Pathophysiologic studies in idiopathic hypercalciuria presenting in childhood.

Idiopathic hypercalciuria (IH) was diagnosed in 11 children aged 5 3/12 to 10 6/12. Eight patients investigated 1-12 years later still had hypercalciuria. When compared to a control group of 10 healthy children, 5 patients demonstrated an excessive rise in urinary Ca excretion following an oral Ca load. These patients also demonstrated low urinary cAMP, normal serum iPTH and high normal iTCT levels. The remaining 3 patients responded normally to Ca loading, but otherwise showed similar metabolic findings as the above group. These findings suggest a hyperabsorptive mechanism for all our patients. The finding of relatively low values for TmP/GFR in most IH patients further suggests that here, as in many adult patients, this may be the primary pathogenic mechanism, causing low serum P, increased synthesis of 1,25 dihydroxyvitamin D and, thus, absorption of Ca. We believe this represents a physiologic variant state and not a disease state.