Design of malaria diagnostic criteria for the Sysmex XE-2100 hematology analyzer

Abstract

Thick film, the standard diagnostic procedure for malaria, is not always ordered promptly. A failsafe diagnostic strategy using an XE-2100 analyzer is proposed, and for this strategy, malaria diagnostic models for the XE-2100 were developed and tested for accuracy. Two hundred eighty-one samples were distributed into Plasmodium vivax, P. falciparum, and acute febrile syndrome groups for model construction. Model validation was performed using 60% of malaria cases and a composite control group of samples from AFS and healthy participants from endemic and non-endemic regions. For P. vivax, two observer-dependent models (accuracy = 95.3-96.9%), one non-observer-dependent model using built-in variables (accuracy = 94.7%), and one non-observer-dependent model using new and built-in variables (accuracy = 96.8%) were developed. For P. falciparum, two non-observer-dependent models (accuracies = 85% and 89%) were developed. These models could be used by health personnel or be integrated as a malaria alarm for the XE-2100 to prompt early malaria microscopic diagnosis.

Figure 1.

Study design and sampling procedure. R, referred by physician; NR, not referred by physician; AFS, participant with malaria-negative acute febrile syndrome; HE, healthy participant from endemic region; HNE, healthy participant from non-endemic region. Details in text. *Diagnostic reference standard for malaria versus AFS. **Diagnostic reference standard for malaria versus healthy in composite control. ***Index test diagnostic criterion (optimal predicted probability obtained for each diagnostic model). Blood analysis from where data were obtained to construct the index diagnostic criteria.

Figure 2.

Summary images and level-edited summary images obtained using Photoshop CS3 for AFS (A and B) and P. vivax (C and D). White and yellow perimeter lines in A delimit the areas where scatterplot variables not given by the XE-2100 IPU where codified for analysis (Supplementary Panel 1). C depicts the general XE-2100 P. vivax pattern. Arabic numerals correspond to categorical variables: 1, neutrophil group, outside limit (yellow line); 2, neutrophil group, inferior deviation; 3, neutrophil group, right deviation; 4, eosinophil group, outside limit (yellow line); 5, confluent neutrophil and eosinophil groups; 6, granulocyte-coded events outside inferior limit; 7, number of neutrophil-coded group(s) (1 or 2); 8, number of eosinophil coded group(s) (1 or 2); 9, tendency of granulocytes to form one group; 10, abnormal granulocyte-coded group color (gray or normal); 11, gray RBC ghosts; 12, fusion of neutrophil group and RBC ghosts; 13, WBC blue group crosses limiting line; 14, high SFL gray events past limiting line. Variables 1–10 conform to the compound variable number of granulocyte-coded DIFF abnormalities. Roman numerals correspond to pixel counting areas [DIFF(I), DIFF(II), WBC/BASO(III), RET-EXT(IV), RET-EXT(V) and RET-EXT(VI))]. ^§C and D show the duplication (arrows) of neutrophil and eosinophil groups in the DIFF scatterplot and the fusion (bracket) of all granulocyte-coded events. Abnormal events in the WBC/BASO(III) counting area. **The wide IMI WBC ghost group. *The alinear pattern of fluorescent gray-coded events revealed in the level-edited summary image.

Figure 3.

Representative scatterplots of samples from A (AFS group), B–E (P. vivax group), and F (P. falciparum group). B–E show the generalXE-2100 P. vivax pattern. *Abnormal patterns are the granulocyte-coded events in the DIFF scatterplot. **The pixel-counting area in the WBC/BASO(III). ***The larger WBC ghost group in the IMI scatterplot. ¶The medium and low FSC linear patterns of gray-coded events in RET-EXT(V)and (VI). (F) Scatterplots from a P. falciparum sample showing the similarity with the AFS sample (A) and the lack of significant abnormalities.