Choosing the Western Blot HIV Test
Individuals at risk for HIV infection should be tested on a regular basis. There are several types of HIV tests available, but the most common first test used is the enzyme-linked immunosorbent assay, or ELISA, HIV test. If the ELISA is negative, there is usually no need to continue testing. However, the ELISA test can sometimes be positive when the person is not infected with HIV, a result called a false positive. For this reason, a second test, such as the Western Blot HIV test, is used to confirm the infection. Both the ELISA and Western Blot tests detect the presence of antibodies that react with HIV proteins.
Performing the Test
Both the ELISA and Western Blot HIV tests look for the signs of an immune response to HIV, which indicates a person is infected. Plasma, a component of the blood, is incubated with a membrane that is embedded with HIV proteins. If the individual is infected with HIV, the person's plasma will contain antibodies that bind to HIV proteins. Laboratory technicians use sophisticated techniques to detect if antibodies have bound to the membrane. If antibodies are detected to multiple proteins, the result is usually considered positive. If no antibodies are detected, the result is negative.
Intepreting the Results
Unfortunately, interpretations of Western Blot HIV tests are not standard. However, this test is used as a secondary test to confirm the presence of HIV infection, which leaves more room for variation in interpretation. Typically the presence of antibodies that bind to two to three HIV proteins is considered positive.
A negative result indicates antibodies to HIV were not detected in the patient's blood. In the earliest stages of infection it is possible to test negative for HIV, because the body has not yet produced sufficient amounts of antibodies against the virus. For this reason, individuals at risk of contracting HIV should be tested regularly. If a physician suspects the patient is in the early phase of infection, she may order more sensitive tests to determine if HIV is present.
A positive result means the individual is infected with HIV. Sometimes, individuals who test positive with the ELISA test will receive a negative Western Blot result. This is especially true in people with certain medical conditions, such as lupus, Lyme disease and syphilis, which can lead to false positives by the ELISA method of testing.
Recommending Additional HIV Testing
Some patients may receive an indeterminate result by the Western Blot HIV test. This means the result appeared weakly positive, but it was not possible to definitively conclude the patient is infected. This occurs when antibodies bind to only one or two HIV proteins. In these cases, it is recommended to repeat HIV testing in one month, a sufficient window when most HIV-individuals will develop a positive result. If a positive result is not obtained within six months, the person is not infected with HIV. It is possible to have antibodies that bind to HIV proteins without being infected.
