Which diagnostic test is commonly used to establish a diagnosis of ulcerative colitis?

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Diagnosing ulcerative colitis relies on directly inspecting the colon lining and confirming inflammatory changes with tissue samples. Flexible sigmoidoscopy allows you to visualize the mucosa of the rectum and distal colon, where UC usually begins, and to take biopsies for histology. This combination—visual evidence of continuous mucosal inflammation and supportive biopsy findings (such as crypt distortion and chronic inflammatory infiltrates)—helps establish the diagnosis and distinguishes UC from other conditions like Crohn’s disease.

Other tests listed aren’t used to establish UC. Abdominal X-ray can show complications (for example, toxic megacolon) but not the diagnostic features of UC. EEG is a brain test and has no role in bowel disease, and chest X-ray assesses thoracic issues, not colonic inflammation.