Diagnosis of Ulcerative Colitis Introduction Ulcerative colitis is the chronic inflammation of the innermost lining of the large intestine (colon). It ranges from mild to severe. Causes of Ulcerative Colitis The specific cause of ulcerative colitis is not known, but the probable cause of UC is improper functioning of the immune system. The other factors that may cause ulcerative colitis are hereditary, age and environmental factors. Signs and Symptoms of Ulcerative Colitis Blood & mucus in stools Diarrhea Abdominal pain Rectal pain Fatigue Increased abdominal sounds Gas formation Weight loss Lack of appetite Fever