Saliva HIV Tests Showing False-Positives in NYC
If you’ve taken an HIV test, and have taken the 20 minute tests, you know there are two kinds: The finger prick test, and then the cheek-swab test. Well, NYC Department of Health has recently suspended use of the latter test because of a 3 year history of false-positives, according to the Centers for Disease Control and Prevention’s latest MMWR (Morbidity & Mortality Weekly Report). They write:
The cause for the episodic increases in false-positive oral fluid tests has not yet been determined. NYC DOHMH has again suspended the use of oral fluid testing in STD clinics, and finger-stick whole-blood testing is the only rapid HIV test being used in this setting. These findings underscore the importance of confirming all reactive HIV tests, both from oral fluid and whole-blood specimens. In addition, the results suggest that the NYC DOHMH strategy of following up reactive oral fluid test results with an immediate finger-stick whole-blood test reduced the number of apparent false-positive oral fluid test results and might be a useful strategy in other settings and locations.
Testing with blood is simply more reliable, but the CDC goes on to explain why they still recommend the use of the saliva based HIV test:
CDC continues to encourage the use of rapid HIV tests because they increase the number of persons who are tested and who receive their test results. Six rapid HIV tests have been approved by FDA since 2002 (10). The New York City data indicate that repeating a rapid test on finger-stick whole blood after receiving a reactive oral fluid test result allows clinic counselors to provide more accurate test-result information to patients while minimizing the number of finger-stick tests that must be performed. Regardless, confirmatory testing is required to confirm both oral fluid and whole-blood reactive rapid HIV tests. Before testing, all patients should be informed that reactive rapid HIV test results are preliminary and require confirmation. 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.
Overall, oral fluid rapid tests have performed well and make HIV testing possible in many venues where performing phlebotomy or finger sticks is impractical for screening. However, users should be aware of the unexplained variability in the rate of false-positive test results. CDC will continue to work with FDA and the manufacturer to investigate the causes and extent of increases in false-positive oral fluid tests, monitor the performance of oral fluid and other rapid tests to ensure that they continue to perform as expected in testing programs, and investigate other combination test strategies to minimize false-positive test results.
I hate giving blood, but if you can help it, get the finger-prick test. It’s really not painful and seems to be more reliable. Getting blood drawn is probably still the best way, but waiting for days on end for lab results is nerve wrecking, so I only do those when I get an annual physical and blood work done with my doctor. Even if you get a positive result any of the rapid tests, they will always do a blood draw to confirm the results, which is why they know the saliva test was giving a higher rate of false positives.