Background: The colonic biopsy is the only reliable method for identification of microscopic colitis in patients with chronic diarrhea and normal endoscopic findings. Methods: The Clinical Outcomes Research Initiative national endoscopic database was analyzed to determine the rate at which colonic biopsy specimens were obtained in patients undergoing colonoscopy for the evaluation of diarrhea with no visible mucosal abnormality. Results: Between January 2000 and December 2003, 5565 unique adult patients underwent colonoscopy for evaluation of diarrhea without detection of any mucosal abnormality. Colonic mucosal biopsy specimens were obtained in 4410 (79.2%) of these patients. The rates at which biopsy specimens were obtained differed among the sites where colonoscopy was performed; biopsy specimens were obtained from more patients undergoing colonoscopy in university-affiliated settings (86.8%) compared with Veterans Affairs Medical Centers (VAMC) (78.5%) or community sites (78.6%) (p <0.001). On multivariate analysis, biopsy specimens were more likely to be obtained in younger patients (OR 0.7: 95%CI[0.6, 0.8] for age >50 years vs.
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