You lie on your left side with your knees drawn up to your chest.
The doctor gently places a gloved and lubricated finger into your rectum to check for blockage and gently enlarge (dilate) the anus. This is called a digital rectal exam.
Next, the sigmoidoscope is placed through the anus. The scope is a flexible tube with a camera at its end. The scope is gently moved into your colon. Air is inserted into the colon to enlarge the area and help the doctor view the area better. The air may cause the urge to have a bowel movement or pass gas. Suction may be used to remove fluid or stool.
The doctor may take tissue samples with a tiny biopsy tool inserted through the scope. Heat (electrocautery) may be used to remove polyps. Photos of the inside of your colon may be taken.
Sigmoidoscopy using a rigid scope may be done to treat problems of the anus or rectum.
How to Prepare for the Test
Your bowel needs to be completely empty and clean for the exam. A problem in your large intestine that needs to be treated may be missed if your intestines are not cleaned out.
Your health care provider will give you the steps for cleansing your bowel. This is called bowel preparation. Steps may include using enemas, not eating solid foods for 2 or 3 days before the test, and taking laxatives. Follow instructions exactly. This ensures accurate results.
How the Test will Feel
During the exam you may feel:
Pressure during the digital rectal exam or when the scope is placed in your rectum
The need to have a bowel movement
Some bloating or cramping caused by the air or by stretching of the bowel by the sigmoidoscope
After the test, your body will pass the air that was put into your colon.
Children may be given medicine to make them sleep lightly (sedated) for this procedure.
Why the Test is Performed
Your doctor may recommend this test to look for the cause of:
Diarrhea, constipation, or other changes in bowel habits
There is a slight risk of bowel perforation (tearing a hole) and bleeding at the biopsy sites. The overall risk is very small.
Kimmey MB. Complications of gastrointestinal endoscopy. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease: Pathophysiology/Diagnosis/Management. 9th ed. Philadelphia, PA: Elsevier Saunders; 2010:chap 40.
National Comprehensive Cancer Network. NCCN Clinical Practice Guidelines in Oncology: Colorectal cancer screening. Version 1 .2014. Available at: www.nccn.org/professionals/physician_gls/pdf/colorectal_screening.pdf. Accessed November 20, 2014.
Jenifer K. Lehrer, MD, Department of Gastroenterology, Frankford-Torresdale Hospital, Aria Health System, Philadelphia, PA. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.