The diagnosis of inflammatory bowel disease is suspected if the symptoms are persistent or recurrent.

Initially the common tests such as complete blood count (CBC), erythrocyte sedimentation rate (ESR), C-reactive protein and stool routine and culture are done. If stool test does not show common bacterial infection and symptoms persist after treatment, further investigations are pursued. A test called as stoo calprotectin may be useful in deciding whether further investigations are required These consist of sigmoidoscopy or colonoscopy. Sigmoidoscopy is visualization of rectumn and sigmoid colon. The inflammation and its severity can be diagnosed there is inflammation, biopsy (tissue sample) can be taken to view the tissue under microscope. Colonoscopy usually requires bowel preparation to clean the large intestine and it can visualize entire large intestine and few centimeters of adjacent small bowel. The colonoscopy and biopsy is used to decide the extent of ulcerative colitis and area affected in Crohn’s disease. The small intestine is very long and cannot be visualized by the usual endoscopy. Hence to diagnose the small intestinal involvement, CT scan and/or MRI tests are required.

Other tests are asked for specific purposes- an upper gastrointestinal endoscopy. capsule endoscopy or endoscopy of small bowel (enteroscopy) etc especially in Crohn’s disease.