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False-Positive Results on Rapid HIV-Antibody Tests

Counselors at several HIV testing programs have reported a higher-than-expected rate of false-positive results with the OraQuick oral fluid test. The CDC, FDA, and test manufacturer are investigating.

The OraQuick Advance Rapid HIV-1/2 Antibody Test (OraSure Technologies, Bethlehem, Pennsylvania) can be done by trained personnel as a point-of-care test for HIV antibody in oral fluid. These characteristics obviate the need for blood drawing and the use of a central laboratory, and the rapid turnaround allows providers to give negative results to their patients during the same visit (ACC Mar 1 2003). However, reactive tests are considered preliminary and must be confirmed by standard HIV-antibody testing, which in most cases involves a screening ELISA and, if this is positive, a confirmatory Western blot. The published specificity for the OraQuick oral-fluid test — that is, the likelihood that a person without HIV will have a negative test — is 99.8% (95% confidence interval, 99.6%–99.9%). The sensitivity — the likelihood that a person with HIV will test positive — is 99.3% (95% CI, 98.4%–99.7%).

In late 2005, counselors at several HIV testing programs (mainly in New York City and San Francisco) reported apparent clusters of positive OraQuick HIV test results on oral fluid that were ultimately found to be negative on confirmatory testing. At some locations, the reported rate of false-positive test results was as high as 9 per 1000, which is higher than the 2 per 1000 expected with a specificity of 99.8%. In response to these reports, the CDC, FDA, and test manufacturer are investigating whether changes in the testing protocol are indicated. For now, the FDA believes that use of OraQuick should proceed, as long as users are informed of the need for additional testing to confirm reactive rapid tests.

Comment: The availability of a rapid HIV antibody test that does not require a blood draw or fingerstick was a major advance in HIV testing and has been widely adopted by counseling and testing sites. Whether the test is actually performing worse than predicted by published estimates of specificity remains unclear, although this possibility is suggested by the recent reports. Another possibility is that the counselors are uncomfortable giving test results that are positive but not confirmed, a position they had not been in previously with the standard ELISA/Western blot two-step procedure. (Notably, ELISA testing might have a false-positive rate as high as 2%, and counselors did not report positive ELISA results to patients if they were not confirmed.) Perhaps a better term for a "positive" rapid-test result would be "inconclusive," which better describes the need for further testing to obtain a definitive result.

— Paul E. Sax, MD

Published in Journal Watch HIV/AIDS Clinical Care January 4, 2006

Citation(s):

Centers for Disease Control and Prevention. Supplemental testing for confirmation of reactive oral fluid rapid HIV antibody tests. MMWR Morb Mortal Wkly Rep 2005 Dec 23; 54:1287-8.

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