapter 1 for safe, effective, informed posttest care.
• Chlamydia Nucleic Acid Amplification Test (NAAT)
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, and 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, and reporting has been required in all 50 states and the District of Columbia since 2000. The national infection rate for C. trachomatis has increased from 2000 to 2015, with the exception of a slight decrease during 2011 to 2013. In 2015, there were 478.8 reported cases per 100,000 people.
Screening for chlamydia is particularly important because it is such a common sexually transmitted disease (STD), which is often asymptomatic, but which can cause serious complications if left untreated. Annual screening for chlamydia is recommended for all sexually active women under the age of 25, for women older than 25 if they have new or multiple sex partners or a sex partner with a diagnosed STD, and for men who have sex with other men. Pregnant women who are at risk should also be screened for chlamydia early in pregnancy.
Although methods such as culture, direct fluorescent antibody stain and DNA probe are available to test for chlamydia, the nucleic acid amplification test (NAAT) (which detects the genetic material of chlamydia trachomatis), is recommended because it is more sensitive and specific and can be done without a pelvic exam for women.
Normal Findings
Negative for chlamydia DNA
Procedure
For females:
Use a collection swab with a plastic or wire shaft and rayon, dacron or cytobrush tip to swab the vagina.
Use a sucrose phosphate glutament buffer or M4 media to store and transport the specimen to the lab at ≤4 °C within 24 hours. If the sample cannot be transported to the lab within 24 hours, store at -70 °C.
For males:
Obtain a first morning urine sample.
Place specimen in a biohazard bag for transport to the laboratory.
Clinical Implications
The NAAT test detects the presence of chlamydia DNA, but does not measure whether antibiotic treatment is effective. In those cases, bacterial culture using antibody testing is needed to determine the correct antibiotic therapy.
Interventions
Pretest Patient Care
Assess patient knowledge regarding the test and explain purpose and procedure. Elicit history regarding possible exposure to organism.
Follow guidelines in Chapter 1 for safe, effective, informed pretest care.
Posttest Patient Care
Review test results; report and record findings. Modify the nursing care plan as needed.
Follow guidelines in Chapter 1 for safe, effective, informed posttest care.
• 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.
Normal Findings
ASO titer:
Adult: <160 Todd units/mL or <200 IU Child (5 to 12 years of age): 170 to 330 Todd units/mL
ADB: A negative test is normal.
Preschool-age children: <60 Todd units/mL
School-age children: <170 Todd units/mL
Adults: <85 Todd units/mL
Streptozyme: negative for streptococcal antibodies
Procedure
Collect a 7-mL blood serum sample in a red-topped tube. Observe standard precautions. Label the specimen with the patient’s name, date, and tests ordered and place in a biohazard bag for transport to the laboratory.
Repeat testing is recommended 10 days after the first test.
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.
CLINICAL ALERTThe ASO test is impractical in patients who have recently received antibiotics or who are scheduled for antibiotic therapy because the treatment suppresses the antibody response.
Interventions
Pretest Patient Care
Assess patient’s clinical history and test knowledge. Explain test purpose and procedure.
Follow guidelines in Chapter 1 for safe, effective, informed pretest care.
Posttest Patient Care
Review test results; report and record findings. Modify the nursing care plan as needed. Counsel the patient regarding abnormal findings; explain the need for possible follow-up testing. See Interpreting Results of Immunologic Tests on page 537.
Follow guidelines in Chapter 1 for safe, effective, informed posttest care.
• Helicobacter pylori (HPY) IgG Antibody Serum, Stool, and Breath (PY) Test
Helicobacter pylori (previously known as Campylobacter pylori) is a bacterium associated with gastritis, duodenal and gastric ulcers, and possibly gastric carcinoma. The healthcare provider 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%.
Normal Findings
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 to 199 DPM indeterminate for H. pylori
>200 DPM positive for H. pylori
Procedure
Collect a 7-mL blood serum sample in a red-topped tube. Observe standard precautions. Label the specimen with the patient’s name, date, and test(s) ordered and place 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.
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.
The 13C-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, and 13CO2 levels are assessed using isotope ratio mass spectrometry.
PROCEDURAL ALERT
The patient should have no antibiotics and bismuth for 1 mo and no proton pump inhibitors and sucralfate for 2 wk before test.
Instruct the patient not to chew the capsule.
The patient should be at rest during breath collection.
Clinical Implications
This assay is intended for use as an aid in the diagnosis of H. pylori, and additionally, false-negative results may occur. The clinical diagnosis should not be based on serology alone but rather on a combination of serology (and breath or stool tests), symptoms, and gastric biopsy-based tests as warranted.
The stool antigen test is used to monitor response during therapy and to test for cure after treatment.
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, and 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 for safe, effective, informed pretest care.
Posttest Patient Care
Review test results; report and record findings. Modify the nursing care plan as needed. Counsel the patient regarding abnormal findings; explain the need for possible follow-up testing and treatment, which may entail 4 to 6 weeks of antibiotics to eradicate H. pylori and medication to suppress acid production. Many persons may be infected with H. pylori but are asymptomatic.
Follow guidelines in Chapter 1 for 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.
Normal Findings
Negative for IM by latex agglutination (LA)
Negative for EBV antibodies by IFA or ELISA
NOTE
Heterophile antibodies are present within 14 to 21 days in 60% of patients and within 30 days in 85% of patients.
Procedure
Collect a 7-mL blood serum sample in a red-topped tube. Observe standard precautions.
Label the specimen with the patient’s name, date, and tests ordered and place in a biohazard bag for transport to the laboratory.
Clinical Implications
The presence of heterophile antibodies (Monospot), along with clinical signs and other hematologic findings, is diagnostic for IM.
Heterophile antibodies remain elevated for 8 to 12 weeks after symptoms appear.
Approximately 90% of adults have antibodies to the virus.
The Monospot test is negative more frequently in children and almost uniformly in infants with primary EBV infection.
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 for safe, effective, informed pretest care.
Posttest Patient Care
Review test results; report and record findings. Modify the nursing care plan as needed.
Counsel the patient regarding abnormal findings; explain the need for possible follow-up testing and treatment, such as intravenous fluids. See Interpreting Results of Immunologic Tests on page 537.
Tell the patient that, after primary exposure, a person is considered immune. Recurrence of IM is rare.
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 for 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: <0.01 pg/mL for viral load. Detection of hepatitis B 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., needlesticks, 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 ultrasensitive quantitative PCR is the most sensitive test available for hepatitis B viral load.
TABLE 8.4 Hepatitis Test Findings in Various Stages | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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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 HCV (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.
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 HEV (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
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
TABLE 8.5 Summary of Clinical and Epidemiologic Features of Viral Hepatitis Agents | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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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
Healthcare workers
Susceptible individuals with chronic liver disease
Indications for Hepatitis B Vaccine
Family members of adoptees from foreign countries who are HBsAg-positive
Healthcare workers and trainees in healthcare 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; healthcare workers, recipients of clotting factors, and 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 HBsAgpositive.
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.
Normal Findings
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. Label the specimen with the patient’s name, date, and test(s) ordered and place 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.
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
Multiple sexual partners, 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 highrisk group to date
Hepatitis G
Blood
Unknown
Occurs with hepatitis B and hepatitis C
Recipient of contaminated blood
ELISA, enzyme-linked immunosorbent assay; HBcAg, hepatitis B core antigen; HBsAg, hepatitis B surface antigen; HBV, hepatitis B; IgM, immunoglobulin M; PCR, polymerase chain reaction.
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 herpesvirus 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
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 healthcare 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); in addition, infants born to infected mothers (during delivery), hemodialysis patients, and healthcare employees are at higher risk for infection. Of all persons with HBV infection, 38% to 40% contract HBV during early childhood.
Healthcare 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.
TABLE 8.8 Markers That Appear After Infection | ||||||||||||||||||||||||||||||||||||
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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 for safe, effective, informed pretest care.
Posttest Patient Care
Review test results; report and record findings. Modify the nursing care plan as needed. Explain significance of test results and counsel appropriately regarding presence of infection, recovery, and immunity.
Counsel healthcare workers and family regarding protective and preventive measures necessary to avoid transmission.
Instruct patients to alert healthcare 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 for safe, effective, informed posttest care.
CLINICAL ALERT
Observe enteric and standard precautions for 7 d 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 mo. Transfusionacquired hepatitis may not show up for 6 mo 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 hr of skin-break contact and within 14 d of last sexual contact. For hepatitis A, immune globulin (IG) should be given within 2 wk of exposure. In day care centers, IG should be given to all contacts (children and personnel).
• HIV-1/2 Tests
Infection with HIV-1 is most prevalent in the United States and Western Europe. HIV-1 p24 antigen is a viral protein that is present in high amounts in individuals who are newly infected. A combination immunoassay is used to detect HIV-1 and HIV-2 antibodies, as well as HIV-1 p24 antigen (referred to as 4th generation testing). If a specimen is reactive on the initial immunoassay, then additional testing will take place to differentiate between HIV-1 and HIV-2 antibodies. If the results of the additional testing are either nonreactive or indeterminate, then HIV-1 nucleic acid testing (NAT) will be done. This test process provides the foundation for identifying acute and established HIV-1 infections, providing more accurate diagnosis of HIV-2 infection and timely reporting of test results to public health entities. After identification and differentiation of HIV-1 and HIV-2 antibodies, additional tests such as HIV-1 viral load, CD4+T-lymphocyte, and antiretroviral resistance assay are necessary to confirm infection, determine the stage of HIV disease and tailor treatment (Table 8.9). Most cases associated with HIV-2 are reported in West Africa.
Normal Findings
Negative for HIV antibodies and antigens
Procedure
Serum Testing
Use a special testing kit such as the FDA-approved commercial Alere Determine HIV-1/2 Ag/Ab Combo. The kit includes a specially treated sample pad, to which a whole blood (from
venipuncture or fingerstick), serum or plasma specimen is applied. A Chase Buffer is applied to whole blood samples, and the test results are read between 20 and 30 minutes after application of the Chase Buffer.
Interpret the results according to the manufacturer’s guidelines and instructions.
TABLE 8.9 Diagnostic Testing for HIV | |||||||||
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Clinical Implications
An antibody reactive test is associated with the detection of HIV-1 and/or HIV-2 antibodies in the specimen, and an antigen reactive test is associated with the detection of HIV-1 p24 antigen in the specimen.
The presence of HIV-1/2 antibodies or HIV-1 p24 antigen is presumptive for HIV infection.
A nonreactive test result does not preclude the possibility of an HIV exposure or infection.
Reactive test results should be followed by further confirmatory testing.
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.
Interfering Factors
Test kits require the use of specific specimens. Refer to test kit instructions to verify that the proper specimen type is being used; otherwise, the kit may produce inaccurate results. Timing of appearance of viral and serologic markers varies (see Fig. 8.1)
 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 102(5B):117-124, 1997. 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 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 for 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 healthcare facility must determine how best to accomplish this.
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