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Concept
Diagnosis of HIV/AIDS
Summary
HIV tests are used to detect the presence of the human immunodeficiency virus (HIV), the virus that causes acquired immunodeficiency syndrome (AIDS), in serum, saliva, or urine. Such tests may detect antibodies, antigens, or RNA.
AIDS-defining clinical condition
AIDS is diagnosed separately from HIV.
The window period is the time from infection until a test can detect any change. The average window period with HIV-1 antibody tests is 25 days for subtype B. Antigen testing cuts the window period to approximately 16 days and nucleic acid testing (NAT) further reduces this period to 12 days.
Performance of medical tests is often described in terms of:
Sensitivity: The percentage of the results that will be positive when HIV is present
Specificity: The percentage of the results that will be negative when HIV is not present.
All diagnostic tests have limitations, and sometimes their use may produce erroneous or questionable results.
False positive: The test incorrectly indicates that HIV is present in a non-infected person.
False negative: The test incorrectly indicates that HIV is absent in an infected person.
Nonspecific reactions, hypergammaglobulinemia, or the presence of antibodies directed to other infectious agents that may be antigenically similar to HIV can produce false positive results. Autoimmune diseases, such as systemic lupus erythematosus, have also rarely caused false positive results. Most false negative results are due to the window period.
Tests selected to screen donor blood and tissue must provide a high degree of confidence that HIV will be detected if present (that is, a high sensitivity is required). A combination of antibody, antigen and nucleic acid tests are used by blood banks in Western countries. The World Health Organization estimated that, , inadequate blood screening had resulted in 1 million new HIV infections worldwide.
In the US, the Food and Drug Administration requires that all donated blood be screened for several infectious diseases, including HIV-1 and HIV-2, using a combination of antibody testing (EIA) and more expeditious nucleic acid testing (NAT).
Official source
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