Evaluation of body fluid mode of Sysmex XN-9000 for white blood cell counts in cerebrospinal fluid

Background: This study was planned to evaluate the analytical performance of the novel and fully automated Sysmex XN-9000 analyzer for rapid analysis of cerebrospinal fluid (CSF) samples. Methods: Forty-four CSF samples were used for method comparison studies between Sysmex XN-9000 body fluid mode and conventional optical microscopy. The bias between data obtained with the two methods was estimated with Bland-Altman plot analysis. The analytical evaluation also included the assessment of imprecision, linearity and carry-over. Results: A good agreement was found between results obtained with Sysmex XN-9000 body fluid mode and optical microscopy. The mean bias was 1.6×106 cells/L for total white blood cells (95% CI: −21.8×106 to 25.1×106 cells/L), 1.3×106 cells/L for polymorphonuclear cells (95% CI: −13.9×106 to 16.5×106 cells/L) and −0.6×106 cells/L for mononuclear cells (95% CI: −21.5×106 to 20.3×106 cells/L). The carryover was found to be lower than 0.01% and the imprecision was lower than 5%. The XN-9000 body fluid mode was also characterized by excellent linearity in the range of values comprised between 85×106–3,197×106 cells/L, with correlation coefficients (r) always equal to 1.00 (P<0.001). Conclusions: The Sysmex XN-9000 body fluid mode displays excellent analytical performance in terms of imprecision, linearity, carry-over and comparability with conventional optical microscopy, so that it may be used as a first-line, screening technique for rapid analysis of CSF samples referred for both routine and, especially, for urgent testing.