Urinary calcium was determined at two known levels of intake in 31 male and 21 female idiopathic stone-formers, and the results are compared with 13 males and 21 females with no history of stone. In addition, comparable data collected from the literature on 31 normal male adults are included. At low-calcium intakes there was little difference in the urinary calcium excretion of stone-forming and non-stoneforming individuals, but as the intake was raised the urinary calcium rose more steeply in the stone-formers than in the controls. “Hypercalciuria” was therefore detectable only at moderately high calcium intakes, the characteristic feature of this syndrome being a steep slope of urinary on dietary calcium. This relation of urinary to dietary calcium is similar to that reported by Knapp (1947) in a small proportion of normal individuals. It is concluded that “hypercalciuria” can only be defined in relation to calcium intake; that “idiopathic hypercalciuria” is generally attributable to an increased calcium absorption; and that the hypercalciuria of idiopathic stone disease is probably of the same nature as that seen in a small proportion of normal individuals.
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