Acquired immunodeficiency syndrome (AIDS) is the final stage of infection caused by human immunodeficiency virus (HIV). The diagnosis of HIV involves an initial screening test followed by a confirmatory test. Most HIV diagnosis methods look for anti-HIV antibodies in the blood and are performed after the "window period," which is a period of 3 to 5 weeks after the initial exposure, when the anti-HIV antibodies are still being formed in the blood.
Rapid Tests
The rapid tests detect the presence of antibodies in blood or oral fluids and can provide results in as little as 20 minutes. Four rapid tests are available in the United States, and according to a 2006 review published in Current Infectious Diseases Reports, rapid tests play an important role in HIV prevention because they can provide early diagnosis and "expand access to testing in both clinical and nonclinical settings."
The rapid tests are highly sensitive and can detect the presence of small amounts of anti-HIV antibodies. However, these tests are less specific and can lead to false-positive reactions and hence should always be validated by confirmatory tests.
Enzyme-Linked Immunosorbent Assay (ELISA)
ELISA is the most common laboratory test used to look for anti-HIV antibodies in the blood and is effective when used after the window period. ELISA is an inexpensive test, and the results are available in 3.5 to 4 hours. However, many test centers send patients' samples to other laboratories, so it may take 1 to 2 weeks for the results to be available. As with the rapid tests, a positive ELISA test result should be confirmed with confirmatory tests. A negative ELISA test result may indicate lack of infection or early stages of infection and should be repeated after a few weeks.
Western Blot
Western blot is a confirmatory test that identifies the anti-HIV antibodies based on their molecular weight. This test is less sensitive and requires high levels of antibodies in the blood for results. However, it is highly specific for anti-HIV antibodies, and the chances of a false-positive reaction are very low. This test is only performed only when a rapid test or ELISA result is positive, and according to the information published on the San Francisco AIDS Foundation website, the results of a Western blot test may be positive, negative or indeterminate. An indeterminate result usually means that the anti-HIV antibodies have just begun form at the time of their test; in these cases, the person is retested after a month.
Immunoflurescent Assay (IFA)
IFA involves mixing of HIV antigen with a fluorescent compound and a sample of the patient's blood. If the patient's blood sample is positive, the mixture will radiate under ultraviolet light. IFA is not commonly available but is as reliable HIV confirmatory test, especially if performed 3 to 5 weeks after the exposure. In fact, the Food and Drug Administration (FDA) recommends this test to resolve indeterminate Western blot results.
Home-Based HIV Tests
Only one home-based test for HIV has been approved by the FDA, and AIDS.gov informs that test kit is not a true testing kit but instead a sample collection kit that includes the materials and the instructions for collecting a blood sample. The sample is then sent to a laboratory, where the traditional ELISA and Western blot tests are performed. This test is as reliable as any other test when all the instructions are followed and the test is performed after the window period.
