How is ulcerative colitis diagnosed?
The most accurate way to diagnose ulcerative colitis is by examining the colon with a fiber-optic endoscope inserted into the rectum. A
sigmoidoscopy examines the lower third of the colon and requires minimal preparation. A
colonoscopy examines the full colon and requires a thorough bowel cleansing to ensure complete visualization of the lining of the colon. When ulcerative colitis is present, the lining of the colon appears swollen and inflamed, with surface bleeding and ulcers (if severe enough) usually in a continuous pattern. Tiny samples (biopsies) of the lining of the colon are taken during the procedure, so that a pathologist may examine them under the microscope for inflammatory changes (histology). This combination of endoscopy and histology is the gold standard for diagnosis of ulcerative colitis. Nevertheless, in patients with signs of severe colitis, (a colonoscopy may be postponed, as the lining of the colon becomes very fragile and easy to damage with the endoscope, but a sigmoidoscopy would be done to assess the state of the disease).
Abdominal CT scans can detect thickening of the colonic lining, and identify the extent of involvement of the colon, but cannot distinguish between ulcerative colitis and other types of colitis (see above).
Examination of the stool under the microscope is important to exclude infections of the colon that can cause similar symptoms to ulcerative colitis. Even patients known to have ulcerative colitis can acquire these infections and develop worsening symptoms. Recognizing these infections is important, as the treatment for ulcerative colitis could worsen the infectious process.
In patients with diarrhea and abdominal pain, clues to the presence of ulcerative colitis in laboratory blood tests would include anemia (low Hemoglobin/Hgb and Hematocrit/HCT) and an elevation of inflammatory markers, Erythrocyte Sedimentation Rate (ESR) or C-Reactive Protein (CRP).