Background and aimPediatricians commonly use the complete blood count (CBC) of capillary blood to evaluate health status, guide diagnoses, and determine treatment strategies. This study aimed to establish sex- and age-specific reference intervals (RIs) for 23 capillary CBC parameters for urban preschoolers in Fuzhou, Southeast China. Materials and MethodsCapillary blood CBC data of 18,369 healthy preschoolers who underwent annual physical examinations at Fujian Maternity and Child Health Hospital between January 01, 2022, and November 31, 2023, were analyzed retrospectively. To fully validate the new RIs, the data of all apparently healthy children within the same age cohort at the same institution were comprehensively analyzed in December 2023. The new RIs were assessed by comparing them with the RIs currently used in laboratories and those obtained from different regions, sample types, or methodologies. ResultsDynamic temporal changes that differ between males and females were observed in the blood system of 3-7-year-old children in this region. The new sex- and age-specific RIs for capillary CBC parameters were feasible to guide clinical decision-making in the local region. ConclusionsOur findings demonstrated the importance of establishing sex- and age-specific RIs for each region and underscored the necessity of continuous adjustment of clinical Rls based on statistical rules and clinical responses.