Diagnostic Testing



Diagnostic Testing






OVERVIEW OF LABORATORY AND DIAGNOSTIC TESTING

Healthcare delivery is a complex system that involves many different disciplines and specialties, with care provided in a variety of settings. Consequently, healthcare providers must have an understanding and working knowledge of modalities beyond their own area of expertise. This includes diagnostic evaluation and diagnostic services.

Laboratory and diagnostic tests are tools to gain additional information about the patient. By themselves, these tests are not therapeutic; however, when used in conjunction with a thorough history and physical examination, these tests may confirm a diagnosis or provide valuable information about a patient’s status and response to therapy that may not be apparent from the history and physical examination alone.

Table 1.1 lists the reasons for laboratory and diagnostic testing and examples of tests selected for each purpose. As an integral part of their practice, healthcare providers support patients and their family members in meeting the demands and challenges incumbent in the simplest to the most complex diagnostic testing. This testing begins before birth in the form of prenatal ultrasounds, genetic testing, and amniocentesis and frequently continues after death in the case of postmortem testing for evidentiary or forensic purposes, organ transplantation, or death reporting (autopsy).

The healthcare provider who provides diagnostic services must have basic requisite knowledge to plan patient care and an understanding of psychoneuroimmunology (effects of stress on health status). He or she must be able to make careful judgments and gather vital information about the patient and the testing process to diagnose appropriately within the parameters of the healthcare provider’s professional standards.


The Diagnostic Testing Model

The diagnostic testing model incorporates three phases: pretest, intratest, and posttest. Figure 1.1 provides an overview of the responsibilities of the healthcare provider before, during, and after testing.


The later parts of this chapter address the interventions and knowledge required by healthcare providers in each phase of the test process.




Clinical Value of a Test

The clinical value of a test is related to its sensitivity, its specificity, and the incidence of the disease in the population tested.



  • Specificity refers to the ability of a test to correctly identify individuals who do not have the disease. The formula for specificity is as follows:









FIGURE 1.1. A model for the role of the clinical team in diagnostic care and services. Diagnostic care and services are performed safely and effectively in all three phases. S.O., significant others.










TABLE 1.2 Standards for Diagnostic Evaluation



































Source of Standards for Diagnostic Service


Standards for Diagnostic Testing


Examples of Applied Standards for Diagnostic Testing


Professional practice parameters of American Nurses Association (ANA), American Medical Association (AMA), American Society for Clinical Pathology (ASCP), American College of Radiology, Centers for Disease Control and Prevention (CDC), and The Joint Commission healthcare practice requirements


Use a model as a framework for choosing the proper test or procedure and to interpret test results. Use laboratory and diagnostic procedures for screening, differential diagnoses, follow-up, and case management.


Test strategies include single tests or combinations or panels of tests. Panels can be performed in parallel, as a series, or both. Patient education and proper patient preparation are involved.


The guidelines of the major agencies, such as American Heart Association (e.g., stress tests after abnormal electrocardiogram [ECG]), American Cancer Society (e.g., colonoscopy for colon cancer), and American Diabetes Association (e.g., hemoglobin A1c <7% for diabetes)


Order the correct test; appropriately collect and transport specimens. Properly perform tests in an accredited laboratory or diagnostic facility. Accurately report test results. Communicate and interpret test findings. Treat or monitor the disease and the course of therapy. Provide diagnosis as well as prognosis.


Patients receive diagnostic services based on a documented assessment of need for diagnostic evaluation. Patients have the right to receive information about the benefits and risks of testing so they can make informed decisions that reflect their needs and desires for diagnostic care.


Individual agency and institution standards:




  • Policies, procedures, and quality control criteria for specimen collection



  • Procedure statement for monitoring the patient after an invasive procedure



  • Policy for universal witnessed consent situations



  • Statements on quality improvement standards



  • Standards of professional practice and standards of patient care



  • Policy for obtaining informed consent or witnessed consent



  • Policies for unusual situations


Observe standard precautions (formerly known as universal precautions). Use latex allergy protocols and required methodology of specimen collection. Use standards and statements for monitoring patients who receive sedation and analgesia. Vital signs are monitored and recorded at specific times before and after the procedure. Patients are monitored for bleeding and respiratory or neurovascular changes. Record data regarding outcomes when defined care criteria are implemented and practiced. Protocols to obtain appropriate consents are employed, and deviations from basic consent policies are documented and reported to the proper individual.


The healthcare provider wears protective eyewear and gloves when handling all body fluids and employs proper handwashing before and after handling specimens and between patient contacts. Labeled biohazard bags are used for specimen transport. Vital signs are monitored and recorded at specific times before and after the procedure. Patients are monitored for bleeding and respiratory or neurovascular changes. Record data regarding outcomes when defined care criteria are implemented and practiced. Protocols to obtain appropriate consents are employed, and deviations from basic consent policies are documented and reported to the proper individual.


State and federal government communicable disease reporting regulations: Centers for Disease Control and Prevention (CDC), U.S. Department of Health & Human Services, Agency for Healthcare Research and Quality (AHRQ), and Clinical Laboratory Improvement Act (CLIA)


Clinical laboratory personnel and other healthcare providers follow regulations to control the spread of communicable diseases by reporting certain disease conditions, outbreaks, and unusual manifestations, morbidity, and mortality data. Findings from research studies provide healthcare policy makers with evidence-based guidelines for appropriate selection of tests and procedures.


The healthcare provider reports laboratory evidence of certain disease classes (e.g., sexually transmitted diseases, diphtheria, Lyme disease, symptomatic HIV infection; see list of reportable diseases). Personnel with hepatitis A may not handle food or care for patients, young children, or elderly people for a specific period of time. Federal government regulates shipment of diagnostic specimens. Magnetic resonance imaging and computed tomography are used to evaluate persistent low back pain according to AHRQ guidelines.


U.S. Department of Transportation


Alcohol testing is done in emergency departments in special situations (e.g., following a motor vehicle crash, homicide, or suicide or in an unconscious individual).


Properly trained personnel perform blood, saliva, and breath alcohol testing and use required kits as referenced by federal law.


Occupational Safety and Health Administration (OSHA)


The healthcare provider is properly trained, under mandated guidelines, to administer employee medical surveillance.


Properly trained personnel perform respirator qualification, fit testing, and monitoring for toxic exposure.


Clinical and Laboratory Standards Institute (CLSI)


Develops standards and guidelines for laboratory testing. Standards define specific materials, methods, and practices as they relate to laboratory specimen tests. Guidelines describe essential criteria for a procedure that can be modified by the user to fit his or her needs.


Provides healthcare professionals with practical guidelines for consistency in procedural methods in laboratory testing.










CHART 1.1 Grading Guidelines for Scientific Evidence























Grade


Guideline


Example


A


Clear evidence from all appropriately conducted trials


Measure plasma glucose through an accredited lab to diagnose or screen for diabetes


B


Supportive evidence from wellconducted studies or registries


Draw fasting blood plasma specimens for glucose analysis


C


No published evidence; or only case, observational, or historical evidence


Self-monitoring of blood glucose may help to achieve better control


E


Expert consensus or clinical experience or Internet polls


Measure ketones in urine or blood to monitor and diagnose diabetic keto acidosis (DKA) (in home or clinic)




  • Sensitivity refers to the ability of a test to correctly identify individuals who have the disease. The formula for sensitivity is as follows:





  • True positive: positive test result in a person with the disease


  • True negative: negative test result in a person without the disease


  • False positive: positive test result in a person without the disease


  • False negative: negative test result in a person with the disease

Sensitivity and specificity do not change with different populations of ill and healthy patients.



  • Incidence refers to the number of new cases of a disease, during a specified period of time, in a specified population or community.


  • Prevalence refers to the number of existing cases of a disease, at a specific period of time, in a given population.


  • Predictive values refer to the ability of a screening test result to correctly identify the disease state. The predictive value of a test can be very different when applied to people of differing ages, gender, geographic locations, and cultures. True-positive results correctly identify individuals who actually have the disease, and true-negative results correctly identify individuals who do not actually have the disease. Positive predictive value equals the percentage of positive tests with true-positive results (i.e., the individual does have the disease). Negative predictive value refers to the percentage of negative tests with true-negative results (i.e., the individual does not have the disease).



See Table 1.3 for an example that demonstrates the specificity, sensitivity, and predictive values for a screening test to identify the cystic fibrosis gene.










TABLE 1.3 Sample Test Results























Test Result


Have Gene for Cystic Fibrosis


Do Not Have Gene for Cystic Fibrosis


Total


Positive


62


5


67


Negative


15


341


356


TOTAL


77


346


423



Thus, this screening test will give a false-negative result about 20% of the time (e.g., the person does have the cystic fibrosis gene but his or her test results are negative).


Thus, there is an 8% chance that the person will test positive for the cystic fibrosis gene but does not have it.


Thus, there is a 5% chance that the person will test negative for the cystic fibrosis gene but actually does have it.



DIAGNOSTIC TESTING AND THE HEALTHCARE DELIVERY SYSTEM


Testing Environments

Diagnostic testing occurs in many different environments. Many test sites have shifted into community settings and away from hospitals and clinics.



  • Point-of-care testing (POCT) refers to medical testing done in close proximity to the site of patient care (e.g., in the primary care setting or acute care settings [emergency department, critical care units, ambulances]), thus moving toward decentralized testing. POCT is convenient for the patient, produces rapid reporting of test results, and allows for more timely assessment, management, and treatment.


  • Testing in the home care environment requires skill in procedures such as drawing blood samples, collecting specimens from retention catheters, proper labeling, handling, and transporting of specimens, and documentation. Moreover, teaching the patient and family members how to collect specimens is an important part of the process.











TABLE 1.4 Examples of Conversions to Système International (SI) Units




































































































































































































































































































































































































































































































































































































































































Component


System


Conventional U.S. Reference Intervals


Conventional U.S. Unit


Conversion Factor


SI Reference Intervals


SI Unit Symbol


Alanine aminotransferase (ALT)


Serum


5-40


U/L


1.00


5-40 U/L


Albumin


Serum


3.9-5.0


g/dL


10


39-50


g/L


Alkaline phosphatase


Serum


35-110


U/L


0.01667


0.6-1.8


μkat/L


Aspartate aminotransferase (AST)


Serum


5-40


U/L


0.01667


0.08-0.67


μkat/L


Bilirubin


Serum



Direct



0-0.2


mg/dL


17.10


0-4


μmol/L



Total



0.1-1.2


mg/dL


17.10


2-20


μmol/L


Calcium


Serum


8.6-10.3


mg/dL


0.2495


2.15-2.57


mmol/L


Carbon dioxide, total


Serum


22-30


mEq/L


1.00


22-30


mmol/L


Chloride


Serum


98-108


mEq/L


1.00


98-108


mmol/L


Cholesterol


Serum



Age <29 yr



<200


mg/dL


0.02586


<5.15


mmol/L



30-39 yr



<225


mg/dL


0.02586


<5.80


mmol/L



40-49 yr



<245


mg/dL


0.02586


<6.35


mmol/L



>50 yr



<265


mg/dL


0.02586


<6.85


mmol/L


Complete blood count


Blood


Hematocrit



Men



42-52


%


0.01


0.42-0.52


1



Women



37-47


%


0.01


0.37-0.47


1


Red cell count


Blood



Men



4.6-6.2 × 106


/mm3


106


4.6-6.2 × 1012/L



Women



4.2-5.4 × 106


/mm3


106


4.2-5.4 × 1012/L



White cell count



4.5-11.0 × 103


/mm3


106


4.5-11.0 × 109/L



Platelet count



150-300 × 103


/mm3


106


150-300 × 109/L


Cortisol


Serum



8 am



5-25


μ/dL


27.59


140-690


nmol/L



8 pm



3-13


μg/dL


27.59


80-360


nmol/L


Cortisol


Urine


20-90


μg/24 hr


2.759


55-250


nmol/24 hr


Creatine kinase (CK)


Serum



High CK group (black men)



50-250


U/L


1.00


50-250


U/L



Intermediate CK group (nonblack men, black women)



35-345


U/L


1.00


35-345


U/L



Low CK group (nonblack women)



25-145


U/L


1.00


25-145


U/L


Creatinine kinase isoenzyme, MB fraction


Serum


>5


%


0.01


>0.05


1


Creatinine


Serum


0.4-1.3


mg/dL


88.40


35-115


μmol/L



Men



0.7-1.3


mg/dL


88.40


62-115


μmol/L



Women



0.4-1.1


mg/dL


88.40


35-97


μmol/L


Digoxin, therapeutic


Serum


0.5-2.0


ng/mL


1.281


0.6-2.6


nmol/L


Erythrocyte indices


Blood


Mean corpuscular volume (MCV)



80-100


microns3


1.00


80-100


fL


Mean corpuscular hemoglobin (MCH)



27-31


pg


1.00


27-31


pg


Mean corpuscular hemoglobin concentration (MCHC)



32-36


%


0.01


0.32-0.36


1


Ferritin


Serum



Men



29-438


ng/mL


1.00


29-438


μg/L



Women



9-219


ng/mL


1.00


9-219


μg/L


Folate


Serum


2.5-20.0


ng/mL


2.266


6-46


nmol/L


Follicle-stimulating hormone (FSH)


Serum



Children



≤12


mIU/mL


1.00


≤12


IU/L



Men



2.0-10.0


mIU/mL


1.00


2.0-10.0


IU/L



Women, follicular



3.2-9.0


mIU/mL


1.00


3.2-9.0


IU/L



Women, midcycle



3.2-9.0


mIU/mL


1.00


3.2-9.0


IU/L



Women, luteal



2.0-6.2


mIU/mL


1.00


2.0-6.2


IU/L


Gases, arterial


Blood



PO2



80-95


mm Hg


0.1333


10.7-12.7


kPa



PCO2



37-43


mm Hg


0.1333


4.9-5.7


kPa


Glucose


Serum


62-110


mg/dL


0.05551


3.4-6.1


mmol/L


Iron


Serum


50-160


μg/dL


0.1791


9-29


μmol/L


Iron-binding capacity


Serum



Total iron-binding capacity



230-410


μg/dL


0.1791


41-73


μmol/L



Saturation



15-55


%


0.01


0.15-0.55


1


Lactate dehydrogenase


Serum


120-300


U/L


1.00


120-300


U/L


Luteinizing hormone


Serum



Men



4.9-15.0


mIU/mL


1.00


4.9-15.0


IU/L



Women, follicular



5.0-25


mIU/mL


1.00


5.0-25


IU/L



Women, luteal



3.1-13


mIU/mL


1.00


3.1-13


IU/L


Magnesium


Serum


1.2-1.9


mEq/L


0.4114


0.50-0.78


mmol/L


Osmolality


Serum


278-300


mOsm/kg


1.00


278-300


mmol/kg


Osmolality


Urine


None defined


mOsm/kg


1.00


None defined


mmol/kg


Phenobarbital, therapeutic


Serum


15-40


μg/mL


4.306


65-175


μmol/L


Phenytoin, therapeutic


Serum


10-20


μg/mL


3.964


40-80


μmol/L


Phosphate (phosphorus, inorganic)


Serum


2.3-4.1


mg/dL


0.3229


0.75-1.35


mmol/L


Potassium


Serum


3.7-5.1


mEq/L g/mL


1.00


3.7-5.1


mmol/L


Protein, total


Serum


6.5-8.3


g/dL


10.0


65-83


g/L


Sodium


Serum


134-142


mEq/L


1.00


134-142


mmol/L


Theophylline, therapeutic


Serum


5-20


μg/mL


5.550


28-110


μmol/L


Thyroid-stimulating hormone (TSH)


Serum


0-5


μIU/mL


1.00


0-5


mIU/L


Thyroxine


Serum


4.5-13.2


μg/dL


12.87


58-170


nmol/L


T3-uptake ratio


Serum


0.88-1.19


1


1.00


0.88-1.19


1


Triiodothyronine (T3)


Serum


70-235


ng/mL


0.01536


1.1-3.6


nmol/L


Triglycerides


Serum


50-200


mg/dL


0.01129


0.55-2.25


mmol/L


Urate (uric acid)


Serum



Men



2.9-8.5


mg/dL


59.48


170-510


μmol/L



Women



2.2-6.5


mg/dL


59.48


130-390


μmol/L


Urea nitrogen


Serum


6-25


mg/dL


0.3570


2.1-8.9


mmol/L


Vitamin B12


Serum


250-1000


pg/mL


0.7378


180-740


pmol/L


Source: Blair ER (ed.): Damon Clinical Laboratories Handbook. Stow, OH, Lexi-Comp, 1989.





  • In occupational environments, testing may be done to reduce or prevent known workplace hazards (e.g., exposure to lead) and to monitor identified health problems. This can include preemployment baseline screening, periodic monitoring of exposure to potentially hazardous workplace substances, and drug screening. Skill is required in drawing blood samples, performing breathing tests, monitoring and documenting chain of custody, and obtaining properly signed and witnessed consent forms for drug, genetic, and HIV testing.


  • Nursing homes and long-term care facilities tend to produce more routine pretest, posttest, and follow-up testing because patients are frequently taken or transferred to hospitals for more complex procedures (e.g., computed tomography [CT] scans, endoscopies). Increasing numbers of full code (i.e., resuscitation) orders lead to greater numbers and varieties of tests. In addition, confused, combative, or uncooperative behaviors are seen more frequently in these settings. Understanding patient behaviors and using appropriate communication strategies and interventions for this patient population are necessary skills.


  • In the realm of public health, diagnostic test responsibilities focus on wellness screenings, preventive services, disease control, counseling, and treatment of individuals with problems. Case finding frequently occurs at health fairs, outreach centers, homeless shelters, municipal health departments, mobile health vans, and church settings. Responsibilities vary according to setting and may include providing test information, procuring specimens, and recommending referrals to appropriate caregivers. These responsibilities may even extend to transporting and preparing specimens for analysis or actually performing specimen analysis (e.g., stool tests for occult blood, tuberculosis (TB) skin testing, and procuring blood or saliva samples for HIV/AIDS testing).

The type of setting may also be determined by the type of test. Certain tests (e.g., cholesterol screening, blood glucose, electrocardiogram [ECG], lipid profiles, TB skin tests) can be done in the field, meaning that the service is brought to the patient’s environment. Other tests (e.g., x-rays using contrast media and those that require special patient preparation, invasive procedures, nuclear medicine procedures, hormone levels, and 24-hour urine testing panels) must be done in a healthcare setting. Magnetic resonance imaging (MRI) and ultrasound procedures are commonly performed in freestanding or specialty diagnostic centers. Complex tests such as endoscopic retrograde cholangiopancreatography (ERCP), cardiac catheterization, and bronchoscopy may require hospital admission or at minimum outpatient status. As testing equipment becomes more technologically sophisticated and risks associated with testing are reduced, the environment in which diagnostic procedures take place will also shift.

Although patient populations and testing environments vary, the potential contagions are universal and of concern for both the patient and the healthcare provider. Standard precautions must be used in all testing environments to ensure safety for patients and healthcare providers. Refer to Appendix A for an in-depth discussion of standard precautions.


Reimbursement for Diagnostic Services

Differences in both diagnostic care services and reimbursement may vary between private and government insurance. Nonetheless, quality of care should not be compromised in favor of cost reduction. Advocate for patients regarding insurance coverage for diagnostic services by informing the patient and his or her family or significant others that it may be necessary to check with their insurance company before laboratory and diagnostic testing to make certain that costs are covered. Coordinate with other healthcare team members, such as social workers and facility billing staff, for resources regarding insurance reimbursement.

Many insurance companies employ case managers to monitor costs, diagnostic tests ordered, and other care. As a result, the insurance company or third-party payer may reimburse only for certain tests or procedures or may not cover tests they consider to be not medically necessary. To help facilitate reimbursement for diagnostic services, be sure to include proper documentation (e.g., date of laboratory
service and specimen collected) and proper current procedural terminology (CPT) codes. Chart 1.2 lists laboratory tests that are covered by most insurance carriers, both private and government, which should be taken into consideration by the healthcare provider when selecting an appropriate test.








CHART 1.2 Tests Covered by Most Insurance Carriers

















































α-Fetoprotein


Blood counts


Blood glucose testing


Carcinoembryonic antigen


Collagen crosslinks, any method (urine osteoporosis)


Digoxin therapeutic drug assay


Fecal occult blood


γ-Glutamyltransferase


Glycated hemoglobin/glycated protein


Hepatitis panel


HIV testing (diagnosis)


HIV testing (prognosis including monitoring)


Human chorionic gonadotropin


Lipids


Partial thromboplastin time


Prostate-specific antigen


Prothrombin time


Serum iron studies


Thyroid testing


Tumor antigen by immunoassay—CA125


Tumor antigen by immunoassay—CA15-3/CA27


Tumor antigen by immunoassay—CA19-9


Urine culture



THE HEALTHCARE PROVIDER’S ROLE IN LABORATORY AND DIAGNOSTIC TESTING

Understanding the basics of safe, effective, and informed care is important. These basics include assessing risk factors and modifying care accordingly, using a collaborative approach, following proper guidelines for procedures and specimen collection, and delivering appropriate care throughout the process. Providing reassurance and support to the patient and his or her significant others, intervening appropriately, and clearly documenting patient teaching, observations, and outcomes during the entire process are necessary (refer to Fig. 1.1).


Preparing patients for diagnostic or therapeutic procedures, collecting specimens, carrying out and assisting with procedures, and providing follow-up care have long been requisite activities of professional practice. If test results are inconclusive or negative and no definitive medical diagnosis can be established,
other tests and procedures may be ordered. Thus, testing can become an involved and lengthy process. This care may continue even after the patient’s death. Diagnostic postmortem services include death reporting, possible postmortem investigations, and sensitive communication with grieving families and significant others regarding autopsies, unexplained death, other postmortem testing, and organ donation.

Healthcare providers need to work as a team to meet diverse patient needs, to facilitate certain decisions, to develop comprehensive plans of care, and to help patients modify their daily activities to meet test requirements in all three phases.

Insurance reimbursement for testing also influences trends. Managed care and case management, together with collaboration among the diverse healthcare disciplines and the patient, are key factors in determining how and to what degree optimal diagnostic services are used.

As societies become more culturally blended, the need to appreciate and work within the realm of cultural diversity becomes imperative. Interacting with patients and directing them through diagnostic testing can present certain challenges if one is not familiar with and sensitive to the healthcare belief system of the patient and his or her significant others. When facing language differences, it may be necessary for a translator to be present during all phases of the process to ensure clear communication. Special attention and communication skills are necessary for these situations as well as when caring for children and for comatose, confused, or frail patients. Consideration of these issues will significantly influence compliance, outcomes, and positive responses to the procedure. To be most effective, healthcare providers must be open to a holistic perspective and attitude that affects their caregiving, communication, and patient-empowering behaviors. Healthcare providers who understand the patient’s basic needs and expectations and strive to accommodate those as much as possible are truly acting as patient advocates.


ELEMENTS OF SAFE, EFFECTIVE, INFORMED CARE THROUGHOUT THE TESTING PROCESS

There are several key elements that must be considered and applied in order to ensure safe, effective informed care throughout the pretest, intratest, and posttest phases.


Communication

At the heart of informed patient-centered care is the ability to communicate effectively. Frequently, communication must take place within a compressed time frame because of time constraints. Thus, the importance of communicating effectively cannot be emphasized enough. Effective communication is the key to achieving desired outcomes, preventing misunderstanding and errors, and helping patients feel that they are secure, informed partners and are connected to the diagnostic process. One must always keep in mind that the human person is an integration of body, mind, and spirit and that these three entities are intimately bound together to make each person unique. Skillful assessment of physical, emotional, psychosocial, and spiritual dimensions provides a sound database from which to plan communication and teaching or instruction strategies.

Individuals have different needs and changing capacities for learning as they progress from child to adult to older adult. It is important for the healthcare provider to know the different developmental levels and stages and the ways in which clear communication can be achieved at any level.

For the pediatric patient, teaching tools might include tours of the diagnostic area, play therapy, films or videos, models of equipment that the child can touch or manipulate, and written materials and pictures appropriate to the child’s developmental stage. Shorter attention spans and the unpredictable nature of children can make teaching a challenge in this population. Mentally retarded or mentally ill patients may need significant others close by who can guide communication between caregiver and patient. Gentle, simple, nurturing behaviors usually work well with children and developmentally challenged individuals.


Adolescents may be at the stage of developing their own unique identity as they move toward adulthood. Teaching may be more effective without parents present; however, it is important to include parents at some point. Drawings, illustrations, or videos are helpful. Because body image is very important at this stage, honest, supportive behaviors are necessary, especially if some alteration in physical appearance will be necessary (e.g., removal of jewelry, no makeup allowed).

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Sep 25, 2018 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Diagnostic Testing
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