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31-01-2012 | Immunology | Article

Oral HIV test may not be suitable in low-prevalence populations


Free abstract

MedWire News: Results of a systematic review and meta-analysis show that the positive predictive value (PPV) of the Oraquick rapid point-of-care HIV test is lower with oral fluid than with whole blood specimens when used in populations with a low prevalence of HIV.

This finding "needs to be considered in the widespread implementation of HIV testing, including home-based testing, self-testing, or over-the-counter testing initiatives, in all low-prevalence settings," caution Nitika Pant Pai (McGill University Health Centre, Montreal, Quebec, Canada) and colleagues.

By contrast, the PPV was similar for the two specimen types in high-prevalence settings, and the overall specificity of the test was also similar when using oral fluid or whole-blood samples. The sensitivity, however, was slightly lower with oral fluid than with whole blood, the researchers report.

In 2004, the US Food and Drug Administration approved the Oraquick advance rapid HIV-1/2 test (OraSure Technologies Inc, Pennsylvania, USA) for use with specimens of oral mucosal transudate, in addition to having previously approved it for use with whole-blood specimens.

It has since become one of the most popular HIV point-of-care tests based on oral specimens, possibly because of its noninvasive, pain-free specimen collection and rapid turnaround time, say the researchers.

The test is currently being considered for potential use as an "over-the-counter test" in the USA and in many sub-Saharan countries, but until now, there has not been a review of its worldwide accuracy.

To address this, Pai and team searched published literature and data from five major HIV conferences for studies that compared the diagnostic accuracy of the Oraquick test when used with oral versus whole blood specimens in adults at risk for HIV.

Data from seven studies reporting direct head-to-head comparisons of the two specimen types showed that pooled sensitivity was about 2% lower in oral (98.0%) than in blood-based specimens (99.7%), but specificity was similar (oral 99.7%; blood 99.9%).

"The lower sensitivity of the test in oral mucosal transudate compared with blood specimens is probably because of a lower quantity of HIV antibodies in oral mucosal transudate than in whole blood," the researchers remark.

When calculating the PPV of the test, the team looked at performance in populations with high (>1%) and low prevalence (=1%) of HIV. Examples of high-prevalence populations include intravenous drug users, sex workers, and men who have sex with men, while low-prevalence populations include outpatients from general clinics.

They found that the PPVs were similar for oral and whole blood specimens in high-prevalence settings, at 98.7% and 98.5%, respectively, but were lower for oral fluid than whole blood (88.6 vs 97.7%) when the prevalence of HIV was low.

"To put this in context, although the oral test is popular because of its convenience and ease of specimen collection, compared with the blood-based test, the use of a single oral test in low-prevalence settings could lead to a higher number of false positives than blood-based testing," write the researchers in the Lancet Infectious Diseases.

Furthermore, "because Oraquick is a screening test, information on the importance of confirmatory testing must be built in or emphasised for a positive test, irrespective of specimen type."

"This confirmation is especially important in a low-prevalence or low-risk population, such as in pregnant women in most worldwide settings," Pai et al conclude.

By Laura Cowen

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