Diagnosis is done mainly from patient's history, clinical symptoms, sigmoidoscopy and biopsy.
Complete Blood count- Elevated levels of C-Reactive protein (CRP), Platelet count, erythrocyte sedimentation rate (ESR) and decrease in haemoglobin.
Stool examination- It is done to test for blood and is helpful to rule out bacterial or parasitic infections.
X-ray abdomen and barium enema- it is helpful in severe cases. Colonic thickening and toxic dilation can be seen on X-ray. Barium enema shows fine mucosal granularity in initial stages and thickened mucosa and superficial ulcers in severe disease.
Colonoscopy - Colonoscopy permits physician to view entire colon and take tissue sample (biopsy) for investigation.
Sigmoidoscopy- it is used to assess disease activity and extent of damage because of the disease.
Computed tomography (CT) Scan -it is of limited use in diagnosis. It is helpful in finding out complications from ulcerative colitis.