Effects of different blood storage conditions on leukocytes cell population data using the Sysmex XN hematological analyzer

Introduction: The aim of this study was to investigate the stability of leukocyte cell population data (CPD) assessed on Sysmex XN-3000 hematological analyzer in samples stored for up to 24 h at different temperatures. Materials and methods: Whole-blood samples from 25 donors were analyzed for 18 CPD parameters at baseline and after storage at room temperature (RT), 4 °C, or 37 °C for 3, 6, 12, and 24 h. Stability was assessed using three complementary approaches: paired Wilcoxon tests with Bonferroni correction, percent difference between medians > 10%, and per-sample percent change > 10% in ≥ 2 samples. In addition, the European Federation of Clinical Chemistry and Laboratory Medicine (EFLM) stability protocol was applied, modelling percent differences over time using linear regression through the origin to estimate the rate of change and the stability limit (SL), defined as the time required to exceed a maximum permissible error of 10%. Results: According to predefined stability criteria, several CPD parameters exceeded stability limits within 24 h, particularly under storage at 37 °C. Parameters related to neutrophil, lymphocyte and monocyte complexity and size (e.g., neutrophils complexity (NE-SSC), neutrophils size (NE-FSC), monocytes complexity (MO-X), lymphocytes complexity (LY-X); where SSC = side scatter, FSC = forward scatter) showed slow rates of change with estimated stability limits beyond 24 h across storage conditions. In contrast, fluorescence- and dispersion-related parameters (e.g., neutrophils fluorescence intensity (NE-SFL), width of dispersion of neutrophils complexity (NE-WX), width of dispersion of lymphocytes fluorescence (LY-WY), width of dispersion of monocytes size (MO-WZ); where SFL = side fluorescence, W = width of dispersion) reached the stability limit within 24 h, most frequently at 37 °C. Lymphocyte size (LY-Z) exceeded the stability limit at 17 h also under storage at 4 °C. Conclusions: Leukocyte CPD stability is strongly temperature- and parameter-dependent. Exposure to elevated temperature (37 °C) leads to early exceedance of predefined stability limits for several CPD parameters, whereas storage at RT preserves stability for longer time intervals. Avoiding prolonged exposure to high temperatures is therefore essential for reliable CPD assessment in routine laboratory practice.