Hypocalcemic Hypercalciuria During Vitamin D and Dihydrotachysterol Therapy of Hypoparathyroidism*†

Hypocalcemic hypercalciuria during vitamin D and dihydrotachysterol therapy is reported in 10 patients with postoperative and idiopathic hypoparathyroidism. This phenomenon was not observed in 6 patients with pseudohypoparathyroidism. A direct effect of vitamin D and dihydrotachystcrol in decreasing tubular reabsorption of calcium is the most likely cause of such hypercalciuria and may represent a fourth action of vitamin D. In view of the common occurrence of hypocalcemic hypercalciuria, the presence of calcium in the urine (Sulkowitch test) cannot be regarded as a reliable guide to the therapy of hypoparathyroidism.