Utility of Point-of-Care Malaria Rapid Diagnostic Tests

In their short report on the utility of a point-of-care malaria rapid diagnostic test (RDT) in HIV-infected adults, Mills and others conclude that “the rapid diagnostic test accurately ruled “in or out” malaria.” 1 However, at a positive predictive value of 70.6% and a lower confidence limit of 44.0%, it is difficult to state that the test accurately rules in malaria. At the “rule out” side, there is a moderate sensitivity of 85.7%, again with a disappointing lower confidence limit of 57.2%, which is caused by the low number of malaria cases. The high negative predictive value is probably caused by low pre-test probability (or malaria prevalence) in the study population (14 of 246, 5.6%). Thus, the probability of not having malaria before the test was already 94.4%, and the diagnostic gain offered by the RDT is limited to 4.7%. Malaria is a life-threatening disease that requires prompt and adequate treatment. Two of 14 cases were missed; the confidence limits indicate that it might have been six. Rapid diagnostic tests can miss not only low parasite densities such as in the present study, 2 but also high parasite densities caused by the prozone effect. 3