HIV testing

A negative test result is normal. However, early HIV infection (termed acute HIV infection or primary HIV infection) often results in a negative test.

A positive result on the ELISA screening test does not necessarily mean that the person has HIV infection. There are certain conditions that may lead to a false positive result, such as Lyme disease, syphilis, and lupus.

A positive ELISA test is always followed by a Western blot test. A positive Western blot confirms an HIV infection. A negative Western blot test means the ELISA test was a false positive test. The Western blot test can also be “indeterminate,” in which case additional testing is done to clarify the situation.

Negative tests do not rule out HIV infection. There is a period of time (called the "window period") between HIV infection and the appearance of anti-HIV antibodies that can be measured.

If a person might have acute or primary HIV infection, and is in the "window period," a negative HIV ELISA and Western blot will not rule out HIV infection. More tests for HIV will need to be done.

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ELISA/Western blot tests for HIV Overview

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ELISA/Western blot tests for HIV Risks

Review Date: 06/05/2009
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; Jatin M. Vyas, MD, PhD, Assistant Professor in Medicine, Harvard Medical School, Assistant in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org)