ELISA

From AIDS Wiki

ELISA (Enzyme Linked Immuno-Sorbent Assay), also sometimes known as EIA, is a form of test where multiple proteins (antigens) believed to be from HIV are mixed together with color-changing chemicals. When a sample that might contain antibodies to HIV is added a color change may occur. If the color produced is of a high enough intensity a reactive test result is declared.

In richer countries the ELISA is not trusted alone. Usually two or three positive ELISA tests are needed followed by a Western Blot test before the sample is declared to be HIV-positive. Technical problems with the ELISA test include cross-reactions with other viruses or conditions and reactions with components of the test kit. Logical problems are more significant and include the question of why antibodies are believed, in the case of HIV, to indicate current infection, and not just past exposure (as with most diseases). Furthermore, the test is totally reliant on the meaning of the antigens that it is created from. Given that HIV has never been purified, it is impossible to know whether the antigens in the test are really from HIV.

For a review of the science of HIV testing see the Rethinking AIDS testing web site.