What is the best next step for a 30-year-old man with worsening abdominal pain and bloody diarrhea due to noncompliance with ulcerative colitis treatment?

In the scenario where a 30-year-old man with ulcerative colitis is experiencing worsening abdominal pain and bloody diarrhea, the best next step is to perform a plain abdominal X-ray. This imaging technique is particularly valuable in assessing potential complications such as colonic dilation, which can occur in the context of ulcerative colitis, especially with noncompliance to treatment.

The presentation of worsening symptoms suggests a possibility of complications like toxic megacolon or perforation, which may require urgent intervention. A plain abdominal X-ray can quickly evaluate these concerns by providing a view of the colon and identifying abnormal distention or air-fluid levels that could indicate a serious complication.

In contrast, while colonoscopy is a crucial tool for visualizing the intestinal mucosa and can help assess the severity of ulcerative colitis, it is less useful in acute settings without prior imaging to rule out complications that may preclude the procedure safely. Similarly, a CT scan of the abdomen, although helpful in diagnosing complications, involves more radiation exposure and may be less readily available in some urgent care settings compared to the quick and bedside assessment provided by plain X-rays. Lastly, stool culture is more relevant in cases of infectious diarrhea, which is not the primary concern here given the patient's known