Questions and Answers: False-Positive Oral Fluid Rapid HIV Tests
August 12, 2008
What is the significance of the reported increases in false positives when using the oral fluid HIV test in New York City sexually transmitted disease (STD) clinics?
It is important to keep in mind that overall oral fluid tests have performed well. The significance of the increase in false-positive oral fluid test results is not yet known. However, when the accuracy of a test varies like this in one site it is necessary to determine if it is a temporary event a site-specific issue, or a change in the way the test is working. A false-positive HIV test result is an emotional event for patients that can create anxiety over one's health and mistrust of the medical system. From a provider's standpoint, a pattern of increased false-positive test results from a specific test may create less confidence in the test and add more costs for confirmatory testing.
The increase reported in NYC STD clinics represents <1 percent of all reactive oral fluid rapid tests. From March 2005, when NYC DOHMH, began using oral fluid rapid testing, through May 2008, 0.27% (or 442) of the 166,058 oral fluid rapid HIV tests were false-positive with peaks in late 2005 and between November 2007 and April 2008. Despite these episodic elevated levels of false positive results, the oral fluid test has always performed above the Food and Drug Administration's minimum threshold of 98.0% specificity.
AdvertisementCDC is committed to ensuring patients get correct test results. Further investigation is needed into the NYC DOHMH experience; but it is critical to know that the oral fluid test followed by a confirmatory test, results in an accurate diagnosis and has shown success in reaching more people for testing. The first step to helping to ensure improved health for those infected and to help prevent transmission of HIV to others is knowing one's HIV infection status.
What is CDC doing about the increase in New York City?
CDC continues to work with the Food and Drug Administration and the manufacturer to
- Investigate the cause and extent of the increases in false-positive oral fluid tests,
- Monitor the performance of oral fluid and other rapid test to ensure they continue to perform as expected, and
- Look at other combination test strategies to minimize false-positive test results.
CDC also encourages
- All jurisdictions and organizations that use rapid HIV tests to report to the manufacturer and to CDC any false positive (or false negative) results.
- All providers that use the oral fluid rapid HIV test to explain clearly to patients the strengths and weaknesses of the test and the need to always receive an approved confirmatory test after an initial reactive rapid test.
Does CDC still recommend oral fluid rapid HIV tests?
Yes. CDC continues to encourage the use of oral fluid rapid HIV tests not only because they allow for testing to be done in many more settings then before, particularly non-clinical settings, but also because they offer the potential to increase the number of persons who are tested and who receive their test results. Further, CDC acknowledges that the oral fluid test has, to date, performed within FDA specifications. It is important to note, however, that users need to be aware of the potential for unexplained variability in the rate of false-positive test results and the need to follow a reactive (positive) oral fluid rapid test with a confirmatory test. Finally, before using any rapid HIV test, patients should be informed that reactive rapid HIV test results are preliminary and require confirmation.
What HIV testing practices are currently being used by the NYC STD clinics?
Since the second episode of false positive test results during November 2007 through May 2008, NYC STD clinics suspended the use of the oral fluid rapid HIV test. Currently, the clinics are using the finger-stick whole blood rapid HIV test, which has not shown increases in false positives.
What are the advantages of performing a rapid HIV test on blood after a reactive oral fluid test result?
Some programs, such as NYC's STD clinics, perform a follow-up test on finger-stick whole blood after a reactive oral fluid test. The strategy of follow-up blood testing allows counselors to give more accurate information based on both test results. This strategyperforming a finger-stick whole blood test after a reactive oral fluid testallowed NYC DOHMH to minimize the number of finger-stick tests that needed to be performed, and also to promptly identify the increase in false-positive oral fluid tests. In almost all cases, a reactive oral fluid test followed by a negative whole-blood test has proven to be false-positive by confirmatory testing. Confirmatory testing is still required after a reactive oral fluid rapid test, even when a follow-up whole blood rapid test is negative.
Why has NYC DOHMH discontinued the use of oral fluid rapid tests in its STD clinics, but continues to use them in other venues?
Because of the way the NYC DOHMH is structured, the STD clinics are separate from other types of clinics. The false-positive results were reported only in STD clinics; therefore, the decisions to stop oral fluid rapid HIV tests were limited to those clinics. As well, STD clinics have the capability to easily draw blood for testing. In general, testing with blood or serum specimens is more accurate than testing with oral fluid and is preferred when feasible, especially in settings where blood specimens already are obtained routinely.
Are there explanations for why these false-positive results occurred?
At this time, the cause of the increase has not been determined. NYC DOHMH reported that no consistent relationship was detected between false-positive results and test kit handling, storage conditions, or a particular group of tests used, or between false-positive results and clinic sites, test operators, or patient characteristics. More study is needed to find the reason for the increase in false-positive test results.
Have other jurisdictions reported increased numbers of false positive results from these tests?
CDC has not received any validated reports from other jurisdictions and is continuing to monitor this situation. This MMWR article is limited to New York City's experience. However, previous reports of elevated levels of false-positive results with oral fluid tests have been reported and investigated. CDC encourages the reporting of false-positive clusters related to the use of the oral fluid rapid HIV test to the Food and Drug Administration, to CDC, and to the manufacturer.