The Hypercalciurias CAUSES, PARATHYROID FUNCTIONS, AND DIAGNOSTIC CRITERIA

Abstract

A B S T R A C T The causes for the hypercalciuria and diagnostic criteria for the various forms of hypercal- ciuria were sought in 56 patients with hypercalcemia or nephrolithiasis (Ca stones), by a careful assessment of parathyroid function and calcium metabolism. A study protocol for the evaluation of hypercalciuria, based on a constant liquid synthetic diet, was developed. In 26 cases of primary hyperparathyroidism, characteristic features were: hypercalcemia, high urinary cyclic AMP (cAMP, 8.58+3.63 SD gmol/g creatinine; normal, 4.020.70 umol/g creatinine), high immunoreactive serum parathyroid hormone (PTH), hypercalciuria, the urinary Ca exceeding absorbed Ca from intestinal tract (CaA), high fasting urinary Ca (0.2 mg/mg creatinine or greater), and low bone density by 'I photon absorp- tion. The results suggest that hypercalciuria is partly secondary to an excessive skeletal resorption (resorptive hypercalciuria). The 22 cases with renal stones had normocalcemia, hypercalciuria, intestinal hyperabsorp- tion of calcium, normal or low serum PTH and urinary cAMP, normal fasting urinary Ca, and normal bone density. Since their CaA exceeded urinary Ca, the hyper- calciuria probably resulted from an intestinal hyper- absorption of Ca (absorptive hypercalciuria). The pri- macy of intestinal Ca hyperabsorption was confirmed by responses to Ca load and deprivation under a me- tabolic dietary regimen. During a Ca load of 1,700 mg/day, there was an exaggerated increase in the renal excretion.of Ca and a suppression of cAMP excre- tion. The urinary Ca of 453+154 SD mg/day was sig- nificantly higher than the control group's 211+42 mg/ day. The urinary cAMP of 2.260.56 umol/g creatinine was significantly lower than in the control group. In contrast, when the intestinal absorption of calcium was limited by cellulose phosphate, the hvpercalciuria was kc'ceiz(l for plblicatifn 9 July 1073 and in rezxsed form 11 September 1973. corrected and the suppressed renal excretion of cAMP returned towards normal. Two cases with renal stones had normocalcemia, hypercalciuria, and high urinary cAMP or serum PTH. Since CaA was less than urinary Ca, the hypercalciuria may have been secondary to an impaired renal tubular reabsorption of Ca (renal hypercalciuria). Six cases with renal stones had normal values of serum Ca, urinary Ca, urinary cAMP, and serum PTH (normocalciuric nephrolithiasis). Their CaA exceeded urinal Ca, and fasting urinary Ca and bone density were normal. The results support the pro- posed mechanisms for the hypercalciuria and provide reliable diagnostic criteria for the various forms of hypercalciuria.