This is the most commonly used blood test today. ELISA stands for enzyme-linked immunoabsorbant assay. It is very sensitive in detecting specific types of antibodies as well as small numbers of antibodies. Unfortunately, because it is so sensitive it may return a false positive due to other proteins and antibodies. Specifically, one study found that 84% of positive results from three ELISA tests were truly negative!(4) This is why mandatory testing has never been ordained in the United States. People infected with malaria may also return a false-positive result from the ELISA test, which is a major problem in Africa where malaria is rampant.
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The way the ELISA test works is very simple. A large amount of HIV-1 (the most common form) is prepared and antigens (substances that elicit an immune system response) are isolated from it. The test antigens are put into individual cells. The patient's blood serum is then added to a well. It is left alone for an hour to allow any antibodies to bind to the HIV. The blood serum is cleared away and the remaining substance is treated with a chemical, which produces a certain color if antibodies are attached to the antigens.
In this picture, a positive reading from the ELISA test is determined by the amount of yellow color in each cell.
Usually a positive result from ELISA is checked using the more tedious and expensive Western Blot test.
- “AIDS.” Encyclopedia Britannica. 2004. Encyclopedia Britannica Online. 4 Jan. 2004. <http://search.eb.com/eb/article?Eu=4225>.
- Check, William A. AIDS . New York: Chelsea House Publishers, 1988. The Encyclopedia of Health.
- Silverstein, Alvin. AIDS: An All-About Guide for Young Adults . Springfield: Enslow Publishers, 1999.
- Storad, Conrad J. Inside AIDS: HIV Attacks the Immune System . Minneapolis: Lerner Publications Company, 1998.
- Wright, Michael P. Thousands of HIV False Positives in the U.S. 10 Feb. 2004. <http://www.sumeria.net/aids/false.html>.
