Saliva Test for HIV Compared with Blood Test

The oral HIV test has become one of the most popular tests because of its acceptability, ease of use and it is noninvasive, pain-free, and convenient and produces results in 20 minutes.

A meta-analysis carried out by scientists at the McGill University (Montreal, QC, Canada) compared studies worldwide, showed that the saliva HIV test, had the same accuracy as the blood test for high-risk populations. They computed the positive predicted values (PPVs) separately for specimens of oral mucosal transudate and whole blood and explored the variability of the PPV within specimen groups in low-prevalence and high-prevalence settings.

The low-prevalence setting was on the basis of estimates of seropositivity from each study and set at a conservative prevalence of disease in the study sample of less than or equal to 1%. Populations in this group included outpatients from general clinics and general population-based surveys. The high-prevalence setting was defined as one with a greater than 1% prevalence of disease in the study sample. Populations in this group included intravenous drug users, sex workers, those who attended clinics for sexually transmitted diseases, men who have sex with men, incarcerated populations, and pregnant women.

The results of the analysis showed that the saliva HIV test, the OraQuick advance rapid HIV-1/2 (OraSure Technologies Inc.; PA, USA) had the same accuracy as the blood test for high-risk populations. The test sensitivity was slightly reduced for low risk populations. The slightly 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 titer of HIV antibodies is also low in acute HIV infection before seroconversion, hence the increased possibility that oral testing might miss more acute HIV infections than tests with blood specimens because of its lower sensitivity.

Nitika Pant Pai, MD, an assistant professor of Medicine at McGill University, said, "Testing is the cornerstone of prevention, treatment and care strategies. Although previous studies have shown that the oral fluid-based OraQuick HIV1/2 test has great promise, ours is the first to evaluate its potential at a global level." Although Oraquick had a high PPV in high-prevalence settings in oral specimens, the slightly lower sensitivity and PPV in low-prevalence settings in oral specimens should be carefully reviewed when planning worldwide expanded initiatives with this popular test.

The study was published on January 24, 2012 in the Lancet Infectious Diseases.

Related Links:
McGill University
OraSure Technologies Inc.