LMS-based pediatric reference values for parameters of phosphate homeostasis in the HARP cohort

Supplemental Material zu folgender Publikation (Abstract) Context: The assessment of phosphate homeostasis in children is challenging due the marked changes in laboratory parameters during growth and development, and the lack of adequate reference values. Objective: To develop Lambda-Mu-Sigma (LMS)-based continuous pediatric reference percentiles for 7 key laboratory parameters of phosphate homeostasis. Design: Cross-sectional single center study: HAnnover Reference values for Pediatrics (HARP) study. Setting: Hospital clinics and secondary school. Patients: Four hundred and fifty-five children aged 0.1-18 years (254 boys). Main outcome measures: LMS-based continuous reference percentiles for serum phosphate, plasma intact fibroblast growth factor 23 (iFGF23), and its cofactor soluble Klotho (sKlotho), tubular maximum phosphate reabsorption per glomerular filtration rate (TmP/GFR), fractional tubular reabsorption of phosphate (TRP), and urinary calcium/creatinine (Ca/Crea) and phosphate/creatinine (Pi/Crea) ratios. Results: LMS-based percentiles and z-scores were established for 7 key laboratory parameters of phosphate homeostasis which were all found to be age-dependent. Serum phosphate, TmP/GFR and sKlotho associated with sex. Serum phosphate, TmP/GFR, and urine Ca/Crea and Pi/Crea levels are highest in infancy and decline until age 18 years, while phosphate and TmP/GFR values reached adult levels earlier in girls compared to boys. iFGF23 concentrations are highest in infancy and fall to a stable plateau by 4 years of age, while sKlotho peaks during adolescence. Conclusion: This is the first report of LMS-based continuous pediatric reference percentiles for key laboratory parameters of phosphate homeostasis that allow calculation of standardized patient z-scores to facilitate test result interpretation in children and adolescents.