Performance of the Sysmex White Precursor Channel to discover circulating leukemic blast cells

INTRODUCTION: Circulating immature precursor cells indicate malignant diseases like acute myeloid or lymphoid leukemia, and blast cells are key finds for disease management. Automatized cell counters are an essential contemporary appliance for blast detection, but false-positive samples remain challenging in terms of time and resources. To reduce this issue, the White Precursor Channel (WPC) was introduced to Sysmex XN series; however, sensitivity may reduce when accommodating low specificity. Therefore, our aim was to evaluate WPC blast alarm flag performance with regard to detecting blast cells.

METHODS: At two major Danish hospitals, random blood samples were collected from the routine setting in a four-week period and analyzed on WPC XN20 (Sysmex, Japan). Results were compared with manual differential white blood cell count (Manual WBCC) assisted by CellaVisionDM96.

RESULTS: In 117 samples, we found 0.2 to 34.4% blasts, WPC blast flag specificity = 82% and a low sensitivity = 40%. However, other XN alarm flags forwarded samples to Manual WBCC, so blast cells were detected despite missing a specific blast flag: With all alarm flags, combined sensitivity increased to 88%. Overall, the WPC application stopped 18% of the 117 samples going to Manual WBCC (three false negatives). Q values are arbitrary probability measurements for the blast flag, and in five samples (0.5 to 47.3% blasts) imprecision ranged from 5.3 to 122 CV%.

CONCLUSIONS: WPC blast alarm flags are imprecise and inaccurate, especially when blast counts are low. However, the XN20 will alarm samples with other flags so that most samples containing blast cells will be manually reviewed after all. Hence, the presented flag types should not bias the decisions of manual reviewers.