PD28-11 URINARY STONE RISK AFTER COLON SURGERY: THE INFLAMMATORY BOWEL DISEASE BIAS

Abstract

INTRODUCTION AND OBJECTIVES: Previous studies investigating urinary stone risk after colon surgery have demonstrated significant reductions in urinary pH, volume, citrate, and magnesium that correspond to an increased incidence of kidney stones. These studies, however, have consistently included patients with inflammatory bowel disease (IBD) which may bias their findings due to known urinary abnormalities present prior to surgery and differences in length of bowel removed compared to other types of colon surgery. This study aims to evaluate urinary stone risk after colon surgery in patients with and without IBD. METHODS: Retrospectively, baseline 24-hour urine samples of 21 kidney stone patients with a history of colon resections were evaluated from a data set of over 800 patients. Urinary chemistries of those who required colon surgery for IBD (9 patients) and non-IBD reasons (12 patients) were compared to each other and a control of 52 first-time stone formers without bowel disease. RESULTS: The IBD colectomy group had a significantly lower urinary pH (5.55 vs 6.08, P1⁄40.003), magnesium (41.8mg/d vs 103.7mg/d, P1⁄40.0002), citrate (109.8mg/d vs 230.4mg/d, P1⁄40.0001), sodium (95.2mmol/d vs 177.9mmol/d, P1⁄40.013), and calcium (109.8mg/d vs 230mg/d, P1⁄40.01) than the control. The non-IBD colectomy group had lower pH (5.69 vs 6.09, P1⁄40.015) and higher supersaturation of uric acid (1.62 vs 0.87, P1⁄40.015) compared to the control. The IBD colectomy group revealed a lower magnesium (P1⁄40.04), citrate (P1⁄40.007), and sodium (P1⁄40.045) than the non-IBD colectomy group. 66% of the colectomies in the IBD group were total while 100% of the colectomies in the non-IBD group were partial. CONCLUSIONS: The urinary stone risk of colectomy patients with IBD is significantly different from colectomy patients without IBD and is more reflective of abnormalities present in IBD patients prior to surgery such as low citrate, magnesium, and urinary pH. It is likely the IBD patients biased the findings of previous studies investigating the urinary stone risk after colon surgery. Patients who underwent colon surgery for non-IBD reasons, however, have few urinary abnormalities and a urinary risk more similar to first-time stone formers. The difference in urinary risk of colectomy patients with and without IBD may be explained by the intrinsic stone risk present in IBD and the differences in length of bowel removed.