Important note: Information in this article was accurate in 1988. The state of the art may have changed since the publication date.
Food and Drug Administration, U.S. Department of Health and Human Services - December 13, 1988
Brad Stone - (301) 443-3285
Useful when a quick screening result is required, the new test also is designed to be used by trained health professionals in settings in which other types of AIDS antibody detection tests cannot be performed because of the lack of refrigeration and sophisticated equipment.
FDA Commissioner Frank E. Young, M.D., Ph.D., said that the test is the first for AIDS virus infection to be developed by gene-splicing techniques. "This technical advance," Dr. Young said, "should help make testing available to all who want to be tested. It will also be particularly useful in remote areas of the world that lack the facilities for earlier approved tests and may also be very useful as a preliminary screening measure in emergency situations in this country.
"It is not, however, intended to replace the current tests used by blood banks for screening donated blood. Furthermore, any positive reactions using this screening test must be confirmed because false-positive reactions can occur."
Called a latex agglutination test kit, the new test is a suspension of microscopic latex beads coated with a genetically engineered protein which contains portions of the outer surface, or envelope, of the AIDS virus. The engineered protein is produced by a process in which a part of the AIDS virus genetic material is inserted into E. coli bacteria. As the bacteria grow, a large amount of the modified AIDS virus envelope protein is produced. The engineered virus protein is purified further before it is coated onto the latex beads.
This production process is much safer than previous methods relying on growing live AIDS viruses in a cell culture.
When a sample of whole blood, plasma or serum is mixed with the protein-coated latex beads, AIDS antibodies, if present in the sample, will bind to the beads causing them to clump, or agglutinate. A trained professional can visually detect this clumping reaction with a bright light.
The agglutination test supplements the series of other approved AIDS antibody test kits that have been used to screen the blood supply. The screening test which is recommended for routine use in blood banks and clinical laboratories, the enzyme-linked immunosorbent assay, or ELISA, was first licensed by FDA in March 1985.
Another, more specific test known as the Western blot was approved in April 1987. The universal use of these two types of blood screening kits by blood establishments within the United States -- along with voluntary self-exclusion by high risk groups -- has effectively safeguarded the nation's blood supply from contamination with the AIDS virus.
When properly performed by trained medical professionals, the latex agglutination test can provide a highly sensitive assay for AIDS virus antibodies within five minutes, compared to the several hours it takes to develop results using the other test kits. The new test kit is not well adapted, however, for screening very large numbers of samples. Also, false-positive reactions can occur because of interpretation errors, some medical conditions and problems of sample quality that do not ordinarily affect the ELISA test. As with other screening tests, positive test results should be further investigated by repeat testing, including a test with a fresh sample, and by validation with additional, more specific tests based on independent methods such as the Western blot.
The approved test kit will be manufactured by Cambridge Bioscience Corp. of Worcester, Mass., and distributed by Baxter Health Care Corp. under the trade name Recombigen HIV-1 Latex Agglutination Test.
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SOURCE: Food and Drug Administration (FDA).
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