Effects of Weight and Glucose Ingestion on Urinary Calcium and Phosphate Excretion: Implications for Calcium Urolithiasis

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Abstract
Renal handling of phosphate and calcium was studied in 17 hypercalciuric stone-formers, 6 normocalciuric stone-formers and 10 normal subjects before (fasting state) and 45 and 75 min after the ingestion of 100 g glucose. The ratio of fasting urinary calcium to creatinine (Uca/creat) was higher in hypercalciuric than in normocalciuric stone-formers or controls. A positive correlation was found between weight index and fasting Uca/creat for all subjects studied (r = 0.36; P < 0.05). A negative correlation was apparent between the weight index and the fasting renal threshold phosphate concentration (TmP/ GFR) (r = 0.40; P < 0.02), the latter parameter being slightly but insignificantly lower in hypercalciuric stone-formers than in controls. After glucose ingestion, Uca/creat rose significantly in all groups. The maximal rise in Uca/creat was also positively correlated with the weight index for all patients (r = 0.42; P < 0.02), and 75 min after glucose ingestion, TmP/GFR decreased in all groups, dropping to a significantly lower level in the hypercalciuric patients than in the controls. No correlation was apparent between the weight index and the magnitude of the reduction in TmP/GFR. Plasma 1, 25−dihydroxyvitamin D3 and immunoreactive parathyroid hormone were measured before glucose ingestion and were not correlated either with each other or with plasma phosphorus, TmP/GFR, or Uca/creat before or after glucose ingestion. These results imply that weight is a determining factor in the renal handling of calcium and phosphorus. Such findings might be of importance to the clinical investigation and management of calcium stone-formers. (J Clin Endocrinol Metab54: 1063, 1982)

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