Last reviewed: June 21, 2026 · Clinical reviewer: Diagnostic Orders Direct provider team
What Is CT Colonography?
CT colonography — also called virtual colonoscopy — is a CT-based imaging study that examines the colon and rectum for polyps and colorectal cancer. It uses low-dose CT imaging to create detailed pictures of the inside of the colon. The procedure typically takes 10–15 minutes and does not require sedation.
CT colonography involves bowel preparation, gas or air insufflation to expand the colon, and sometimes oral contrast tagging agents. It is listed by the USPSTF as one recommended colorectal cancer screening strategy for eligible average-risk adults, typically every 5 years.
What Is Conventional Colonoscopy?
Conventional colonoscopy is a procedure in which a gastroenterologist inserts a flexible tube with a camera (colonoscope) through the rectum to examine the entire colon. It typically requires sedation and takes 30–60 minutes. Unlike CT colonography, conventional colonoscopy can both detect and removepolyps and take biopsies during the same procedure.
Conventional colonoscopy is generally recommended every 10 years for average-risk adults, or more frequently for patients with risk factors, prior polyps, or family history.
Key Differences at a Glance
| Feature | CT Colonography | Conventional Colonoscopy |
|---|---|---|
| Sedation | No sedation required | Typically requires sedation |
| Duration | 10–15 minutes | 30–60 minutes |
| Polyp removal | Cannot remove polyps | Can remove polyps during procedure |
| Biopsy | Cannot take biopsies | Can take biopsies during procedure |
| Follow-up needed | Abnormal findings may require colonoscopy | Polyps removed during procedure |
| Screening interval | Typically every 5 years | Typically every 10 years |
| Bowel prep | Required (often less extensive) | Required |
| Radiation | Low-dose CT radiation | No radiation |
Advantages of CT Colonography
No sedation — you can drive yourself home and resume normal activities immediately
Shorter procedure time (10–15 minutes)
May be an option for patients who are not candidates for conventional colonoscopy
Can detect polyps and masses in the colon
Less invasive than conventional colonoscopy
Limitations of CT Colonography
Cannot remove polyps — if polyps are found, you may need a conventional colonoscopy
Cannot take biopsies — tissue sampling requires conventional colonoscopy
Involves low-dose radiation (conventional colonoscopy does not)
May detect incidental findings outside the colon that require follow-up
May be less sensitive for very small polyps compared to conventional colonoscopy
Why Abnormal CT Colonography May Require Colonoscopy
If CT colonography detects a polyp or suspicious finding, the next step is typically a conventional colonoscopy to remove the polyp or take a biopsy. This means some patients who choose CT colonography may end up needing both procedures. This is not a failure of CT colonography — it is how the screening pathway works.
The CDC notes that abnormal results on some screening tests, including CT colonography, may require colonoscopy to complete the screening process. This is an important consideration when choosing a screening method.
Neutral note: Both CT colonography and conventional colonoscopy are accepted colorectal cancer screening options. Neither is universally "better" — the right choice depends on your individual risk profile, preferences, medical history, and what your provider recommends. DOD does not recommend one over the other. Always discuss screening options with your treating providers.
Red-Flag Symptoms — Do Not Use This Routine Screening Workflow
If you have any of the following, seek appropriate primary care, gastroenterology, urgent care, or emergency evaluation rather than using a routine preventive screening order workflow:
- •Rectal bleeding or black/tarry stool
- •Unexplained weight loss
- •Iron-deficiency anemia or abnormal blood counts needing workup
- •Severe or worsening abdominal pain
- •Bowel obstruction symptoms, persistent vomiting, or inability to pass stool/gas
- •New major bowel habit change with systemic symptoms
- •Known inflammatory bowel disease flare or complex GI history
- •Prior colorectal cancer or high-risk hereditary cancer syndrome concern
- •Pregnancy or possible pregnancy (must be reviewed before CT imaging)
Patients with concerning symptoms should seek appropriate medical evaluation, not a routine preventive screening order. Call 911 for emergencies.