HIV test
HIV tests are used to detect the presence of the human immunodeficiency virus in serum, saliva, or urine. Such tests may detect HIV antibodies, antigens, or RNA.
Main article: AIDS
Terminology
The window period is the time from infection until a test can detect any change. The average window period with antibody tests is 22 days. Antigen testing cuts the window period to approximately 16 days and NAT (Nucleic Acid Testing) 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 results are when the test concludes HIV is present when, in fact, the person is not infected.
- False negative results are when the test concludes HIV is not present, when in fact the person is infected.
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, can also cause false positive results.
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