What is the test of choice for evaluating suspected small bowel obstruction?

The test of choice for evaluating suspected small bowel obstruction is the upright abdominal series. This series typically includes both upright and supine X-rays of the abdomen, which are helpful in identifying the presence of air-fluid levels, enlarged loops of bowel, and other indicators of obstruction.

In a patient with a small bowel obstruction, the upright view is particularly useful because it allows the visualization of air-fluid levels that form when fluid and air accumulate above the area of obstruction. Often, these air-fluid levels are seen as distinct horizontal lines in the small intestine, and the presence of multiple air-fluid levels suggests a more distal obstruction. Additionally, the upright abdominal series is a fast, non-invasive initial study that can quickly elucidate the presence of an obstruction, making it an appropriate choice in such clinical scenarios.

Endoscopic examination is generally not utilized for diagnosing small bowel obstruction since it is more invasive and is not the best initial approach. X-ray only lacks the additional context provided by the upright series and would not capture the specific signs of obstruction effectively. Urinalysis is irrelevant in diagnosing gastrointestinal obstructions and provides no diagnostic information regarding the bowel itself. Thus, the upright abdominal series is the preferred method to evaluate suspected small bowel obstruction.