Tubular reabsorption of calcium in normal and hypercalciuric subjects.

Tubular reabsorption and excretion of calcium were studied at different levels of filtered calcium by means of calcium infusion in normal and hypercalciuric subjects and in patients with idiopathic nephrolithiasis. Calcium reabsorption and excretion rose linearly with filtered load and in no case was a maximum tubular reabsorptive capacity for calcium reached. No decrease in tubular reabsorption of calcium was found in hypercalciuric as compared with normocalciuric subjects, and no difference in tubular reabsorption was found between patients with idiopathic nephrolithiasis and normal subjects. Calcium excretion and reabsorption calculated from the endogenous creatinine clearance during calcium infusion were virtually identical with the corresponding values calculated from the inulin clearance.