June 2008

CDC.gov: Issues with Oral Fluid Rapid Tests

The New York City Department of Health and Mental Hygiene (NYC DOHMH) reports in the June 18, 2008 Morbidity and Mortality Weekly Report (MMWR) (early release) article “False-Positive Oral Fluid Rapid Tests, New York City 2005-2008” that sexually transmitted disease (STD) clinics in NYC using the oral fluid rapid test have reported episodic increases in false-positive tests over the past few years. These reports have resulted in NYC DOHMH opting to use the finger stick rapid test while efforts are continuing to find the cause of the increase in false-positive results. The test, OraQuick Advance Rapid HIV-1/2 Antibody Test (Orasure Technologies, Bethlehem, PA), can be performed on oral fluid and has broadened the settings in which HIV testing can be provided. The MMWR article covers testing done in STD clinics in New York City from March 2005 through May 2008.

The first cluster of false-positive tests occurred in late 2005 and subsided after several months. Another, larger increase in the incidence of false-positive oral fluid rapid test results began in late 2007 and continued through April 2008, at which time the NYC DOHMH discontinued offering this test in its STD clinics. From November 2007 to 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 claim. (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 subsided). From March 2005 through May 2008, the NYC DOHMH administered 160,174 oral fluid rapid tests, of which 0.27% of the tests were confirmed false-positive results. Thus, overall the oral fluid rapid test performed well 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 the Food and Drug Administration (FDA) regulations, 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 the infection.

Oral fluid tests play an important role in HIV prevention efforts, making HIV testing possible in many venues where performing phlebotomy or fingerstick is impractical. 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 obtained routinely, testing with blood or serum specimens is preferred. NYC’s experience demonstrates that repeating the same rapid test on fingerstick whole blood after a reactive oral fluid test result can reduce the number of false-positive test results while minimizing the number of fingerstick tests that must be performed. Even when a follow-up rapid test is performed after a reactive oral fluid test, confirmatory testing is still required.

CDC will continue to work with the NYC DOHMH, FDA, 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 patients receive accurate results from their HIV tests. Additionally, CDC encourages all programs that administer rapid tests to monitor confirmatory test results after reactive rapid tests. Further, CDC recommends that all providers clearly note the strengths and weaknesses of any HIV test, including the need to confirm reactive rapid tests, when offering one to a patient.

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.