Quantification of parasite density in 200 microscopic fields underestimates the parasitemia level in malaria patients.

The determination of parasitemia in the diagnosis of malaria is a routine practice because it assists the selection of treatment. The techniques used for estimating parasitemia are based on leukocyte counts or on a fixed volume of blood examined in a microscopic field. This study evaluated the concordance between parasitemia estimated by counting parasites in 200 microscopic fields and by counting parasites per 500 leukocytes using the automated leukocyte count as a reference. This study included 403 patients with acute malaria. The parasitemia levels obtained by each method varied greatly. A large discrepancy was observed between the 2 methods with respect to parasitemia results, with 17.6% and 82.4% of the values being overestimates and underestimates, respectively, compared to quantification by the automated leukocyte counts. Thus, these findings reveal the inaccuracy of this method and should be considered by health professionals involved in clinical management of the disease.