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Rapid HIV Testing in Emergency Departments — Beware of False Positives

In a low-prevalence ED, rapid tests often ruled out HIV, but, when reactive, they often yielded false-positive results.

In 2006, the CDC recommended routine HIV testing for all adults and adolescents in all healthcare settings, including emergency departments (EDs; AIDS Clin Care Oct 6 2006). This recommendation, coupled with the availability of rapid HIV tests, has resulted in a variety of efforts to increase HIV screening in EDs. However, many concerns remain (JAMA 2008; 300:945), such as the feasibility of testing in this setting, mainly because of the resources required (AIDS Clin Care Jan 14 2008), and the specificity of rapid oral-fluid tests (AIDS Clin Care Jul 7 2008).

In the present study, investigators evaluated the performance of the OraQuick Advance Rapid HIV-1/2 Antibody Test in the context of a clinical trial conducted in a busy ED in Boston. All rapid tests were performed using oral fluid, and all reactive tests were followed by a Western blot, an EIA, and measurement of both CD4-cell count and plasma viral load.

During an 8-month period in 2007, 2356 ED patients were invited to participate in the HIV testing trial; 1397 (59.3%) agreed. Of the 854 who actually underwent rapid testing, 849 had interpretable results. Thirty-nine patients (4.6%) had reactive tests. Of the 31 who agreed to confirmatory testing, only 5 were found to be HIV-infected, for an overall HIV prevalence of 0.6%; the others were catalogued as not infected. In this setting, the estimated specificity of the test was 96.9% (95% confidence interval, 95.7%–98.1%), which was significantly lower than the specificity reported by the manufacturer (99.8%; 95% CI, 99.6%–99.9%).

Comment: This HIV testing program was considered a success, because many patients who otherwise would not have been tested left the ED knowing that they were not HIV-infected. However, we clearly need better ways to confirm or rule out the presence of HIV infection in patients whose rapid tests are reactive. The authors suggest including viral-load testing in the panel of confirmatory tests, along with Western blot and EIA.

— Carlos del Rio, MD

Published in AIDS Clinical Care September 8, 2008

Citation(s):

Walensky RP et al. Revising expectations from rapid HIV tests in the emergency department. Ann Intern Med 2008 Aug 5; 149:153.

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