Researchers at Wistar Institute and the University of Massachusetts, Amherst, with global collaborators, introduce a new "prediction-based classification" system that could potentially reduce the burden of monitoring patients on antiretroviral therapy (ART) experienced by medical laboratories in developing nations. This mathematical system can predict which patients on ART may not experience a rise in CD4 T cells (a type of white blood cell), thereby allocating tests only to those who may need it and potentially eliminating nearly 54 percent of unnecessary CD4 tests. A CD4 count is the standard marker for immune recovery after ART treatment as a reliable indicator of patient health, but it is also a capacity and resource-intensive process. This algorithm could be used as a triage tool to direct available laboratory CD4 testing capacity to high-priority individuals, that is, those likely to experience a dangerously low CD4 count.