Field diagnostic performance of the Sysmex XN31 automated hematology analyser for malaria screening among febrile children in a sentinel site for malaria surveillance site in Libreville, Gabon

OBJECTIVE: To evaluate the diagnostic performance of the Sysmex XN-31 haematology analyser for malaria detection in a sentinel site. METHODS: A prospective diagnostic assessment study was conducted among febrile children under 15 years of age, attending a sentinel site for malaria surveillance in Libreville, Gabon. Malaria diagnosis by the Sysmex XN-31 was compared with microscopy. Sensitivity, specificity, predictive values, likelihood ratios, and Cohen's kappa coefficient were calculated. Receiver operating characteristic (ROC) analysis was performed using the MI-RBC count as a continuous diagnostic score. Subgroup analyses were performed according to age group (<5 vs ≥5 years), parasite species, and parasite density categories. RESULTS: Among 1034 febrile participants, prevalence of malaria was 23.9% by microscopy and 24.3% via the XN-31 (p < 0.01). The overall sensitivity and specificity of the XN-31 were 98.4% (95% CI [96.9-99.9]) and 99.9% (95% CI [98.8-99.9]), respectively. Sensitivity was slightly lower in children under five years of age (96.9%, 95% CI [92.3-98.5]) and in cases of low parasitaemia (90.7%, 95% CI [82.0-99.3]).Statistical comparisons between subgroups showed no significant difference in diagnostic performance between age groups (all p > 0.05), while sensitivity was significantly lower at parasite densities below 100 parasites/µL than at higher densities (p = 0.030). Species identification demonstrated high concordance for P. falciparum, thirty samples were classified as 'UNC', of which approximately 80% were associated with low parasite densities. ROC analysis of the MI-RBC count showed an overall AUC of 0.991 (95% CI [0.984-0.997]), with an optimal diagnostic threshold of 20 parasites/µL. CONCLUSION: The Sysmex XN-31 demonstrated excellent overall diagnostic performance for malaria detection in an endemic setting. Despite reduced sensitivity at low parasitaemia and in children under five years of age, and limited species discrimination at low parasite densities, the Sysmex XN-31 represents a robust and appropriate complementary tool for malaria surveillance and clinical trials in endemic settings.