Population-specific pediatric reference intervals for complete blood count in Vietnamese children and their impact on clinical classification

Abstract Objectives To establish age- and sex-specific reference intervals (RI) for complete blood count (CBC) parameters in healthy Vietnamese children aged 0 to <19 years and assess the impact of applying locally derived vs. non-local pediatric RI on abnormal flagging and clinical classification. Methods A community-based cross-sectional study included 3,885 healthy Vietnamese children aged 0 to <19 years recruited through school-based health screening programs between April 2024 and November 2025. Peripheral venous blood samples were analyzed using the Sysmex XN-9000 hematology analyzer under standardized pre-analytical and analytical conditions with internal and external quality control. Outliers were excluded using the Tukey interquartile range method. Age and sex partitions were established through an integrated assessment of visual inspection, the Mann–Whitney U test, Cliff’s delta, the Harris–Boyd method, and biological and clinical considerations. Reference intervals were established according to CLSI EP28-A3c using a nonparametric approach (2.5–97.5th percentiles), with 90 % confidence intervals estimated by bootstrap. Results All CBC parameters showed age-related variation, supporting age-specific RI. Sex differences were limited to erythrocyte parameters, including red blood cell count, hemoglobin, and hematocrit, emerging after puberty; sex partitioning was unnecessary for most analytes. Application of the Vietnamese vs. CALIPER reference intervals in an outpatient cohort resulted in bidirectional reclassification, with 0.0–32.6 % of CALIPER-abnormal results reclassified as normal and 0.0–24.4 % of CALIPER-normal results reclassified as abnormal, depending on the analyte. Conclusions This study establishes population-based pediatric CBC RI for Vietnamese children. Non-local pediatric RI may alter abnormal flagging and result interpretation in routine practice.