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CDC Addresses False Positive Results of Oral Fluid Rapid HIV Antibody Tests
Sexually transmitted disease (STD) clinics using the oral fluid rapid HIV antibody test have reported episodic increases in false positive results over the past few years. The New York City Department of Health and Mental Hygiene (NYC DOHMH) reported on these outcomes in the June 18, 2008 early release edition of Morbidity and Mortality Weekly Report (MMWR), published by the Centers for Disease Control and Prevention (CDC). The oral test, OraQuick Advance Rapid HIV-1/2 Antibody Test (Orasure Technologies, Bethlehem, PA), is performed using a sample of fluid taken from the mucous membranes of the mouth, eliminating the need for needles. These reports led NYC DOHMH to opt to instead use the older finger-stick rapid HIV blood test while efforts are underway to find the cause of the increase in false positive results for the oral test. The MMWR article covers testing done in New York City STD from March 2005 through May 2008. The first cluster of false positive oral fluid rapid test results occurred in late 2005 and subsided after several months. Another, larger increase in the incidence of false positive results began in late 2007 and continued through April 2008, at which time the NYC DOHMH discontinued offering the oral test at its STD clinics. From November 2007 through April 2008, the number of false positive test results exceeded the number that would have been expected based on the upper limit of the manufacturer's claimed accuracy. May data, which became available after discontinuation of oral fluid testing in the STD clinics, showed that the recent increase in false positive results had again subsided. From March 2005 through May 2008, the NYC DOHMH administered 160,174 oral fluid rapid tests, of which 0.27% returned confirmed false positive results. Thus, the oral fluid rapid test performed well overall, and within the manufacturer's limits described in the package insert. It should also be noted that during all months described in this report, the test operated within Food and Drug Administration (FDA) specifications, which call for a minimum threshold of 98.0% specificity -- that is, the probability that the test will be negative among patients who do not have HIV infection.
Role of Oral Fluid HIV Testing Oral fluid tests play an important role in HIV prevention efforts, making HIV testing possible in many venues where performing phlebotomy or finger-stick blood tests is impractical. The CDC continues to support the use of rapid oral fluid HIV tests. However, in general, FDA-approved testing with blood or serum specimens is more accurate than testing with oral fluid. In settings where blood specimens are already routinely obtained, blood or serum testing is preferred. The New York City experience demonstrates that repeating the same rapid test on finger-stick blood samples after a positive oral fluid test result can reduce the number of false positive results while minimizing the number of finger-stick tests that must be performed. Even when a follow-up rapid test is performed after a reactive oral fluid test, confirmatory testing (e.g., Western blot) is still required. CDC HIV testing guidelines recommend that a positive HIV test should be followed by a confirmatory test, regardless of the source of the initial test. The CDC has stated that it will continue to work with the NYC DOHMH, FDA, the test manufacturer, and other health departments and community-based organizations that provide HIV testing to establish the cause of the false positive results and to provide guidance to ensure that clients receive accurate HIV test results. Additionally, the CDC encourages all programs that administer rapid HIV tests to monitor confirmatory test results after reactive rapid tests. The agency also recommends that all providers clearly note the strengths and weaknesses of any HIV test, including the need to confirm reactive rapid tests. More information is available at the following links:
6/24/08 Reference
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