Enhancing Blast Detection in Leukopenic Patients by Identifying Apoptotic Regions in the Sysmex XN-Series WPC Scattergram.

Background: The white cell precursor (WPC) channel of the Sysmex XN-series hematology analyzer, which is designed for blast detection, showed reduced sensitivity for blast detection in leukopenic patients undergoing chemotherapy. This study aimed to evaluate the gating region for apoptotic blasts in the WPC scattergram to enhance detection sensitivity.

Methods: NOMO-1 cells, a human acute monoblastic leukemia cell line, were treated with varying concentrations of cytarabine (0, 100, 500, and 1,000 nM) for three days to induce apoptosis. Apoptotic cells were identified using annexin V and propidium iodide staining and were analyzed by flow cytometry to distinguish early and late apoptosis. Treated cells were mixed with normal blood and analyzed using the WPC scattergram to compare their gating regions with the reference region.

Results: Treatment with 1,000 nM cytarabine induced significant apoptosis in NOMO-1 cells, with 30.79% under-going early apoptosis and 38.44% late apoptosis, compared to untreated cells (4.52% early, 5.12% late). Apoptotic NOMO-1 cells were consistently localized in the lower-middle region of the WPC scattergram, distinct from the predefined reference gating region. This pattern persisted in mixed blood samples, confirming their consistent po-sitioning outside the reference gating region.

Conclusions: Apoptotic NOMO-1 cells exhibited reduced forward scatter light, side fluorescence light, and side scatter light signals in the WPC scattergram. Incorporating this region into gating strategies may enhance the sensitivity for detecting atypical blasts following chemotherapy, particularly when Wright-Giemsa stains reveal blasts without a corresponding 'Blast?' flag.