The main tests used for detecting HIV infection are blood tests:
- Enzyme immunoassay (EIA) This test is widely used by just about all HIV testing programs. It is highly accurate but no test is 100 percent accurate. Accuracy depends on following proper procedures as well as the person's stage of infection. That is why all HIV testing programs use more than one test to confirm the presence of HIV.
- Enzyme-linked immunosorbent assay (ELISA)
- Western blot test, which is used to confirm the EIA/ELISA screening tests
In all of these tests, a small amount of blood is drawn from the arm and taken to the lab to be tested. The EIA and ELISA tests take from one to two weeks to complete, depending on where the test is performed. These tests check for the presence of antibodies to HIV; they do not check for the virus itself.
In addition to the standard blood tests for HIV, other tests are available:
A rapid test for detecting antibodies to HIV was first approved in the U.S. in 1996. This test produces very quick results, usually in 10 minutes, much faster that the standard HIV tests (EIA and ELISA) that are not available for one to two weeks. These rapid tests are increasingly being used because of the faster turnaround time.
The U.S. Food and Drug Administration currently has licensed only one rapid HIV test called the Single Use Diagnostic System for HIV-1 (SUDS™). Several others are in development. The availability of rapid HIV tests may differ from one place to another.
The rapid HIV test is an ELISA test. But instead of being analyzed in large batches along with other individual tests, the rapid test is analyzed alone. The slightly higher cost is outweighed by a fast result, which reduces the number of people who never return to find out their results.
If the result is negative a person can leave the testing site. However, if the rapid test is positive, other tests, including the Western blot, will be used to confirm the results before the person is told of the presence of HIV infection.
Consumer-controlled test kits (popularly known as "home test kits") were first licensed in 1997. Although home HIV tests are sometimes advertised through the Internet, currently only the Home Access Express HIV-1 Test System manufactured by Home Access Health Corporation is approved by the U.S. Food and Drug Administration (FDA). The accuracy of home test kits other than Home Access - many of which are available online - cannot be verified.
The approved Home Access test kit can be found at most local drug stores. The testing procedure involves pricking your finger with a special device, placing drops of blood on a specially treated card, then mailing the card in to be tested at a licensed laboratory. Customers are given an identification number to use when phoning for the test results. Callers may speak to a counselor before taking the test, while waiting for the test result, and after getting the result.
Oral tests can be performed in a doctor's office or clinic. To use an oral HIV test, the inside of the mouth is gently scraped and the saliva is tested for the presence of HIV antibodies. The result is as accurate as the blood tests because the saliva is tested using an EIA test and then a Western blot test if necessary.
It's important to remember that saliva is not a medium through which the HIV virus is transmitted. Semen, vaginal fluids, and blood are the main body fluids by which the HIV virus is transmitted.
A urine-based test is also available for screening in a doctor's office or clinic. However, it is somewhat less accurate than the blood or saliva-based tests. Like other tests, positive results must be confirmed with the Western blot test. A physician must order these tests, and the results are reported to the physician's office.
Other tests that measure HIV in the blood directly are available:
- A p24
antigentest measures a specific protein of the virus in the blood.
- An RNA viral load test measures the quantity of viral RNA in the blood. This test is often used to measure the effectiveness of drugs used to treat HIV infected people.
Need To Know:
Polymerase chain reaction (PCR) is a new blood test that looks for HIV genetic information. It has very limited availability. It is expensive and labor intensive but the advantage is that the test can detect the virus even in someone who is newly infected. The FDA has indicated that the development and implementation of tests for HIV genetic material such as PCR is warranted.