Investigations (tests) are necessary to reach the correct diagnosis and to check on the progress of the disease. After an initial examination in the clinic, some of the following tests may be performed:
1. Blood tests
• Full blood count (FBC) - to check for anaemia, and level of white cells & platelets.
• To check the proteins in the blood: A low level of albumin in the blood suggests severe ulceration. A raised 'C' reactive protein (CRP) reflects inflammation.
• Liver function tests (LFTs)- to check the condition of the liver.
• Urea and electrolytes (U&Es) to see if there is an imbalance of salt and water due to diarrhoea.

2. Stool tests
A relapse may be due to infection and this can be excluded by looking for bacteria in the stool.

3. Sigmoidoscopy
An examination of the lower bowel with a rigid metal tube that has a light on the end. Small pieces of tissue called biopsies may be taken for examination under the microscope.

4. Plain abdominal film
Straight x-ray of the abdomen may show swelling and obstruction of the bowel or constipation.

5. Barium x-rays
Barium Sulphate is a liquid, which shows up on x-ray and can therefore be used to demonstrate the bowel, which is otherwise poorly seen. It may be given by mouth to examine the small intestine or by enema to examine the large intestine.

6. Colonoscopy
An examination in which the large intestine (colon) is examined by a long, flexible, fibre optic (fibres which carry light) telescope called a colonoscope. Biopsies may be taken for examination under the microscope.

7. White cell scan (leukocyte scan)
A scan in which the patients' own white blood cells, labeled with a tiny amount of radioactivity, are used to show the extent and severity of inflammation.