A flexible sigmoidoscopy explores the inside of the lower third of the colon to detect abnormalities. This 10-15-minute test is usually done as an outpatient procedure and requires the same advance preparation as a colonoscopy.

It is important to note that a flexible sigmoidoscopy is an effective screening test for only the rectum and lower part of the colon. The test does not examine the upper portion of the colon, where as many as 50% of cancerous and pre-cancerous polyps develop. As a result, a sigmoidoscopy is not considered a comprehensive screening for colorectal cancer.

This test is often performed without sedation in a physician's office. The sigmoidoscopy procedure itself generally takes 10 to 15 minutes to complete. While you are lying on your side, your physician will gently insert the narrow sigmoidoscope into the rectum and slowly up through the lower part of the colon. Your physician will view the inside of the rectum and lower part of the colon, either through the sigmoidoscope eyepiece or on a TV monitor. If your physician notes any polyps or abnormal tissue, a biopsy will be performed. This involves removing a sample of the tissue and sending it to a medical lab to determine whether cancer is present. If your physician identifies any polyps that need to be removed, he or she may recommend a second procedure - a colonoscopy - for this purpose. This is an invasive procedure and does carry some small risk such as infection, bleeding or perforation of the colon.