Atrium Health Navicent Gastroenterology & Hepatology

Flex Sig

Doctor close up with patients in the background

A flexible sigmoidoscopy, or flex sig, is a procedure a health care provider uses to look inside the final third of the colon, known as the sigmoid colon. Using a narrow, flexible tube with a light and tiny camera on one end, called a scope, the health care provider looks for such conditions as cancer and pieces of tissue growing on the inner lining of the colon, known as polyps. The flexible sigmoidoscope has largely replaced the rigid sigmoidoscope, which cannot reach so far into the colon as the flexible scope can.

A health care provider will perform a flexible sigmoidoscopy if a patient displays such symptoms as abdominal pain, weight loss, colitis, and diarrhea, changes in bowel habits or rectal bleeding. A health care provider will sometimes perform a flex sig as a screening for colon cancer in order to detect early stages of the disease.

Flex Sig Prep

From one to three days prior to a flex sig procedure, the patient must follow a clear liquid diet. He can only consume such liquids as water, prepared gelatin, apple or white grape juice, clear broth, plain tea or coffee and sports drinks that contain vital electrolytes. He needs to avoid red gelatin and red or purple drinks, which can appear as blood within the colon. The patient will usually also need to mix a powder laxative in liquid to expedite emptying the colon.


The health care provider will usually perform a flex sig at a hospital outpatient center. The patient will not need general anesthesia but will often be under light sedation. As the patient lies on his left side on a table, the health care provider advances the scope into the rectum and carefully guides it into the lower colon. The scope inflates the intestine and the attached camera sends an image of the intestinal lining to a computer monitor. Viewing the monitor, the health care provider examines the tissue for abnormalities. He may at times need to move the patient to adjust the scope in order to see a clearer picture. When the scope reaches the transverse colon, the health care provider slowly withdraws it and further examines the lining of the sigmoid colon. Normally, the procedure takes no more than 20 minutes.

If the health care provider finds any growths, polyps or other abnormalities, he may remove them or other small pieces of tissue and send them to a lab for further testing. If bleeding occurs during this procedure, the health care provider can stop the bleeding either with medication passed through the scope or with an electrical probe.

Following a flex sig, the patient can expect to experience abdominal bloating or cramps for an hour or two due to the air the health care provider inserted into the colon. This feeling should gradually leave as the patient passes gas. The health care provider will discuss the immediate results of the test with the patient. If tissue was sent to a lab, the patient can expect those results at a later time.

Risks of a Flexible Sigmoidoscopy

The most common complications of a flex sig are bleeding or perforation of the lining of the colon. Other rare, yet more serious, complications include severe abdominal pain; diverticulitis, or irritation, swelling or infection of pouches in the wall of the colon; and such cardiovascular conditions as low blood pressure or heart attack. If the patient experiences any of these conditions, fever, bloody stool, weakness, or dizziness, he should immediately seek care.

Flexible Sigmoidoscopy vs. Colonoscopy

Because a colonoscopy allows the health care provider to view the entire colon, many prefer it as a screening method to the flex sig. However, the flex sig is less invasive, takes less time, and is less costly.

Various health care providers, such as general or family practitioners, internal medicine physicians, nurse practitioners and physician's assistants, may perform flex sigs. Gastroenterologists or surgeons usually perform colonoscopies.

Medical experts differ as to the preferred method of screening. Because a flex sig only examines the left side of the colon, this procedure is unable to reveal problems in the remaining portions of the colon. A colonoscopy is able to detect problems within the entire colon. Provided they do not have blood in the stool, patients who are concerned about issues peculiar to a colonoscopy, such as cost, harsh prep, danger of severe perforation or potential side effects of anesthesia, may opt to go for a flex sig.

A responsible healthcare provider will explain in depth the pros and cons of both procedures to their patient but will ultimately let the patient make the decision which procedure they choose to undergo.