Development of a Score to Predict Positive Colonic Histology in Chronic Diarrhea Assessed in Open-access Colonoscopy

Goals: To evaluate the diagnostic yield of colonoscopy and esophagogastroduodenoscopy with biopsies and to identify predictors of positive colonic histology in patients with chronic diarrhea. Background: Colonoscopy with biopsies is performed in chronic diarrhea with negative initial work-up. Study: We reviewed electronic medical records of 1022 consecutive patients with chronic diarrhea referred for a first colonoscopy (including 25% open-access referrals). Predictors of positive colonic histology were investigated using logistic regression. Results: Four hundred thirteen patients with macroscopically normal colon were divided into derivation (n=275) and validation (n=138) cohorts. All patients underwent colonoscopy; 369 had ileoscopy (biopsies in 43%), and 289 underwent esophagogastroduodenoscopy (duodenal biopsies in 93%). In patients with endoscopically normal colon, histology was positive in 13.3%: 10.6% microscopic colitis; 1.5% other colitides. Among 358 patients with negative histology, the recorded diagnoses were: 48% unexplained, 25% irritable bowel syndrome, 5.6% small intestinal bacterial overgrowth, and 4.7% bile acid diarrhea. The rates of diagnoses based on positive histologies were 4% for ileal and 5% for duodenal biopsies. Older age [odds ratio (OR)=1.05] was a positive predictor, whereas body mass index (OR=0.93) and duration of diarrhea (OR=0.98) were negative predictors of positive histology. A clinical diagnostic scoring system could correctly predict 41% to 54% of patients with normal colonic histology, with a false-negative rate of 0.8% to 2.6% and a negative predictive value of 95% to 98%. Conclusions: Positive colonic biopsies were detected in <15% of patients with chronic diarrhea with normal colonoscopy; a clinical score correctly predicts likelihood of normal histology in about half the patients.