Anthropometry-based reference values for 24-h urinary creatinine excretion during growth and their use in endocrine and nutritional research

Background: Urinary creatinine reference values that take anthropometric data into account, which is mandatory during growth, are not available for healthy white children. Objective: We sought to establish anthropometry-based reference values for 24-h urinary creatinine excretion in healthy white children aged 3-18 y. Design: Anthropometric variables and 24-h urinary creatinine excretion rates were determined cross-sectionally (225 boys and 229 girls). Age and sex dependency of 24-h creatinine excretion (crude and related to individual anthropometric variables) were assessed to derive appropriate creatinine reference values. The applicability of these creatinine reference values for estimation of daily excretion of certain analytes was assessed in 40 additional children. Results: Sex-specific, body-weight-related creatinine reference values were derived fur the following age groups: 3, 4-5, 6-8, 9-13, and 14-18 y. The 5th percentile exceeded 0.1 mmol . kg(-1) . d(-1) in all age group, >3 y. The use of these creatinine reference values for estimating average 24-h excretion rates of certain analytes (determined as the ratio of analyte to creatinine in spot urine samples) yielded reasonable estimates of mean 24-h urinary excretion rates actually analyzed (spot and 24-h urine samples from the same children). Ideal 24-h creatinine excretion values for height were also derived for a potential determination of the creatinine height index. Conclusions: Established anthropometry-based creatinine reference values are recommended as a convenient, simple tool to 1) identify severe 24-h urine collection errors, 2) calculate average 24-h excretion rates of certain analytes from respective ratios of analyte to creatinine) determined in spot urine samples, and 3) assess somatic protein status by determining the creatinine height index.