HIV testing is done to determine whether or not someone is infected with the Human Immunodeficiency Virus (HIV), the virus which causes Acquired Immune Deficiency Syndrome (AIDS). Sexually active individuals, intravenous drug users, and health care workers should obtain HIV testing on a regular basis, ideally once a year. There are many different types of tests used to look for the presence of HIV in the body, and there are anonymous testing options for people who want to be tested, but are concerned about their privacy.
There are three basic kinds of HIV testing available: antibody tests, antigen tests, and polymerase chain reaction (PCR) tests. Antibody tests look for the presence of antibodies to HIV, indicating that the patient is infected. Antigen tests look for the antigens on the surface of the virus which lead to the development of antibodies, while PCR tests look for the actual RNA and DNA of the virus. Antibody tests are the ones in most common usage.
In HIV testing, a sample of the blood, urine, or oral mucus is taken and run through a series of tests in the lab. In the case of antibody testing, lab workers most commonly use an enzyme-linked immunosorbent assay (ELISA) test, which is around 95% accurate. The advantage of the ELISA is that it very rarely generates a false negative result. It can, however, generate a false positive, so if an ELISA indicates the presence of infection, the test needs to be confirmed by being repeated, or the sample can be run through a Western blot or indirect immunofluorescence assay to confirm the presence of HIV.
Patients do not start to make antibodies, known as seroconverting, until around two to eight weeks after exposure, and it can take as long as three months for antibodies to show up with HIV testing. For this reason, people should wait to be tested until at least eight weeks after a suspected exposure, and if the result is negative, they should repeat the test at three months. The period in which people are infected but antibodies are not yet present is known as the “window period,” and it is important to be aware that people in the window period could still have HIV, even if tests are negative.
There are tests which can be used during the window period to look for the virus. PCR tests, which search for the actual virus, are very expensive, but very accurate, and they may be used by people who want to use aggressive treatment to tackle the virus. Antigen tests can also be used during this period.
HIV testing can result in positive, negative, or inconclusive results. A positive result indicates that someone is infected with HIV, and that the test has been confirmed with a second method. Positive results do not mean that the patient has AIDS, or that he or she will necessarily develop AIDS, but they do mean that the patient needs special medical care, and is at risk of passing the virus on to others. Negative results show that someone is not infected, or has not seroconverted. Inconclusive results usually suggest that someone should be retested in several weeks, as the sample may have been contaminated, or the patient may have been seroconverting at the time the sample was taken.
Rapid tests can generate results in around 20 minutes. Other tests, including home collection kits, usually take several days or weeks to turn around, because they are processed at off-site labs. Some regions will accept rush orders for HIV testing, in which case a fee will be charged.