HIV and AIDS

HIV Test Sensitivity: False Negative and False Positive Results

HIV testing is done by two different types of tests: screening and confirmatory. These tests are meant to be very specific for HIV. Both tests should be positive before a result is called positive for HIV.

Screening test: The first test performed to determine for HIV status is called a "screening" test. The scientific name for this test is an ELISA. This test is purposely set to detect as many people as possible. If the ELISA test is positive, the lab usually repeats it on the same sample.
Confirmatory test: If the second test is positive, then they do a confirmatory test. This is scientifically called a western blot or immunofluoresence assay.

False positives

There is a small chance that one or either of these tests will be falsely positive. That is, the test is positive but the person really does not have HIV. Some diseases or vaccinations (Influenza shots) can occasionally turn the test positive but then on repeat it becomes negative.

An example of this is a patient I once had that received antibodies (immunoglobulins). They had a positive result that ultimately turned out negative once retested. The best advice is for anyone with a positive test to go see a doctor qualified to test and counsel them on HIV and be retested to confirm the results.

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Last Reviewed: Sep 05, 2008

Carl Fichtenbaum, MD
Associate Professor
Division of Infectious Diseases
Department of Internal Medicine
College of Medicine
University of Cincinnati