Flexible Sigmoidoscopy in Dallas & Sachse, TX

Medically reviewed by Jaison John, MD — Board-Certified Gastroenterologist
Last updated: March 2026

What Is a Flexible Sigmoidoscopy?

A flexible sigmoidoscopy is a diagnostic procedure that allows a gastroenterologist to examine the lining of the rectum, sigmoid colon, and descending colon — the lower third of the large intestine — using a thin, flexible, lighted instrument called a sigmoidoscope. The sigmoidoscope is a shorter version of the colonoscope, typically measuring about 60 centimeters (approximately 2 feet) in length, equipped with a camera and light at its tip that transmits real-time video to a monitor.

Unlike a colonoscopy, which examines the entire colon from the rectum to the cecum (approximately 5 to 6 feet), a sigmoidoscopy focuses on the distal (lower) colon, where a significant proportion of colorectal pathology — including polyps, cancers, and inflammatory changes — tends to occur. Studies have shown that approximately 60% to 70% of colorectal polyps and cancers are located within the reach of a sigmoidoscope.

Flexible sigmoidoscopy has been used for decades as both a diagnostic and screening tool. The American Cancer Society (ACS) and the U.S. Preventive Services Task Force (USPSTF) recognize flexible sigmoidoscopy (performed every 5 years, or every 10 years when combined with annual FIT testing) as an acceptable colorectal cancer screening option, although colonoscopy remains the preferred and most comprehensive screening method as endorsed by the American College of Gastroenterology (ACG).

At Texas Gut Health in Sachse, TX, Dr. Jaison John performs flexible sigmoidoscopy for patients who require targeted evaluation of the lower colon. Dr. John completed his gastroenterology fellowship at UT Medical Branch, where he served as Chief Fellow, and his internal medicine residency at UT Austin Dell Medical School, where he served as Chief Resident. He holds dual board certifications from the American Board of Internal Medicine in both internal medicine and gastroenterology.

Sigmoidoscopy vs. Colonoscopy

Understanding the differences between a sigmoidoscopy and a colonoscopy can help you and your physician determine which procedure is most appropriate for your situation.

• Scope of examination: A colonoscopy examines the entire colon and rectum (approximately 150 cm). A sigmoidoscopy examines only the rectum, sigmoid colon, and descending colon (approximately 60 cm) — the lower third of the large intestine.
• Bowel preparation: Colonoscopy requires a full bowel preparation, including a clear liquid diet and a laxative solution the day before the procedure. Sigmoidoscopy typically requires only one or two enemas administered 1 to 2 hours before the procedure, making preparation significantly easier.
• Sedation: Colonoscopy is performed with intravenous sedation. Sigmoidoscopy can often be performed without sedation, though sedation is available for patients who prefer it.
• Procedure time: Colonoscopy typically takes 30 to 60 minutes. Sigmoidoscopy takes approximately 10 to 20 minutes.
• Recovery: After a colonoscopy, patients need 30 to 60 minutes of monitored recovery time due to sedation and cannot drive for the remainder of the day. After a sigmoidoscopy without sedation, patients can typically resume all normal activities immediately, including driving.
• Diagnostic completeness: Colonoscopy provides a complete evaluation of the entire colon. Sigmoidoscopy evaluates only the lower third, meaning pathology in the transverse colon, ascending colon, or cecum will not be detected.
• Cancer screening effectiveness: Randomized controlled trials published in the New England Journal of Medicine and The Lancet have shown that sigmoidoscopy screening reduces colorectal cancer incidence by 18% to 23% and mortality by 26% to 31%. Colonoscopy, while not yet supported by completed randomized trials of comparable size, is estimated to reduce colorectal cancer incidence by 40% to 90% because it examines the entire colon.

While colonoscopy is the more comprehensive procedure, sigmoidoscopy remains a valuable tool for specific clinical situations and for patients who may benefit from a less invasive evaluation of the lower colon.

Why Sigmoidoscopy Is Performed

Dr. John may recommend a flexible sigmoidoscopy for several reasons:

• Evaluation of lower GI symptoms: Symptoms such as rectal bleeding, left-sided abdominal pain, changes in bowel habits, or mucous discharge may originate in the lower colon or rectum. A sigmoidoscopy can quickly identify the cause without requiring full bowel preparation or sedation.
• Surveillance for ulcerative colitis — Patients with left-sided or distal ulcerative colitis (disease confined to the rectum and sigmoid colon) may undergo periodic sigmoidoscopy to assess disease activity, mucosal healing, and response to treatment.
• Follow-up after radiation therapy: Patients who have received pelvic radiation (for prostate, cervical, or rectal cancer) may develop radiation proctitis or proctosigmoiditis, which can be evaluated and sometimes treated during a sigmoidoscopy.
• Evaluation of rectal bleeding in younger patients: In younger adults with bright red rectal bleeding and a low pretest probability for proximal colon pathology, a sigmoidoscopy may be appropriate as a first-line evaluation to rule out conditions such as proctitis, internal hemorrhoids, or rectal ulcers.
• Colorectal cancer screening (alternative method): The USPSTF recognizes sigmoidoscopy every 5 years (or every 10 years combined with annual FIT) as an acceptable screening option for average-risk adults. While colonoscopy is preferred by the ACG, sigmoidoscopy offers a less invasive option for patients who decline or cannot undergo colonoscopy.
• Confirmation of findings from imaging or stool tests: Abnormalities detected on imaging studies or positive stool-based screening tests affecting the distal colon may be further evaluated with a sigmoidoscopy, though a full colonoscopy is generally preferred for complete evaluation.

What to Expect

Flexible sigmoidoscopy is a quick, straightforward procedure with minimal preparation. Here is what the experience looks like at Texas Gut Health.

Before Your Sigmoidoscopy

One of the major advantages of sigmoidoscopy over colonoscopy is the simplified preparation:

• Enema preparation: In most cases, you will administer one or two Fleet (sodium phosphate) enemas at home approximately 1 to 2 hours before your appointment. These enemas clear the lower colon so the physician can see the lining clearly. Detailed instructions will be provided by our office.
• No full bowel prep required: Unlike a colonoscopy, sigmoidoscopy does not require a clear liquid diet, a large-volume laxative solution, or overnight fasting (in most cases).
• Medication review: Inform Dr. John about all medications you take, especially blood thinners, as they may need to be adjusted if biopsies or polyp removal are anticipated.
• Transportation: If the procedure is performed without sedation, you can drive yourself to and from the appointment. If you prefer sedation, you will need a responsible adult to drive you home.

During the Procedure

A flexible sigmoidoscopy typically takes 10 to 20 minutes:

• Positioning: You will be positioned comfortably on your left side on an examination table with your knees drawn toward your chest.
• Scope insertion: Dr. John will gently insert the lubricated sigmoidoscope through the rectum and advance it through the sigmoid colon and, if indicated, into the descending colon. A small amount of air may be introduced to expand the colon for better visualization.
• Examination: The camera at the tip of the scope transmits high-definition images to a monitor, allowing Dr. John to inspect the colon lining in real time. He will look for polyps, areas of inflammation, ulcers, bleeding sources, and other abnormalities.
• Biopsies and polyp removal: If polyps or suspicious tissue are found, Dr. John may take biopsies or remove small polyps using instruments passed through the scope. The tissue is sent to a pathology lab for analysis.
• What you may feel: You may experience mild cramping, pressure, or a sensation of needing to have a bowel movement as the scope is inserted and air is introduced. These sensations are brief and typically resolve as soon as the scope is removed. Taking slow, deep breaths can help minimize discomfort.

After Your Sigmoidoscopy

Recovery from a sigmoidoscopy is rapid:

• Without sedation: You can get dressed and leave the office within minutes of the procedure. There are no activity restrictions, and you can eat, drink, and drive normally.
• With sedation: If sedation was used, you will be monitored in a recovery area for 30 to 60 minutes and will need a driver to take you home.
• Mild symptoms: You may experience mild bloating, gas, or cramping for a few hours after the procedure as the air introduced during the exam is expelled. This is normal and resolves quickly.
• Results: Dr. John will share preliminary findings with you immediately after the procedure. If biopsies were taken, pathology results are typically available within 1 to 2 weeks.
• Follow-up colonoscopy: If polyps, significant inflammation, or other abnormalities are found during the sigmoidoscopy, Dr. John may recommend a full colonoscopy to examine the remainder of the colon.

Conditions Diagnosed or Evaluated

Flexible sigmoidoscopy can help diagnose, evaluate, or monitor a range of conditions affecting the lower colon and rectum:

• Colorectal cancer and polyps — Sigmoidoscopy can detect cancers and precancerous polyps in the rectum, sigmoid colon, and descending colon. Finding polyps in the distal colon often prompts a full colonoscopy to check the rest of the colon.
• Ulcerative colitis — Sigmoidoscopy is commonly used to evaluate and monitor disease activity in patients with left-sided or distal ulcerative colitis. It allows the physician to assess mucosal inflammation, take biopsies, and evaluate response to treatment without requiring full bowel preparation.
• Proctitis — Inflammation of the rectal lining can result from infection, radiation therapy, inflammatory bowel disease, or other causes. Sigmoidoscopy provides direct visualization and biopsy capability for accurate diagnosis.
• Radiation proctitis — Patients who have received pelvic radiation may develop chronic inflammation, bleeding, and telangiectasias (abnormal blood vessels) in the rectum. Sigmoidoscopy can diagnose and, in some cases, treat these changes using argon plasma coagulation or other endoscopic techniques.
• Rectal bleeding evaluation — Sigmoidoscopy can identify the source of bright red rectal bleeding, including hemorrhoids, rectal ulcers, polyps, proctitis, or colitis in the distal colon.
• Diverticular disease — The sigmoid colon is the most common location for diverticulosis (small pouches in the colon wall). Sigmoidoscopy can evaluate patients with left-sided symptoms or a history of diverticulitis.
• Solitary rectal ulcer syndrome — This condition, often associated with chronic straining, involves an ulcer on the rectal wall that can cause bleeding and mucous discharge. Sigmoidoscopy with biopsy is used for diagnosis.

Risks and Benefits

Flexible sigmoidoscopy is a well-established, safe procedure. Understanding the benefits and potential risks helps patients make informed decisions.

Benefits

• Minimal preparation: Only an enema is required in most cases — no full bowel prep, no clear liquid diet, and no overnight fasting.
• Quick procedure: The exam takes only 10 to 20 minutes, significantly shorter than a colonoscopy.
• Sedation often not needed: Most patients tolerate the procedure well without sedation, eliminating the need for a driver, IV placement, and post-sedation recovery time.
• Immediate return to activities: Without sedation, patients can drive, eat, and resume all activities immediately after the procedure.
• Proven cancer screening tool: Randomized trials have demonstrated that sigmoidoscopy screening reduces colorectal cancer incidence and mortality.
• Diagnostic and therapeutic: Biopsies and small polyp removal can be performed during the same procedure.

Risks

Serious complications from flexible sigmoidoscopy are uncommon. The overall complication rate is lower than that of colonoscopy due to the shorter extent of the examination. Potential risks include:

• Discomfort and cramping: Mild cramping during and briefly after the procedure is common and expected. It is not a complication but a normal response to the scope and air insufflation.
• Bleeding: Minor bleeding may occur if biopsies are taken or polyps are removed. Significant bleeding is rare, occurring in less than 1 in 1,000 procedures.
• Perforation: A tear in the colon wall is the most serious potential complication but is extremely rare during sigmoidoscopy, occurring in approximately 1 in 10,000 to 1 in 25,000 procedures. If a perforation occurs, it may require hospitalization or surgical repair.
• Incomplete evaluation: Sigmoidoscopy examines only the lower third of the colon. Pathology in the upper portions of the colon will not be detected. If findings warrant, a full colonoscopy will be recommended.

Dr. John discusses all risks and benefits with each patient before the procedure. The ACG, ACS, and USPSTF affirm that flexible sigmoidoscopy is a safe procedure when performed by a trained gastroenterologist.

Frequently Asked Questions