Diagnostic Performance of the Hematology Analyzer XN-31 for Detecting Plasmodium Infections in School-Based Surveillance in Western Kenya

Despite significant progress in malaria control, asymptomatic and submicroscopic infections remain important reservoirs sustaining transmission and are often undetected by conventional microscopy or rapid diagnostic tests (RDTs). The Automated Hematology Analyzer XN-31 (Sysmex, Kobe, Japan) has shown high diagnostic accuracy in clinical settings, but performance under active surveillance, particularly among asymptomatic individuals, has not been evaluated. In this study, we assessed XN-31 using samples from school-based active surveillance in western Kenya, where asymptomatic and submicroscopic infections are highly prevalent. Among 1,237 samples, 564 (45.6%) were positive for Plasmodium spp. by polymerase chain reaction (PCR), including 511 afebrile infections. Using PCR as the reference, XN-31 detected infections with a sensitivity of 70.2%, slightly higher than microscopy (65.1%), and a specificity of 98.4%, higher than RDT (79.8%) and similar to microscopy (98.7%). It detected 43 of 197 submicroscopic infections (21.8%), with a median parasite density of 57 parasites/ µ L (interquartile range: 38–202). XN-31 identified 11 of 76 mixed infections of Plasmodium falciparum and non- P. falciparum compared with 5 by microscopy and 0 by RDT. Importantly, it also detected 8 of 14 P. falciparum infections suspected to carry hrp2/3 deletions, which caused false-negative RDT results, comparable with microscopy. This is the first study to evaluate XN-31 for detecting asymptomatic infections, non- P. falciparum species, and hrp2/3 -deleted parasites, which are key diagnostic challenges in endemic settings. Our findings support the potential of XN-31 as a practical and reliable surveillance tool that bridges between RDTs and PCR for enhanced parasite detection and accelerated malaria control efforts.