Urinary Excretion of Calcium Following an Oral Calcium Loading Test in Healthy Children

Abstract

The ratio of urinary calcium (U_Ca)/urinary creatinine (U_Cr) concentrations (mg/mg) during calcium loading has been used to diagnose hypercalciuric states in adults. The U_Ca/U_Cr 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 U_Ca/U_Cr ratios were observed between sexes, races, or age groups. U_Ca/U_Cr 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 U_Ca/U_Cr ratio and urinary sodium (U_Na)/U_Cr ratio was observed (r = .57, P < .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 U_Ca/U_Cr ratio before the calcium dose in these six children (0.068 vs 0.08); however, U_Ca/U_Cr 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.