Urinary patterns of patients with renal stones associated with chronic inflammatory bowel disease.

OBJECTIVE: The aim of this study was to analyze the frequency of renal stone patients with chronic inflammatory bowel disease and their urinary patterns.
METHODS: During a 20-year period, 1941 consecutive patients with renal stone disease underwent routine laboratory procedures including a fasting blood sample for chemistry profile and a 24-hour urine collection for analyses of electrolytes. Thorough histories including chronic inflammatory disease or ileal resection were obtained. Patients with inflammatory bowel disease together with a control group comprising 47 idiopathic renal calcium stone formers were submitted to a xylose absorption test for evaluation of intestinal absorption.
RESULTS: We observed 10 patients with Crohn's disease, 12 with ulcerative colitis and one patient with ileal bypass for obesity. Six patients underwent ileal resection and 10 patients total colectomy. Urinary oxalate excretion was significantly higher and urinary citrate lower in stone patients with ileal disease (Ox 60 +/- 23, Cit 113 + 7-118 mg/day) than in idiopathic stone formers (Ox 28.2 +/- 11.5, Cit 381 +/- 205) and stone patients with ulcerative colitis (Ox 20.3 +/- 14.8, Cit 369 +/- 247). Urinary volume was significantly lower in patients with ulcerative colitis. A significant inverse correlation (-0.38, p < 0.01) between oxalate urinary excretion and blood xylose level was found 2 hours after ingestion of xylose. No significant reduction of xylose absorption was demonstrated in both normoxaluric and hyperoxaluric idiopathic stone patients.
CONCLUSIONS: Crohn's disease and ulcerative colitis are characterized by recurrent inflammatory involvement of different intestinal segments involving distinctive urinary patterns. Malabosorption associated with ileal disease causes increased oxalate absorption by increasing oxalate solubility in the intestinal lumen and permeability of the colonic mucosa; a reduced citrate excretion is associated in relation to mild acidosis due to the loss of bicarbonate in the liquid stool. In ulcerative colitis, especially if an ileostomy is present, urine are scanty and concentrated, and urine pH falls, leading to uric acid or mixed stones. Mild hyperoxaluria of idiopathic renal stone formers is not related to subtle intestinal malabsorption.