The diagnosis of Crohn’s disease or ulcerative colitis is sometimes delayed as the same symptoms can occur with other diseases. It is usually necessary to exclude diseases such as bowel infections or irritable bowel syndrome.
Blood tests are useful to look for anaemia (low blood count) and to measure the severity of inflammation. They can also detect vitamin or mineral deficiencies. A faeces (bowel motion) specimen may be required to exclude infection.
Most people require an examination of part of the bowel, either by direct inspection through a flexible tube inserted through the back passage (colonoscopy or sigmoidoscopy) or mouth (gastroscopy), or by x-rays, include CT scan and barium small bowel series (where dye is swallowed and x-rays taken). There is no one test that can reliably diagnose all cases of IBD, and many people require a number of tests.
Crohn’s disease is suspected in people who have been experiencing symptoms such as abdominal pain, diarrhoea and weight loss that have lasted for weeks or months. Because there is no single test that can establish the diagnosis of Crohn’s disease with certainty, and because Crohn’s disease often mimics other conditions, it may take time and several investigations to arrive at the correct diagnosis.
Whenever a person has a history of bleeding from the rectum – either with or without diarrhoea and abdominal pain – one of the conditions suspected as a possible cause of the symptoms is ulcerative colitis. Investigations are then carried out to differentiate between other diseases known to cause rectal bleeding (e.g. Crohn’s disease or colorectal cancer) and to arrive at what is called a ‘definitive diagnosis’.
Sometimes patients present with feature of both ulcerative colitis and Crohn’s disease and it is impossible to distinguish between the conditions. In this case they will receive a diagnosis of IBD unclassified (IBDU – previously known as indeterminate colitis). About 10-15 per cent of people diagnosed with inflammatory bowel disease are initially given a diagnosis of IBDU. Although ulcerative colitis and Crohn’s disease share some similarities, there are some important differences which help doctors identify the most appropriate treatment for each condition.