Types of HIV Tests
A number of tests are done to come to or confirm a diagnosis of HIV infection. Still other tests are done to monitor the progress of HIV disease. These tests use various techniques and screen for a range of different factors (i.e., antibodies to HIV, viral genetic material, number of copies of the virus, number of certain types of lymphocytes). Testing is the only way to know one's HIV status and to monitor progress of HIV disease before symptoms occur.
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Antibody Tests
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Most initial HIV tests screen for the presence of antibodies to the virus; these tests are called ELISA (enzyme-linked immunosorbent assay). Because these tests rely on antibodies to diagnose, seroconversion must have already taken place in order for these tests to be accurate. Seroconversion is the process of developing a detectable level of antibodies.
These tests can be conducted with samples of blood taken via a needle, from a swab of oral secretions or from a urine sample; however, urine testing is somewhat less accurate, according to HIVTest.org.
There are also rapid HIV tests, which can yield an accurate result within 20 minutes, as well as one approved home test for HIV: the Home Access HIV-1 Test System. No other home test has been approved by the Food and Drug Administration, and no other home test should be used.
RNA Tests
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Some initial HIV tests screen for the virus RNA by using a process called polymerase chain reaction, in which viral genetic material is amplified so that it can be detected. The advantage of these tests is that they can detect HIV earlier in infection; however, they are at present not as widely available as more standard tests.
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Confirmatory Testing
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When an initial HIV test yields a positive result, it must be confirmed by another test. The confirmatory test most commonly used is the Western blot; according to HIV InSite, this test better distinguishes between HIV antibodies and other antibodies but may not always produce a clear result. Another test, the indirect fluorescent antibody test, is less commonly used because it is more expensive.
Viral Load Testing
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Viral-load testing, which detects the number of copies of the virus in the system, is used to monitor the progression of HIV-disease as well as to gauge the effectiveness of a current course of treatment in an individual. Viral-load testing is also used to screen newborns for HIV, according to HIV InSite, because antibody tests would not yield an accurate result at that time.
CD4 Cell Count
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HIV targets a particular lymphocyte (immune cell) called the CD4 T-cell. HIV infects these cells and integrates itself into them, as a result of which these cells begin to make copies of HIV instead of participating in the body's immune response. CD4 testing is used as a diagnostic tool for AIDS (a CD4 cell count of 200 or fewer per cubic milliliter of blood) or to determine when to begin treatment, which the U.S. Department of Health and Human Services recommends be started when the CD4 cell count is 350 or lower.
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