PRECISE DETERMINATION OF THE ABSORPTIVE COMPONENT OF URINARY CALCIUM EXCRETION USING STABLE ISOTOPES

Some patients with hypercalciuria are thought to have enhanced enteric calcium absorption, with a major component of recent diet contributin g to urinary calcium. This mechanism has been difficult to test with t he usual calcium loading procedures. We employed dual stable calcium i sotope tracers to quantitate the components of urinary calcium excreti on in 38 healthy female children. The mean urinary calcium excretion i n these girls was 2.4 mg/kg per day. The contribution of recent diet t o this total was a mean of 0.2 mg/kg per day. The maximum dietary cont ribution to urinary calcium excretion was 0.86 mg/kg per day. Recent d iet contributes a mean of 8% to total dietary calcium excretion. This novel method permits precise quantitation of the contributions of rece nt diet and tissue stores to urinary calcium excretion. In these healt hy girls, the fraction of urinary calcium derived from diet is trivial .