PEP talk: Rapid HIV tests make a quick comeback
August 1, 2001 4 minutes read
PEP talk: Rapid HIV tests make a quick comeback
CDC calls use of more than one rapid test ideal
Rapid HIV tests will once again allow hospitals to quickly determine the need for post-exposure prophylaxis (PEP) after needlesticks. The Abbott Murex Single Use Diagnostic System (SUDS) HIV-1 test, the only rapid HIV test currently licensed for the U.S. market, was re-released in May. It had been withdrawn in October due to manufacturing problems. Meanwhile, both the Centers for Disease Control and Prevention and the Food and Drug Administration (FDA) are encouraging the entry of other HIV tests into the U.S. market. About 60 rapid HIV tests are available in other countries.
By using more than one rapid HIV test, hospitals could reduce the likelihood of false positives and improve confidence in the test, says Bernard Branson, MD, a medical epidemiologist in CDC’s division of HIV/AIDS prevention. "CDC’s interest, in general, is to have several rapid tests, preferably those that are very similar," he says. "Ultimately, [we would want] a mechanism in which we can use rapid tests in combination to improve the predictive value of a positive HIV test result."
Rapid HIV tests offer results in as little as 10 or 15 minutes, allowing clinicians to respond quickly with appropriate PEP. However, HIV experts remain concerned about false positives and unnecessary use of PEP in low-prevalence populations.
If the specificity of the test is 99.6%, that means "four out a thousand will be false positives," notes Branson. Suppose a low-prevalence area has an HIV rate of .4%, or four out of a thousand in the population. In that case, the testing of a thousand people would produce four true positives and four false positives, he explains. "Half of your positives would be false positives."
That problem can be resolved by using more than one type of rapid HIV test, he says. "If the first [test] was positive, you would retest with the second one. If they’re both positive, you have a very high degree of confidence that it’s truly positive."
In rare cases, a hospital might need a third rapid HIV test to resolve a discrepancy between the two, he says. "The majority would only need to be tested once," Branson says. "A positive would need to be tested and, if those two disagreed, it would need to be tested a third time."
For the first time, the use of multiple rapid HIV tests is possible, at least for some hospitals. Trinity Biotech in Dublin, Ireland, received an Investigational Device Exemption for its Uni-Gold HIV test and is recruiting 20 hospitals to participate in the limited trial.
The Uni-Gold, which is used worldwide but has not yet been approved by the FDA, has a simple protocol and produces results in about 10 minutes, says Ron Cruver, Uni-Gold product development manager for Trinity Biotech USA in Jamestown, NY. In an effort to streamline the approval process, the FDA has redefined the requirements for rapid HIV tests, he says. "[The FDA] more clearly defined the number of positives and negatives you have to have and the specificity and sensitivity you have to meet," he says. "It helps the process to know exactly what’s expected out of the clinical trial."
The CDC has been conducting comparative studies on six investigational tests, including the Uni-Gold. "We are making that data available to the manufacturers if they wish to use them when they submit for FDA approval," says Branson.
Hospitals also are reporting their results with the currently available SUDS test. At the University of Virginia (UVA) Health System in Charlottesville, in a low HIV-prevalence area, 884 SUDS tests performed after needlesticks from January 1999 to September 2000 produced only one false positive, says Heidi Flanagan, RN, HIV and bloodborne pathogen coordinator.
While the SUDS test was off the market, 132 tests of source patients using the conventional EIA (enzyme-linked immunoassay) test also produced one false positive, says Flanagan, who presented her results at the April meeting of the Society for Healthcare Epidemiology of America. No one in the UVA health system has seroconverted to HIV following a needlestick, she says. But the speed of the rapid test helped allay fears, Flanagan says. "It gave a measure of assurance that the source patient was negative," she says. "We didn’t have to unnecessarily start post-exposure prophylaxis while we were waiting for the regular Elisa test to come back.
Even with rapid HIV tests, the CDC recommends follow-up testing with an EIA, Branson says. "We would still recommend that the blood sample was tested using conventional tests," he says. "But when you’re making that PEP decision, you want to take action as soon as you can.
"The conventional tests have been around for 17 years," he explains. "Until we have a lot more experience with the [rapid tests], we want to make sure they’re accurate."
(Editor’s note: Information about the Uni-Gold IDE is available on the Trinity web site, www.trinitybiotech.com.)
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