What tests do doctors use to diagnose ulcerative colitis? Doctors may use blood tests, stool tests, and endoscopy of the large intestine to diagnose ulcerative colitis. Blood tests. A health care professional will take a blood sample from you and send the sample to a lab. Doctors use blood tests to check for signs of ulcerative colitis and , An ulcerative colitis diagnosis is based on several factors, including your medical history, a physical exam, and a series of medical tests. The tests your doctor recommends will help your healthcare team determine if you have ulcerative colitis and which type of ulcerative colitis you have. Initial Testing and Evaluation, Diagnosis of Ulcerative Colitis Clinical, Laboratory, and Radiographic Diagnosis. Clinical, laboratory, endoscopic, and histopathologic information are used to establish a diagnosis of ulcerative colitis (UC), one of the two main subtypes of inflammatory bowel disease (IBD), along with Crohn's disease (CD)., , , .