Urinary calcium and sodium excretion in healthy children

We measured blood and 24 hour urine calcium, electrolytes and creatinine in 230 healthy children (85 boys and 145 girls) aged between 4 and 16 years. In a random group of them (130 children), calcium and creatinine were also measured in the second morning urine sample in a fasting state. In another random group of 106 children, urinary sodium excretion was also assessed; N one of the urinary calcium excretion indices followed a normal distribution so we expressed them as percentiles (95th and 97th percentiles for 24 hour s urinary calcium excretion were 5.089 and 5.820 mg/kg/24 h), There were no sex differences. One-way analysis of variance showed that the 24 hour and spot urine ratios alcium/creatinine (mg/mg) were significantly different fo r age groups at the p < 0.05 level Urinary sodium excretion followed a gaus sian distribution and was significantly higher in boys than in girls. Pears on's correlation coefficients between second morning and 24 hour urinary ca lcium excretion as mg/kg/24 h and as the ratio calcium/creatinine (mg/mg), were 0.724 and 0.720 respectively. We performed a contingency fable between 24 hour and second morning urinary calcium excretion with cut-off values c ommonly used today (4 mg/kg/24 h and 0.2 mg/mg) to assess: reliability of s econd morning urinary calcium excretion for the screening of hypercalciuria , and we obtained 0.588 sensitivity and 0.973 specificity. Because of that, we think that ratio calcium/creatinine greater than or equal to 0.2 mg/mg has a poor sensitivity to discover hypercalciurias when it is applied to th e whole child population.