Malaria detection with the Sysmex XE-2100 hematology analyzer using pseudoeosinophilia and abnormal WBC scattergram

Recent investigation using the Sysmex XE-2100 hematology analyzer (Sysmex Corporation, Japan) has demonstrated erroneously high eosinophil counts and abnormal white blood cell (WBC) scattergrams in malaria cases. This study was conducted to assess the diagnostic efficiency of the Sysmex XE-2100 analyzer for malaria. One hundred forty-four patients initially diagnosed with Plasmodium vivax infection, 319 patients with febrile illness, and 24 patients who underwent malaria treatment were analyzed. Atypical features on Sysmex XE-2100 analyzer were categorized as pseudoeosinophilia (a gap of more than 5% in eosinophil counts between the Sysmex XE-2100 analyzer and microscopic examination) and abnormal WBC scattergram. Pseudoeosinophilia or abnormal WBC scattergram were detected in 100 of 144 malaria-positive samples (sensitivity 69.4%, specificity 100%). The samples with pseudoeosinophilia or abnormal WBC scattergrams showed significantly higher parasite counts than the samples without pseudoeosinophilia or an abnormal WBC scattergram (P<0.05). All 24 samples from patients for whom the malaria smear was repeated after malaria treatment was initiated showed a normalized eosinophil count and a normal WBC histogram. In conclusion, attention to differential count and WBC scattergrams provided by the Sysmex XE-2100 would be a valuable tool in malaria detection.