To diagnose ulcerative colitis, your GP will first ask about your symptoms, general health and medical history.
They'll also physically examine you, checking for signs such as paleness (caused by anaemia) and tenderness in your tummy (caused by inflammation).
A stool sample can be checked for signs of infection, as gastroenteritis (infection of the stomach and bowel) can sometimes have similar symptoms to ulcerative colitis.
Blood tests may also be carried out to check for anaemia and to see if there's inflammation on any part of your body.
If your GP suspects you may have inflammatory bowel disease (IBD) (a term mainly used to describe 2 diseases: ulcerative colitis or Crohn's disease), you may be referred to hospital for further tests.
A diagnosis of ulcerative colitis can be confirmed by examining the level and extent of bowel inflammation.
This is initially done by using a sigmoidoscope, a thin, flexible tube containing a camera that's inserted into your rectum (bottom).
A sigmoidoscopy can also be used to remove a small sample of tissue from your bowel so it can be tested in a laboratory. This is known as a biopsy.
The procedure can be uncomfortable and you can be given a sedative to help you relax.
It usually takes around 15 minutes and you can often go home the same day.
During this procedure, only the rectum and lower part of the colon are examined.
If it's thought your ulcerative colitis has affected more of your colon, another examination will be required. This is known as a colonoscopy.
A colonoscopy uses a flexible tube containing a camera called a colonoscope, which allows your entire colon to be examined. A biopsy sample can also be taken.
Before having a colonoscopy, your colon needs to be completely empty, so you'll need to take strong laxatives beforehand.
A colonoscopy can be uncomfortable, but you'll be given sedatives and pain medications to help you relax and make the procedure as painless as possible.
The procedure takes around half an hour and you'll be able to go home the same day.