Tuesday, May 26, 2015

Are Rapid HIV-1 Antibody Tests Prone To Inaccuracies?

Even though over-the-counter kits had been available for sometime now, are rapid HIV-1 antibody tests still “prone to inaccuracy problems”?

By: Ringo Bones

Even before it’s over-the counter kit counterparts were granted approval, rapid HIV-1 antibody tests had been providing “point of care” results that made the need of laboratory facilities unnecessary, but researchers in Uganda have found out some time ago that such tests could result in “possible misrepresentation of results”. R.H. Gray and his team had noticed in practice of the limitations of rapid HIV-1 antibody tests during screening for trials in Uganda diagnostic test accuracy study that was published in the British Medical Journal back in 2007.   

A total of 1,517 males aged 15 to 49 years of age were screened for trials of circumcision to prevent HIV infection. They used an algorithm with three different rapid tests – i.e. first test negative – HIV-negative diagnosis; first and second test positive – HIV positive; first test positive, second test negative – diagnosis based on result of third test. These diagnoses were compared with diagnoses based on enzyme immunoassay and western blotting.

The sensitivity of the rapid tests for a diagnosis of HIV infections was 98-percent. The strength of any positive bands was coded for 639 samples. Among these samples, 125 tested positive and 37 of these were weak-positive. In this subgroup of 639 samples, the specificity was only 94-percent and the positive predictive value of 74-percent (26-percent false-positives). Among the 37 samples that were weakly positive, 86-percent were HIV-negative on laboratory testing and 8-percent gave indeterminate results on western blotting. When the 37 weak-positives were excluded, specificity was almost 100-percent, as in 99.6-percent, and the positive predictive value was 98-percent. Given the “convoluted statistics”, weak-positive bands on rapid tests should be confirmed by enzyme immunoassay and western blotting. Standard serological assays should be used for quality control in all programmes using rapid HIV-1 antibody tests.

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