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What Is an HIV Antibody Test?
When HIV enters the body, it begins to attack certain white blood cells called T4 lymphocyte cells (helper cells). Your doctor also may call them CD4 cells. The immune system then produces antibodies to fight off the infection. Although these antibodies are ineffective in destroying HIV, their presence is used to confirm HIV infection. Therefore, the presence of antibodies to HIV result from HIV infection. HIV tests look for the presence of HIV antibodies; they do not test for the virus itself.
What Blood Tests Detect the Presence of HIV?
HIV testing consists of an initial screening with two types of tests commonly used to detect HIV infection. The most commonly used initial test is an enzyme immune assay (EIA) or the enzyme-linked immunosorbent assay (ELISA). If EIA test results show a reaction, the test is repeated on the same blood sample. If the sample is repeatedly the same result or either duplicate test is reactive, the results are "confirmed" using a second test such as the Western blot. This more specific (and more expensive) test can tell the difference between HIV antibodies and other antibodies that can react to the EIA and cause false positive results. False positive EIA results are uncommon, but can occur. A person is considered infected following a repeatedly reactive result from the EIA, confirmed by the Western blot test.
In addition to the EIA or ELISA and Western blot, other tests now available include:
· Dot-blot immunobinding assay. A rapid-screening blood test that is cost-effective and that may become an alternative to standard EIA and Western blot testing.
· Immunoflourescence assay. A less commonly used confirmatory blood test used on reactive ELISA samples or when Western blot test results are uncertain.
· Nucleic acid testing (e.g., viral RNA or proviral DNA amplification method). A less available blood test that can be used to resolve an initial indeterminate Western blot result in certain situations.
· Polymerase chain reaction (PCR). A specialized blood test that looks for HIV genetic information. Although expensive and labor-intensive, the test can detect the virus even in someone only recently infected.
Do All HIV Tests Involve Drawing Blood?
No. Urine and oral-fluid HIV tests offer alternatives for anyone reluctant to have blood drawn.
Urine testing for HIV antibodies is not as sensitive or specific as blood testing. Available urine tests include an EIA and a Western blot test that can confirm EIA results. A physician must order these tests, and the results are reported to the ordering physician or his or her assistant.
Orasure© and OraQuick Advance HIV1/2 are currently the only FDA-approved oral-fluid tests. Fluid is collected from inside the mouth and analyzed using an EIA test and supplemental Western blot test, if necessary. Oral fluid tests are offered at many HIV testing locations. Contact a location near you to find out if this test is available.
What Are Rapid HIV Tests?
A rapid HIV test is a test that usually produces results in up to 20 minutes. In comparison, results from the commonly used HIV-antibody screening test, the EIA, are not available for 1-2 weeks.
There are currently four rapid HIV tests licensed for use in the United States:
· OraQuick Rapid HIV-1 and Advance HIV ? Antibody Tests, manufactured by OraSure Technologies Inc.
· Reveal G2 HIV-Antibody Tests, manufactured by MedMira Inc.
· Multispot, manufactured by Bio-Rad Laboratories
· Uni-Gold Recombigen, manufactured by Trinity Biotech
The availability of these tests may differ from one place to another. These rapid HIV blood tests are considered to be just as accurate as the EIA. As is true for all screening tests (including the EIA), a positive test result must be confirmed with an additional specific test before a diagnosis of infection can be given.
What About Home Test Kits?
The U.S. Food and Drug Administration has not approved home-use HIV test kits, which allow consumers to interpret their own HIV test results in a few minutes. The Federal Trade Commission has warned that these home-use HIV test kits, many of which are available on the Internet, supply inaccurate results.
Currently only the Home Access test is approved by the FDA. The Home Access test kit can be found at most drug stores. The testing procedure involves pricking your finger, placing drops of blood on a specially treated card, and then mailing the card in for testing at a licensed laboratory. Customers are given an identification number to use when phoning for the test results. Callers may speak to a counselor before taking the test, while waiting for the test result, and when getting the result.