Validation of reflex testing rules and establishment of a new workflow for body fluid cell analysis using a Sysmex XN-550 automatic hematology analyzer

Introduction: We developed and validated reflex testing rules for the microscopic examination (ME) of body fluids (BFs) on the Sysmex XN-550 (Sysmex Corporation) instrument. Methods: We assessed the detection limits, precision, linearity, and carryover. To develop the reflex testing rules (derivation arm), we tested 515 samples and then validated the rules using another 507 samples (validation arm). Results: All analytical performances were acceptable, and the carryover was negligible. There was agreement between the automated count and ME of red blood cells (r=.98) and total nucleated cells (TNCs) (r=.98), as well as the differential counts of neutrophils (r=.90) and lymphocytes (r=.84). We developed reflex testing rules: TNCs < 10/mu L, cell 2/cell 1 ratio <= 0.7, HF-BF cells > 7.9/100 white blood cells, LY-X >= 85 or LY-Y >= 90, and eosinophils > 2.5%. In the validation arm, implementation of the rules resulted in 126 rule-negative samples (24.9%) that were well correlated between the 2 methods. We propose a new workflow for BF cell analysis based on automated counting. Conclusion: The Sysmex XN-550 can be a suitable alternative to ME for BF cell analysis, especially for screening samples and subsequent automatic reporting under the rational use of laboratory-specific rules.