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Overview of False-Positive Oral Fluid Rapid HIV Tests

August 12, 2008

The New York City Department of Health and Mental Hygiene (NYC DOHMH) describes "False-Positive Oral Fluid Rapid Tests, New York City 2005-2008" in the Centers for Disease Prevention and Control's (CDC's) June 18, 2008 Morbidity and Mortality Weekly Report (MMWR) (early release). The MMWR report covers oral fluid rapid HIV testing done in sexually transmitted disease (STD) clinics in New York City (NYC) from March 2005 through May 2008. STD clinics in NYC using the oral fluid rapid test reported two episodic increases in false positive test results over the past four years. Because of the second episode of increases in false-positives since November 2007, the NYC DOHMH decided to suspend oral fluid testing and use the finger-stick whole blood specimens instead, which have not shown an increase in false-positive results.

The test, OraQuick Advance Rapid HIV-1/2 Antibody Test (Orasure Technologies, Bethlehem, PA), can be performed on blood or oral fluid and has made HIV testing possible in many more settings than before.

From March 2005 through May 2008, the NYC DOHMH administered 166,058 oral fluid rapid tests, with 442 (0.27%) false-positive test results. Overall, despite the increases in false positive results, the oral fluid rapid test performed well and above the Food and Drug Administration's minimum threshold of 98.0% specificity.

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The first cluster of false positive oral fluid test results that occurred in 2005 continued for several months. Another, larger increase in the number of false-positive test results began in late 2007 and continued through April 2008. The NYC DOHMH discontinued offering the oral fluid test in its STD clinics after May 27, 2008. (May data, which became available after discontinuation of oral fluid testing in the STD clinics, showed a much lower number of false-positive oral fluid test results than in preceding months.).

After the first increase in false-positive test results in late 2005, the NYC DOHMH STD clinics began offering an immediate finger-stick rapid blood test to patients who had a preliminary positive result using the oral fluid rapid test. Following the oral fluid rapid HIV test with a rapid test on finger-stick whole blood provided counselors with better information so they could provide clients with a more accurate interpretation of their initial test results. In addition, using the a finger-stick whole blood rapid test after a reactive oral fluid rapid HIV test allowed the NYC DOHMH to minimize the number of finger-stick tests that were performed. It is important to note that confirmatory testing was still conducted by NYC DOHMH as it is required after any reactive rapid test.

CDC continues to support the use of the rapid oral fluid HIV test. This test plays an important role in HIV prevention efforts, making HIV testing possible in many venues outside of clinical settings, and increasing the opportunities for persons to learn their HIV status. A reactive oral fluid test however, is preliminary and does require confirmatory testing.

CDC will continue to work with the NYC DOHMH, FDA, the test manufacturer, and with other health departments and community-based organizations that provide HIV testing to establish the cause of the increases in false-positive test results and to provide guidance to those administering testing to help ensure patients receive an accurate HIV test result. In general, HIV testing with blood or serum is more accurate1 and the preferred method in clinics or other facilities where blood specimens are already obtained routinely. CDC encourages all programs that administer rapid tests to monitor the confirmatory test results after reactive rapid tests and keep track of the number of false positive results. CDC also recommends that all providers clearly describe the strengths and weaknesses of rapid HIV tests to their clients, including the need to confirm reactive rapid tests.


Additional Resources


Footnotes

  1. Of the currently approved CLIA-waived rapid HIV tests, rapid tests performed on blood are slightly better at detecting true positive specimens (i.e., greater sensitivity) than oral fluid rapid tests. Three of the whole blood rapid tests perform better than the oral fluid test for correctly identifying negative specimens as negative (specificity), and one performs slightly less well. All of the differences between tests are small. Detailed comparisons of the sensitivity and specificity of currently approved rapid HIV tests can be found on the FDA-Approved Rapid HIV Antibody Screening Tests page.


  
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This article was provided by U.S. Centers for Disease Control and Prevention. Visit the CDC's website to find out more about their activities, publications and services.
 
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