Because of the potential relationship of increased urinary crystalloid excretion and concentration to stone formation, urinary calcium and uric acid excretion patterns were studied prospectively in 65 patients with inflammatory bowel disease and compared with excretion patterns in patients with functional bowel disease (controls) receiving similar dietary prescriptions.
Mean 24-hr urinary calcium excretion was higher in both ulcerative colitis (212 mg, p <0·02) and granulomatous bowel disease (168 mg, p = n.s.) than in controls (118 mg). Urinary calcium excretion exceeded 250 mg/24 hr in 11 of 34 patients with inflammatory bowel disease but in none of the controls. Eight of these 34 patients compared with one of 10 controls excreted urine with calcium concentrations greater than 20 mg/100 ml.
Mean 24-hr uric acid excretion was slightly higher in granulomatous bowel disease (520 mg) than in ulcerative colitis (450 mg) or functional bowel disease (451 mg). Eight patients with inflammatory bowel disease but no control subject excreted > 700 mg. The mean urinary uric acid concentration was significantly higher in ulcerative colitis (538 μg/ml, p <0·05) and granulomatous bowel disease (558 μg/ml, p <0·02) than in controls (338 μg/ml). The mean morning urine pH was lower (5·5, p <0·01) in ulcerative colitis than in the other groups.
These results indicate increased excretion and higher concentration of calcium and uric acid in some patients with inflammatory bowel disease on the usual treatment programmes. Only very long-term prospective studies of such patients can help to document the true contribution of increased crystalloid concentration and excretion to kidney stone formation in inflammatory bowel disease patients.
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