Urinary calcium excretion in healthy adolescents

To establish normative data for urinary calcium excretion in healthy adolescents, we measured calcium-creatinine ratios (UCa/Cr) in urine samples collected from 222 middle school teenagers of diverse racial and socioeconomic backgrounds. Median UCa/Cr were: white girls, 0.23 mmol/L per mmol/L (0.08 as mg/dl per mg/dl); black girls, 0.14 (0.05); white boys, 0.14 (0.05); and black boys, 0.08 (0.03). The 95th percentile values for UCa/Cr were: white girls, 0.54 (0.19); black girls, 0.59 (0.21); white boys, 0.68 (0.24); and black boys, 0.50 (0.18). By nonparametric analysis, girls had significantly higher UCa/Cr than boys (p less than 0.01), and whites had significantly higher urinary UCa/Cr than blacks (p less than 0.01). No significant correlation was found between Tanner stage and UCa/Cr in either sex. This study provides data for detecting adolescents with high urine calcium excretion, which should be useful clinically and in studies designed to evaluate the significance of persistent hypercalciuria.