If your healthcare provider suspects that you have efferent loop syndrome as a result of a gastric bypass procedure, he or she may perform a physical exam, upper gastrointestinal X-ray, or a CT scan to look for the blockage. Healthcare providers will use an endoscope, a thin, lighted tube with a tiny camera at the end, passed through your mouth and into your intestines to confirm the diagnosis. In some cases, where the clinical suspicion is high, additional testing is not needed. The diagnosis is confirmed at the surgery.