Twenty-four-hour Profiles of Urinary Excretion of Calcium, Magnesium, Phosphorus, Urea, and Creatinine in Healthy Prepubertal Boys

Objectives: Available data on 24-h urinary solute excretion in healthy children are sparse. We thus documented the daily and overnight variations of urinary electrolytes (calcium, magnesium, and phosphorus), urea, and creatinine in prepubertal (Tanner stage I) boys.

Design And Methods: Nine voluntary healthy prepubertal boys aged 10.8+/-0.11 years participated in this study. Concentrations of variables were quantified in daytime samples (collected between 07:00 h+/-30 min and 21:00 h+/-30 min) and nighttime samples (collected between 21:00 h+/-30 min and 07:00 h+/-30 min) in spring, during a period of 24-h every 3 h.

Results: Significant differences were found between daytime and nighttime excretion of calcium (p<0.05), magnesium (p<0.001), phosphorus (p<0.01), and urea (p<0.05), with high concentrations during the night. The 24-h solute/creatinine ratio was 0.072+/-0.008 mg/mg for calcium, 0.069+/-0.008 mg/mg for magnesium, 0.698+/-0.070 mg/mg for phosphorus, and 0.017+/-0.001 g/mg for urea. Statistically significant correlation analyses showed that urea and creatinine were positively associated with body mass index (BMI) (R=0.790, p=0.0113 for urea; R=0.889, p=<0.0013 for creatinine) and weight (R=0.717, p=0.0297 for urea; R=0.978, p=<0.001 for creatinine). The other urinary variables were independent of BMI and body mass.

Conclusion: These data are of interest for the diagnosis of certain renal disease in prepubertal children.