Endoscopy 101 (Colonoscopy, Flex Sig)

Endoscopy lets clinicians see the inside lining of the bowel to diagnose inflammatory bowel disease and to track healing over time. Colonoscopy views the entire colon and often the last part of the small bowel. Flexible sigmoidoscopy views the rectum and left side only. What is seen on these scopes, and what biopsies show, guides treatment choices and treat‑to‑target plans. (journals.lww.com)

Key takeaways

• Colonoscopy examines the whole colon, flexible sigmoidoscopy looks at the left side only. Both can take biopsies. (journals.lww.com)

• Split‑dose bowel prep, part the evening before and part 4–6 hours before, improves exam quality. (gastro.org)

• In severe hospitalized ulcerative colitis, early flexible sigmoidoscopy with biopsies is preferred. (journals.lww.com)

• Endoscopic scores, like Mayo (UC) and SES‑CD (Crohn’s), help gauge severity and adjust therapy. (academic.oup.com)

• Scopes are safe. Serious complications like perforation are rare. Know after‑procedure red flags. (journals.lww.com)

What these tests are

• Colonoscopy uses a thin, flexible camera to inspect the rectum and entire colon, and often the terminal ileum. Tools through the scope allow biopsies and treatment if needed. Most people receive sedation, the test usually takes 30 to 45 minutes, and someone must drive them home. (asge.org)

• Flexible sigmoidoscopy uses a shorter scope to view the rectum and left colon. It is often done with little or no sedation and minimal or no bowel prep, especially in severe colitis. (journals.lww.com)

Before the scope: prep and medications

• Quality prep matters. The U.S. Multi‑Society Task Force now recommends split‑dose regimens for most people. Take the second dose 4 to 6 hours before start time and finish at least 2 hours before the procedure. Same‑day regimens are reasonable for afternoon appointments. Centers increasingly allow a limited low‑residue diet the day before. Follow local instructions. (gastro.org)

• Medication plans are individualized. Endoscopy teams will review blood thinners, diabetes drugs, and drugs like GLP‑1 receptor agonists. Ensure written instructions are provided and an escort is arranged. (journals.lww.com)

During the scope: what happens

• Vital signs are monitored. Sedation is given for comfort. Many units use carbon dioxide instead of air to inflate the bowel, which reduces post‑procedure bloating and pain without affecting exam quality. Biopsies are taken with small forceps and usually are not felt. (pubmed.ncbi.nlm.nih.gov)

• In severe hospitalized ulcerative colitis, a flexible sigmoidoscopy is done early, with minimal air and without full prep, to reduce risk. Biopsies check for cytomegalovirus if suspected. (journals.lww.com)

What clinicians look for

• Distribution and appearance help distinguish conditions. Ulcerative colitis usually looks continuous from the rectum. Crohn’s can have patchy “skip” areas, deeper ulcers, and strictures. Multiple biopsies are taken across the colon and terminal ileum when feasible to confirm diagnosis and map extent. (academic.oup.com)

• Severity is often summarized with endoscopic scores:

• Mayo endoscopic subscore (UC) ranges 0 to 3. Lower is better.

• UCEIS (UC) also grades severity and can predict outcomes in severe colitis.

• SES‑CD (Crohn’s) adds up ulcer size, ulcerated area, affected area, and narrowing across segments. Lower scores mean milder disease. (academic.oup.com)

How findings guide treatment

• IBD care follows treat‑to‑target. Long‑term goals include clinical remission and endoscopic healing. In practice, teams aim for Mayo 0–1 in UC and very low SES‑CD in Crohn’s, along with normal blood and stool markers. If healing is not reached, therapy is adjusted. (pubmed.ncbi.nlm.nih.gov)

• Examples:

• Mild proctitis may respond to rectal therapies.

• Moderate to severe ulcers or deep lesions often prompt escalation to advanced therapies.

• Post‑treatment scopes confirm healing or trigger changes. Shorter intervals between scopes and acting on results increase the chance of mucosal healing. (pubmed.ncbi.nlm.nih.gov)

Risks and safety

• Colonoscopy is very safe. Perforation during screening colonoscopy is generally under 0.1%, and bleeding is under 1% for diagnostic exams. Risk is higher when removing large polyps or in frail adults. Flexible sigmoidoscopy has even lower risks; perforation is rare. (journals.lww.com)

• After any sedated exam, do not drive, operate machinery, or make legal decisions that day. Call the care team or seek urgent care for severe belly pain, fever, persistent vomiting, heavy bleeding, or fainting. (asge.org)

After the scope: recovery and results

• Bloating and gas are common and usually fade within a day. Most people resume a normal diet after leaving the unit unless told otherwise. The doctor often shares a visual summary the same day. Biopsy results take a few days, then the team updates the treatment plan. (asge.org)

Colonoscopy vs flexible sigmoidoscopy

FAQs

Will everyone with IBD need colonoscopy rather than flex sig

At diagnosis, full colonoscopy with ileum biopsies is preferred when safe. In severe colitis, a limited sigmoidoscopy is safer at first. (journals.lww.com)

What if the prep is not adequate

Poor prep can hide inflammation. If cleansing is inadequate, the exam may be repeated, often with a modified split‑dose plan. (gastro.org)

Does the type of gas used matter

Yes. Using carbon dioxide instead of air reduces post‑procedure pain and bloating without changing detection rates. Many centers use it routinely. (pubmed.ncbi.nlm.nih.gov)