Crohn's diseases or colitis share many symptoms with other common conditions, such as irritable bowel syndrome, gastroenteritis and coeliac disease. Your doctor will usually examine you and take a detailed history of your symptoms to help rule out these other diseases.

There is no single test that can be used to confirm the diagnosis of Crohn's disease or colitis. A combination of the following tests is usually needed:

• Blood tests can help to rule out other medical conditions, and certain markers in the blood can indicate that inflammation is present.
• A stool sample may be examined to check for other possible causes of diarrhoea and inflammation, such as infections.
• A colonoscopy or flexible sigmoidoscopy may be performed, where a tiny camera is placed up the back passage and into the bowel so the lining can be checked for ulcers, inflammation and bleeding.
• Biopsies (small samples of tissue) may be taken from inside the bowel so a pathologist can examine the tissue under a microscope to look for signs of disease.
• Other types of imaging (such as x-ray) are sometimes used to help in the diagnosis and to help rule out other diseases.

Even with testing it can be difficult to distinguish between Crohn's disease and colitis. Because the medical management of these diseases depends more on the location and severity of disease, a precise diagnosis may not always be necessary for effective management to take place.

Sources: Digestive Health Foundation (Publication - Andrews JM, Sinclair M. Australian Guidelines for General Practitioners and Physicians. Inflammatory Bowel Disease, Third Edition, 2013.)