I have had a terrible time since being diagnosed with a false-positive HIV test. I was stuck by a needle at work and was tested along with the patient. (I am a nurse.) His labs came back okay, but my HIV-1 antibody EIA came up positive. The Western Blot showed ABSENT. I had blood sent to another lab, and the results were nonreactive. The doctor felt that my false-positive result came from a flu vaccine I had taken. Do you agree that I am a false-positive? If so, will I always show positive?

Jo

You did not test positive for HIV, the virus that causes AIDS. The U.S. Centers for Disease Control (CDC) defines a positive test for HIV as "a repeatedly positive ELISA followed by a positive Western blot test," and you did not have either.

An EIA or ELISA test detects antibody against HIV. Antibodies are proteins our bodies produce that recognize "antigens" (parts of viruses or other foreign material). The ELISA test detects antibody against a single HIV antigen. The test can have false-positive results, and the influenza vaccine has been reported to sometimes cause them. One of the most common causes of a false-positive ELISA is laboratory error. Other causes include pregnancy, recent blood transfusion and autoimmune diseases such as lupus. As an example of how common false-positive results are, the Johns Hopkins hospital website reports that two percent of all ELISAs done at that institution are false-positive.

The Western blot test looks at several antigens on HIV. Two separate antigens have to be present for the test to be positive. These show up as "bands" on a gel. This test is much more specific for HIV than ELISA, meaning there are very, very few false-positive results on the Western blot test. In fact, the risk of a false-positive Western blot is estimated to be less than 1 in 250,000. Most cases occur in people who have received experimental HIV vaccines.

I have always had a policy of NEVER releasing a positive HIV test result to a patient until the Western blot was performed. The HIV test, in my mind, is not complete until all the results are in. This means two positive ELISAs and a positive Western blot test.

I do not know why you had a positive ELISA. It is possible it was simply a lab error. You state that you were retested in another lab and it was negative. This suggests that you do not have antibodies against HIV in your system. I doubt that you will ever test positive again by ELISA. But even if you do, I would still rest assured that you do not have HIV.

If you are at all concerned, I would simply be retested after six months or so. But this time, do not find out the result of the ELISA. Just ask your doctor if you are HIV-negative or not. That is all that matters.