INFLUENCE OF CALCIUM INTAKE ON CALCITRIOL LEVELS IN IDIOPATHIC HYPERCALCIURIA IN CHILDREN

Twenty-four children with idiopathic absorptive hypercalciuria (IAH) a nd a control group (CG) of 11 healthy children were studied. Plasma 1, 25-hydroxyvitamin D3 (calcitriol), parathyroid hormone (PTH), calcium (Ca) and phosphate (P) levels were measured during dietary manipulatio n. The three diets analized were: (A) calcium-restrictive diet (400 mg /1.73 m2/day) for 7 days; (B) supplemented diet (1,000 mg/1.73 m2/day) for 3 days; (C) supplemented diet continued for 15 days. The IAH grou p had higher levels of serum calcitriol than the control group for all three diets. Serum calcitriol levels in the IAH group decreased in di et B compared to diet A, and returned to levels observed with diet A d uring diet C. Serum Ca, P and plasma PTH levels did not vary throughou t the study in either group. In IAH, two subgroups were observed. In o ne, serum calcitriol levels were elevated and in the other, serum calc itriol levels were not different from the controls. This second group had a lower P and maximum rate of tubular reabsorption of phosphate pe r 100 ml of glomerular filtrate than the IAH group with elevated serum calcitriol levels and the control group. These results suggest that I AH in children may be related both to increased serum calcitriol level s and to an altered Tmp/GFR.