Urinary excretion of calcium following an oral calcium loading test in healthy children.

The ratio of urinary calcium (UCa)/urinary creatinine (UCr) concentrations (mg/mg) during calcium loading has been used to diagnose hypercalciuric states in adults. The UCa/UCr ratios have been examined before and after an oral dose of calcium in 48 healthy children following five days of abstinence from dietary milk products. No differences in UCa/UCr ratios were observed between sexes, races, or age groups. UCa/UCr ratio before the calcium dose was 0.09 +/- 0.12 (mean +/- 2 SD) and increased to 0.12 +/- 0.15 in urine samples collected for four hours after the calcium load. A direct relationship between UCa/UCr ratio and urinary sodium (UNa)/UCr ratio was observed (r = .57, P less than .01). In six children, calcium loading studies were repeated without prior restriction of dietary calcium. Dietary calcium intake before the calcium loading had little effect upon UCa/UCr ratio before the calcium in these six children (0.068 vs 0.08); however, UCa/UCr values after the calcium load were significantly lower (0.08 vs 0.15) when no dietary calcium restriction preceded the calcium-loading study. These data may allow characterization of renal hypercalciuria and gastrointestinal hyperabsorption of calcium in children with urolithiasis.