Establishing Biological Reference Intervals From 2 Million Routine Hospital Laboratory Results of 59,141 Patients Using an Indirect Method: Evidence From Adult and Pediatric Moroccan Populations

Objective: Establishing reference intervals (RIs) using direct sampling is costly and particularly challenging in pediatric populations.Moreover, RIs derived from Western populations may not be fully applicable to the Moroccan population.This study aimed to establish indirect RIs for 26 biochemical analytes in adults and children, with stratification by sex and age.Methods: We retrospectively analyzed 2,563,513 laboratory results between January 1, 2022, and August 7, 2024.After cleaning, 1,972,082 results from 59,141 patients were retained, and only the earliest result per patient and analyte was used for estimation.Pathological values were handled statistically by modelling the main distribution peak: RIs were estimated using Box-Cox transformation and peak modelling.Each RI covered the central 95% of the modeled non-pathological distribution, and its limits were given with 90% bootstrap confidence intervals (CIs).Results: RIs were successfully established for nearly all age and sex groups; several implausible pediatric limits were withheld.Several expected biological patterns were observed, including higher creatinine, uric acid, and gamma-glutamyl transferase (GGT) concentrations in men; higher alkaline phosphatase and phosphorus levels in younger children; increasing creatinine concentrations with age; and higher GGT and bilirubin levels in infants.Overall agreement with existing RIs was good for transaminases, alkaline phosphatase, urea, and creatinine.In contrast, shifts were observed in sodium, calcium, albumin, glucose, glycated hemoglobin (HbA1c), uric acid, GGT and lactate dehydrogenase (LDH) limits, which may be related to the hospital based population included in the study.Conclusion: Indirect estimation using large-scale routine laboratory data provided plausible and costeffective RIs for both adults and children in the Moroccan population.These findings may complement direct RI studies and provide a useful basis for local laboratory practice, although further validation in representative healthy populations remains necessary.