Pseudoeosinophilia associated with malaria infection determined in the Sysmex XE-2100 hematology analyzer

Hemozoin is known to be an end product of hemoglobin digestion by the malaria parasite. Hemozoin is a birefringent crystal, and thus hemozoin-containing white blood cells (WBCs) may show the atypical light scattering pattern. The purpose of this study was to investigate pseudoeosinophilia associated with malaria infection using a Sysmex XE-2100 hematology analyzer (Sysmex Corporation, Kobe, Japan). The study group included 16 patients with malaria infection. Of these, 38% showed erroneously high eosinophil counts and atypical eosinophil distributions in the WBCs scattergram, which was due to the presence of hemozoin-containing neutrophils. In two patients, their erroneously high eosinophil counts declined as the parasitemia decreased with treatment. In conclusion, hematologists should consider the possibility of pseudoeosinophilia as a result of hemozoin-containing WBCs and confirm the WBC differential count by microscopy in cases of malaria infection.