Human immunodeficiency virus (HIV) is diagnosed through a blood test that reveals the presence of antibodies to the virus in the bloodstream. Generally, it takes between six and 12 weeks following infection before these antibodies develop. In rare cases, it can take up to six months before these antibodies show up in blood tests.

For years, the enzyme-linked immunosorbent assay (ELISA) was the standard blood test used to detect HIV. Patients who tested positive would receive a second ELISA test to ensure that the positive reading was accurate. If this test also came back positive, the patient would be given a Western blot test to check for the presence of HIV proteins. The blot test was used to ensure that non-HIV antibodies were not causing a false-positive reading.

However, this testing took up to two weeks before results were ready. As a result, tests were developed that provide results in as little as 20 minutes. Both of these types of tests look for HIV antibodies, one through a finger prick of blood and the other through analysis of secretions collected by a pad from the mouth. If either of these tests produces a positive result, a blood test will be needed to confirm the diagnosis.

At present, the Food and Drug Administration (FDA) has approved just one test available for home use. The Home Access HIV test (marketed by Home Access Health) allows a patient to mail in a drop of blood before calling a toll-free number to receive the results in three to seven business days. The test is considered to be as accurate as a clinical test. Patients are identified by a code number that comes with the kit to ensure privacy. If the test comes back positive, the patient is referred to medical or social services.

Patients who test positive will have their blood checked for the amount of virus in the bloodstream, which is known as viral load. This can help a physician to predict the probable progression of the disease and to formulate the appropriate treatment plan.

Sexual partners should be notified of the diagnosis so they may seek medical testing and treatment. Intravenous drug users should also notify anyone with whom they may have shared a needle with. Some health clinics provide anonymous partner notification systems, which notify people that they may have been exposed to HIV, without informing them of who reported their names or when the exposure occurred.