Effect of calcium treatment on urinary stone index after intestinal bypass for obesity.

The urinary excretion of oxalate, calcium, magnesium and creatinine was investigated in 21 outpatients who underwent jejunoileal bypass operation 6-9 years previously. Furthermore, a urinary stone index expressed as the quotient (calcium X oxalate)/(magnesium X creatinine) (mmol/mol) was calculated. The oxalate excretion exceeded normal ranges in 20 patients (1.20 +/- 0.55 mmol/24 h), and the stone index was found critically high in all. Daily administration of 1,100 mg ionized calcium in 17 of these patients die not change the urinary excretion of oxalate, calcium and magnesium separately, but the stone index was reduced significantly suggesting some preventive effect of calcium on the tendency of stone formation after jejunoileal bypass.