Study of Urinary Calcium Excretion after Oral Calcium Load in Stone Formers, Their Spouses and First-Degree Blood Relatives

Abstract

Hypercalciuria has long been considered a common abnormality in stone formers, and familial predisposition to renal stone formation has also been reported. Renal stone formers, their spouses and first-degree blood relatives (the latter two groups of subjects had no previous or present history of stone disease) were investigated for their response to an oral load of 2 g calcium (as di-calcium phosphate). Serum calcium, phosphorus, uric acid, creatinine and urea were within the normal range in all the subjects initially as well as 4 h after the load. After the oral calcium load, 66.6% of the stone formers, 25% of the first-degree relatives and none of the spouses were hypercalciuric. Administration of 2 g calcium produced a significantly greater urinary excretion of calcium in stone formers (123.8 +/- 43 mg/8 h, p < 0.001) and their first-degree blood relatives (89.8 +/- 26 mg/8 h, p < 0.01) as compared to the spouses of stone formers (65.5 +/- 12.8 mg/8 h). A significant increase in urinary calcium excretion after calcium loading was also found among the stone formers (p < 0.01) as compared to their first-degree blood relatives. A significantly higher mean rise in calcium excretion (over the basal excretion) in calcium stone formers (p < 0.001) and their first-degree blood relatives (p < 0.01), as compared to the spouses of stone formers suggests a greater predisposition to renal stone disease in first-degree blood relatives than the spouses of the stone patients.