What kind of complications might happen from a sigmoidoscopy?

Safe sigmoidoscopy. Sigmoidoscopy, when performed by a trained & experienced endoscopist is generally safe. However, risks to consider, as with any endoscopic test include: tears in the lining of the gut, perforation of the gut that may require surgery to fix, bleeding that may need transfusion, adverse reaction to sedation, infection, a missed diagnosis, and an incomplete test due to patient factors.