In a patient with acute ulcerative colitis flare presenting with fever and LLQ pain, what is the BEST diagnostic test to order?

• A. Abdominal CT
• B. Sigmoidoscopy
• C. KUB
• D. Barium enema

Answer: (B)

The key idea is that confirming and characterizing an active ulcerative colitis flare relies on direct mucosal evaluation with biopsy. Flexible sigmoidoscopy lets you visualize the rectum and sigmoid colon—the regions UC typically involves first and continuously—and obtain biopsies for histology. This yields both visual evidence of inflammatory patterns (erythema, friability, superficial ulcerations) and tissue confirmation (crypt distortion, goblet cell depletion, crypt abscesses) that distinguish UC from infectious colitis and help gauge disease extent.

Compared with other tests, sigmoidoscopy provides diagnostic certainty with less risk than a full colonoscopy in an acutely inflamed colon. It avoids the higher perforation risk and the more invasive preparation required for a complete colonoscopy, and it’s more informative for diagnosis and extent than a plain X-ray (KUB) or a barium study, which don’t supply mucosal visualization or histology. Abdominal CT can help detect complications but isn’t diagnostic of UC itself, and a barium enema is generally avoided in active colitis due to perforation risk and potential to worsen inflammation.

So, flexible sigmoidoscopy with biopsy is the appropriate test to confirm disease and assess extent during an acute UC flare.