US CDC issue reports of false-positive oral rapid tests in New York HIV testing programme

The CDC is publishing important information in the Mortality and Morbidity Weekly Report (MMWR) about false-positive oral fluid rapid tests for HIV, reported in New York City between 2005 and 2008.

In the first 7 months after oral fluid testing was introduced, 35 (0.16%) of 21,722 tests were false positive by Western blot, consistent with the 99.8% (95% confidence interval [CI] = 99.6%-99.9%) specificity claim by the manufacturer in the product package insert. However, in October 2005, staff members at the clinics noticed an increase in the number of false-positive oral fluid test results each month.

From an average of five false-positive tests per month, the monthly number of false-positive tests increased to 11 (0.27% of 4,024 tests) in October 2005 and to 36 (0.97% of 3,735 tests) in November 2005 (with a specificity of 99.03%, lower than the lower limit of the manufacturer’s CI specifications).

Despite the increased number of false-positive results, testing with the noninvasive oral fluid specimens was popular with clinic patients and both testing rates and patients returning for results remained significantly higher than before they had been introduced.

However, in the period November 2007 to April 2008, nearly half of reactive oral fluid tests in the STD clinics were false positive, prompting a shift to using rapid finger-stick tests.

The information highlights the importance of confirmatory testing, as required by product labeling, 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.