Is flow cytometry better in counting malaria pigment-containing leukocytes compared to microscopy?

Abstract

Background: Detection of malaria pigment (or haemozoin; Hz)-containing leukocytes may have prognostic relevance in malaria; however, studies reported conflicting results, with microscopic counts suggestive of being inaccurate and imprecise.

Methods: Numbers of Hz-containing leukocytes from a malaria patient obtained with a flow cytometer counting 50.000 gated events were compared with thin film microscopy as applied under field conditions.

Results: Flow cytometry identified 5.8% Hz-containing monocytes and 1.8% Hz-containing neutrophils. The microscopic examination yielded 10% and 13% of Hz-containing monocytes, as well as 0% and 0.5% of Hz-containing neutrophils for observers one and two, respectively.

Conclusion: Novel, robust and affordable cytometric methods should be evaluated in the field as they may assist in utilizing Hz-containing cells as clinically useful parameter.

Figure 1

Comparison of flow cytometric and microscopic determination of Hz-containing leukocytes (panel A, monocytes; panel B, granulocytes). 152 samples from malarious patients were used as part of a study on flow cytometric detection of Hz-containing leukocytes [5]. Hz-containing leukocytes were determined by counting 100 monocytes and 200 granulocytes in a thick film, and by image analysis of screenshot from a Cell-Dyn^® haematology analyser, as described elsewhere [5]. To allow better scaling in panel A, four outliers were excluded with 173/30, 167/53, 128/33 and 111/50 flow cytometric/microscopic monocyte counts, respectively.