Verification of Patient Result Comparability Among Nine Hematology Analyzers Using the CLSI EP31 ‐A‐ IR Guideline: A Four‐Year Experience

INTRODUCTION: Clinical laboratories operating multiple analyzers with random sample allocation must ensure result comparability across instruments to support consistent clinical interpretation and patient safety. OBJECTIVES: To evaluate the applicability of the CLSI EP31-A-IR guideline for periodic verification of patient result comparability across multiple hematology analyzers, and to assess the longitudinal stability of this model over a four-year period. METHODS: Comparability of nine DxH-900 hematology analyzers (Beckman Coulter) was evaluated for 17 parameters, including complete blood count variables, leukocyte differentials, monocyte distribution width (MDW), and reticulocytes. Following the EP31-A-IR framework, approximate target concentrations were estimated from internal quality control data at three concentration levels to guide the selection of native patient samples covering clinically relevant ranges, including samples from oncohematological and sepsis-suspected patients. Acceptance criteria (AC) based on biological variation (BV) were established for each parameter and concentration level. The maximum allowable difference (MAD), as well as the number of runs and replicates, were calculated accordingly. Results were considered comparable when the maximum observed difference (MOD) was less than or equal to the MAD. RESULTS: For all 17 parameters evaluated, including reticulocytes assessed on a subset of four analyzers reflecting routine workflow, the MOD between instruments remained within predefined acceptance limits at all concentration levels. Longitudinal monitoring over a four-year period (2022-2025) demonstrated sustained inter-analyzer agreement, with no evidence of progressive analytical drift. CONCLUSIONS: The EP31-A-IR guideline proved to be a flexible and effective framework for periodic verification of patient result comparability in high-volume hematology laboratories. This study represents one of the first implementations of this guideline in the field of hematology, supporting reliable clinical interpretation across analytical platforms and fulfilling ISO 15189 accreditation requirements.