Diagnostic Tests

What Physicians Need to Know

CT Colonography for Colorectal Cancer Screening


Am Fam Physician. 2021 Jan 1;103(1):55-56.

Computed tomography (CT) colonography, or virtual colonoscopy, was developed in the mid-1990s and approved by the U.S. Food and Drug Administration for colorectal cancer screening in 2006.1 Patient preparation for the study typically includes using a bowel cathartic. Following ingestion of oral contrast, insufflation of gas via the rectum, and CT of the abdomen, specialized computer software reconstructs the images to create a two- or three-dimensional image of the colon.

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CT colonography

Screening for colorectal cancer

Adults 50 to 75 years of age


*—Information obtained at https://healthcarebluebook.com (accessed November 17, 2020; zip code: 66211).


CT colonography

Screening for colorectal cancer

Adults 50 to 75 years of age


*—Information obtained at https://healthcarebluebook.com (accessed November 17, 2020; zip code: 66211).


Studies of CT colonography have reported a wide range of sensitivities and specificities, possibly because of differences in study design, protocols for reading imaging or test results, radiologist experience, bowel preparation, or fecal tagging (ingestion of oral contrast).

In a meta-analysis including 11,151 patients, the sensitivity of CT colonography for the detection of colorectal cancer was 96.1% (95% CI, 93.8% to 97.7%), which is similar to optical colonoscopy.2 CT colonography is less accurate for detecting polyps. In a subsequent meta-analysis, the sensitivity of CT colonography for the detection of polyps 6 mm or larger was 73% to 98%; specificity ranged from 79.6% to 93.1%.3

Accuracy of CT colonography depends on the experience of the radiologist. To perform and interpret the test, radiologists must have specific initial training that includes at least 50 cases, as well as ongoing certification.1 Overall, improvements to CT colonography over the past two decades have yielded performance similar to optical colonoscopy.1

Reporting of CT colonography results has been standardized by use of the CT Colonography Reporting and Data System (C-RADS): C0 = technically inadequate, C1 = absence of polyps larger than 5 mm, C2 = one or two small polyps (6 mm to 9 mm), C3 = large polyps (10 mm or larger), and C4 = mass lesions (3 cm or larger).

A higher C-RADS category translates to higher risk of advanced neoplasia. Among patients with C2 findings, 5.8% had advanced neoplasia on optical colonoscopy, compared with 67.1% and 79.4% of patients with C3 or C4 findings, respectively.4


CT colonography offers important advantages over optical colonoscopy. As with stool testing, CT colonography has essentially no risk of bleeding or perforation, does not require sedation, and does not require interruption of therapeutic anticoagulation. CT colonography takes about 15 minutes to perform and offers more detailed findings (e.g., size, volume, location, and number of polyps) than

Address correspondence to Carl Bryce, MD, FAAFP, at carl.bryce@abrazohealth.com. Reprints are not available from the authors.

Author disclosure: No relevant financial affiliations.


show all references

1. Pickhardt PJ, Yee J, Johnson CD. CT colonography: over two decades from discovery to practice. Abdom Radiol (NY). 2018;43(3):517–522....

2. Pickhardt PJ, Hassan C, Halligan S, et al. Colorectal cancer: CT colonography and colonoscopy for detection—systematic review and meta-analysis. Radiology. 2011;259(2):393–405.

3. Lin JS, Piper MA, Perdue LA, et al. Screening for colorectal cancer: updated evidence report and systematic review for the US Preventive Services Task Force [published corrections appear in JAMA. 2016;316(5):545 and JAMA. 2016;316(13):1412]. JAMA. 2016;315(23):2576–2594.

4. Pickhardt PJ, Correale L, Hassan C. Positive predictive value for colorectal lesions at CT colonography: analysis of factors impacting results in a large screening cohort [published online April 11, 2019]. AJR Am J Roentgenol. Accessed November 20, 2020. https://www.ajronline.org/doi/10.2214/AJR.18.20686

5. Bibbins-Domingo K, Grossman DC, Curry SJ, et al. Screening for colorectal cancer: US Preventive Services Task Force recommendation statement [published corrections appear in JAMA. 2016;316(5):545 and JAMA. 2017;317(21):2239]. JAMA. 2016;315(23):2564–2575.

6. American Academy of Family Physicians. Colorectal cancer screening, adults. Clinical preventive service recommendation. Accessed October 1, 2020. https://www.aafp.org/family-physician/patient-care/clinical-recommendations/all-clinical-recommendations/colorectal-cancer-adults.html

7. Ebell MH, Thai TN, Royalty KJ. Cancer screening recommendations: an international comparison of high income countries. Public Health Rev. 2018;39:7.

8. Plumb AA, Boone D, Fitzke H, et al. Detection of extracolonic pathologic findings with CT colonography: a discrete choice experiment of perceived benefits versus harms. Radiology. 2014;273(1):144–152.

9. de González AB, Kim KP, Knudsen AB, et al. Radiation-related cancer risks from CT colonography screening: a risk-benefit analysis. AJR Am J Roentgenol. 2011;196(4):816–823.

10. Healthcare Bluebook. Accessed November 17, 2020. https://www.healthcarebluebook.com. (zip code: 66211)

11. Centers for Medicare and Medicaid Services. 20CL ABQ2. Accessed November 19, 2020. https://www.cms.gov/medicaremedicare-fee-service-paymentclinicallabfeeschedclinical-laboratory-fee-schedule-files/20clabq2

This series is coordinated by Kenny Lin, MD, MPH, deputy editor.

A collection of Diagnostic Tests published in AFP is available at https://www.aafp.org/afp/diagnostic.



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