Am I Infected? <BR>(A Guide to Testing for HIV) : What are the types of HIV tests?

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Am I Infected?
(A Guide to Testing for HIV)
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What are the types of HIV tests?

There are several different tests that can be used to determine if you have HIV. The first test developed is still the most frequently used for the initial detection of HIV infection: the enzyme-linked immunosorbent assay, or as it's more commonly known, the ELISA or EIA.

There are a variety of ELISA/EIA tests available. Some involve drawing blood from a vein. The sample is sent to a laboratory for analysis, with results available within one or two weeks.

Many testing sites are now using oral or finger prick rapid assays. The oral test, for example, involves swabbing the upper and lower gums inside the mouth. The sample is then placed into a developer vial, with results available within 20 to 40 minutes.

The Centers for Disease Control and Prevention (CDC) recently recommended a new HIV testing protocol for laboratories that will take advantage of advances in testing technology and will better identify acute, or very recent, cases of the virus. These new "fourth generation" HIV tests for both antibodies to the virus in blood samples and for what's known as the HIV-1 p-24 antigen, which shows up in the body sooner than antibodies.

The time it takes the body to produce antibodies after HIV infection has begun is known as the "window period." For the vast majority of those who contract the virus, antibodies to HIV will develop within four to six weeks after exposure. Some will take a little longer to develop antibodies. Until antibodies are present, an ELISA test will come up negative for HIV. So if someone has indeed contracted the virus but hasn't yet developed antibodies when taking an ELISA HIV test, this can result in a false negative.

The newer HIV tests will detect an infection by about three weeks following exposure to the virus; with the older HIV tests, the window period could be as long as three months. Correctly identifying acute cases of HIV is crucial for HIV prevention because viral loads are typically very high during that period of infection, making someone much more likely to pass on the virus.

Because of this window period, it is important to know what type of HIV test your health care provider is using. With the older tests, getting tested before three months may give you an unclear result or a false negative.

If the initial HIV test is positive, the next step is to perform an HIV-1/HIV-2 antibody differentiation immunoassay in order to determine if the individual is carrying HIV-1 or HIV-2. This test will produce results faster than the previously recommended Western Blot test.

If there is a negative or indeterminate result of the second testing step, then the CDC recommends a nucleic acid test. A negative result of that test indicates a false positive result on the earlier test, meaning that the individual does not have HIV. A positive result indicates an acute infection.

No diagnostic test will ever be 100 percent reliable, but if you test negative at the appropriate time (i.e., 3 weeks after possible exposure to the virus with the newer HIV tests or 13 weeks after possible exposure to the virus with the older HIV tests), you can consider that to be a dependable confirmation that you are HIV negative.

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Last Revised: November 17, 2014

This content is written by the POZ and AIDSmeds editorial team. For more information, please visit our "About Us" page.

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