How is Crohn's disease diagnosed? Your doctor will ask you about your symptoms and do a physical exam. You may also have X-rays and lab tests to find out if you have Crohn's disease. It may go undiagnosed for years, because symptoms usually develop gradually and it doesn't always affect the same part of the intestine. Other diseases can have the same symptoms as Crohn's disease. But doctors can diagnose Crohn's by doing a test that looks at the inside of the intestine and doing a biopsy. Diagnostic tests Biopsy. This test is done on a sample of tissue collected during a colonoscopy. Bowel biopsies are painless (other than the possible discomfort of the scope procedure). They remove only a tiny piece of tissue. Colonoscopy or flexible sigmoidoscopy. Colonoscopy is often the preferred test because it can be used to examine the entire colon. Sigmoidoscopy reaches only the lowest part of the colon. Abdominal X-ray. This test can show possible obstructions in the belly. Upper gastrointestin...