HIV

To understand what your test results mean, you first have to understand what kind of test is being used and what a "window period" is.

Most HIV screening tests look for HIV antigen (part of the HIV virus) or for HIV antibodies (produced by the person's body), or may look for both. Newer testing strategies use a combination antigen/antibody test. Some testing sites also use a test that looks for genetic material of the HIV virus.

The window period is the period between the time someone is first infected with the HIV virus and the time an HIV test can detect HIV infection. After someone has been infected with the virus it can take about 2 weeks for HIV antigen to be detectable with current antigen tests, and more than 3 weeks to produce enough HIV antibodies to be detected by antibody tests. In a very small number of people, the process takes up to several months.

During the window period, someone might be infected with HIV yet still have a negative result on an HIV test. Here's how that can happen. Let's say you have condomless sex on Saturday night and become infected with HIV. On Monday, you get an HIV test. The test almost certainly will come back negative, because there is not yet enough HIV antigen or HIV antibody for the tests to detect.

Even if you go for an HIV test 2 or 3 weeks later, an antibody test result might be negative because your body still has not produced antibodies (an antigen test may be positive at an earlier time point). If you think you have been exposed to HIV, and your test results are negative, be sure to discuss this with your medical providers--they may want to test you directly for HIV virus (an HIV viral load) or repeat a sensitive HIV antigen/antibody test.

Newer methods of HIV testing are narrowing the time of the "window period" and reducing the chance of a falsely negative result.

When testing is completed, your provider will tell you the result. Possible results are:

Positive: means that you have HIV infection. Your provider will discuss treatment and refer you to a specialist for HIV care.

Negative: means either you do not have HIV or you got it so recently that your body has not had time to make enough antibodies to be detected by the test. If your result is negative but other things seem to point to HIV as a possibility, you should have the test repeated later.

Indeterminate: means that the test did not show whether or not you have HIV. This could happen if you have another medical condition that interfered with the test or you have been infected recently. If you have an indeterminate HIV test result, you need to have an HIV test repeated at a later date.