Understanding Your HIV Test Results

There are a number of different tests that can be used to diagnose HIV infection. The most commonly used tests are called "HIV antibody tests." Antibodies are the body's reaction to HIV.

Standard antibody HIV testing can have two stages. The most commonly used initial screening test is either an enzyme immune assay (EIA) or the enzyme-linked immunosorbent assay (ELISA). If the EIA/ELISA test is negative, no additional testing is done. If the EIA/ELISA screening test is positive, that result must be confirmed with a more specific test called "Western Blot."

Rapid HIV testing using oral fluids or blood specimens are EIA/ELISA screening tests that provide results in 20 minutes. This kind of test has been shown to be highly accurate (99.5%) and comparable to the blood tests that are performed in a lab. A positive result from a Rapid EIA test is considered "preliminarily positive" and must be confirmed with a Western Blot performed in a lab.

HIV Antibody Testing:

HIV antibody tests can have three different results: positive, negative or indeterminate (inconclusive).

• A positive result on a confirmed HIV antibody test means that HIV antibodies are present and you are infected w ith HIV (called "HIV positive"). To read about clinical trials for HIV-positive people, click here to learn about on-going studies at the NYU/Bellevue AIDS Clinical Trials Unit.
• A negative result on an HIV antibody test means that most likely you are not infected with HIV. However, it can take 3 to 6 weeks, and sometimes up to 3 months (and in few cases up to 6 months) before HIV antibodies show up on a standard test. As a result, some people who are recently infected with HIV may still have a negative test result during this time. This is called the "window period." The window period is why it is important to be tested for HIV regularly. If you are concerned about a possible recent exposure to HIV, you may be tested through First Call NYU.
• An indeterminate/inconclusive result means that the antibody test was neither positive nor negative. This may be a result of:
  • Recent HIV infection,
  • Prior blood transfusions, even with non-HIV infected blood,
  • Prior or current infection with syphilis, malaria, or other viruses,
  • An autoimmune disease such as lupus or diabetes,
  • Being a recipient of an experimental HIV vaccine,
  • Or problems with the test procedure itself, such as contamination of the blood sample.

If a person has an indeterminate HIV test result, the test should be repeated. If the test results continue to be indeterminate, there are other tests that may be done to detect an infection. First Call NYU offers enhanced HIV testing that can detect an infection even when a Western Blot is "indeterminate." If you have received an indeterminate result, please call (212) 263-3544 or email firstcallnyu@med.nyu.edu

Western Blot Tests Illustrate the Window Period

Below are some photographs of Western Blot tests. On the left side of the image there are two columns to be used as points of comparison. The column marked "NC" is an HIV-negative test result and the column marked "PC" is an HIV-positive test result. Columns 3 to 10 show a series of tests on an individual person who became infected with HIV to illustrate how an HIV test result can change during the window period from HIV-negative to HIV-positive. Each column is one Western Blot test. These tests were performed on a single person beginning with the day the person was first infected with HIV (Column 3, Day 0) to when the person had a conclusive HIV infection (Column 10, Day 30). Each black or dark grey horizontal stripe is representative of the presence of a different antibody against a protein found in HIV. To be conclusive (HIV-positive), a Western Blot must have 5 horizontal stripes. An HIV infection is not the same as an AIDS diagnosis.

PCR/Viral Load Testing:

A PCR (Polymerase Chain Reaction) test, also known as a "viral load," is used to measure the amount of HIV in an HIV-positive person's blood. Because this test looks for HIV directly in a person's blood instead of detecting antibodies (the body's reaction to HIV), it may detect an HIV infection about a week after an exposure. Therefore the PCR test is used by researchers and health care providers to identify infections during the window period.

An explanation of any term used in these descriptions can be found in the HIV/AIDS Dictionary.