Idiopathic hypercalciuria. Renal and absorptive subtypes in children
L. C. Hymes and B. L. Warshaw
Twelve children with urolithiasis or unexplained episodes of gross
hematuria, hypercalciuria, and normal serum calcium levels were examined
with an oral calcium loading test. Eight patients displayed elevated
fasting urinary calcium excretion, consistent with renal hypercalciuria;
four exhibited normal fasting calcium excretion, which increased
excessively with calcium loading, suggesting hyperabsorption of intestinal
calcium. Evidence of secondary hyperparathyroidism was detected in three
children with renal hypercalciuria on the basis of urinary cyclic adenosine
monophosphate (cAMP) excretion. Serum calcium concentrations obtained four
hours after loading increased significantly in children with renal
hypercalciuria and were directly correlated with fasting urinary calcium
excretion. Among patients with renal hypercalciuria, serum calcium level
was higher in patients with normal fasting cAMP excretion. These results
suggest that hyperabsorption of intestinal calcium occurs in renal
hypercalciuria and may account for the lower-than-predicted incidence of
secondary hyperparathyroidism in these patients. Idiopathic hypercalciuria
may arise from one fundamental metabolic disturbance with varying degrees
of expression, rather than from two separate pathogenic mechanisms.