Pooled Testing for Virologic Monitoring?

A study conducted in South Africa indicates that pooling strategies could substantially reduce the cost of virologic monitoring while preserving accuracy.

Viral-load testing is critical for detecting HIV treatment failure but is rarely used in resource-limited settings because of the high costs and the requirement for sophisticated laboratory infrastructure. Pooled HIV RNA testing might be a viable alternative, according to a recent study from South Africa. Such testing has previously proven accurate and efficient for screening blood donors, diagnosing acute HIV infection, and detecting virologic failure in patients on antiretroviral therapy.

In the first part of the study, the researchers sought to develop criteria for identifying individuals who had a low probability of virologic failure (<10%) and would thus be eligible for pooled testing. They retrospectively analyzed information that is routinely included on laboratory request forms and found two pertinent variables: age ≥15 years and treatment with a regimen containing a nonnucleoside reverse transcriptase inhibitor.

The researchers then used two different pooling strategies (matrix and minipools) to evaluate stored specimens from individuals deemed to be at low risk for virologic failure. Four hundred liquid plasma samples were tested in minipools, and 300 of them were tested by matrix. The two strategies reduced the number of tests required by 31% and 41%, respectively, compared with individual testing. Based on current South African costs, using these strategies could lead to a savings in reagent costs of up to US$1640 per 100 specimens. Dried specimens were also tested using minipooling, and use of dried plasma spots was found to be the most efficient of any strategy analyzed.

Comment: Given the poor performance of clinical and laboratory algorithms to identify virologic failure, as well as limitations in laboratory infrastructure and human resources, accurate detection of treatment failure in many developing countries will be possible only when inexpensive point-of-care tests become available. In the meantime, optimization of algorithms that identify patients with a low probability of virologic failure and the use of pooled testing on dried plasma spots from such individuals might allow for wider access to viral-load monitoring, without increasing the number of tests performed or requiring an expansion of the existing laboratory infrastructure.

— Mauro Schechter, MD, PhD

Dr. Schechter is a Professor of Infectious Diseases at Universidade Federal do Rio de Janeiro, Head of the AIDS Research Laboratory at Hospital Universitario Clementino Fraga Filho, and Principal Investigator of Projeto Praça Onze at Hospital Escola São Francisco de Assis in Brazil. He reports no conflicts of interest.

Published in Journal Watch HIV/AIDS Clinical Care January 31, 2011

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