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Am Fam Physician. 2020;102(4):250-252

Author disclosure: No relevant financial affiliations.

Key Points for Practice

• Screening reduces CRC mortality in patients 50 to 75 years of age, with greatest benefit in patients older than 60 years.

• The ACP recommends screening average-risk patients with one of the following: colonoscopy every 10 years, flexible sigmoidoscopy every 10 years with biennial FIT, biennial guaiac FOBT, or biennial FIT.

• Because of limited evidence of benefit and increased harms, neither FIT with stool DNA testing nor CT colonography is a recommended screening method.

From the AFP Editors

Colorectal cancer (CRC) is the second leading cause of cancer death in the United States. Up to 80% of CRC develops from colonic adenomas over five to 20 years, illustrating the potential benefit of early detection. Only 10% of adenomas progress to CRC over 10 years; the rest stabilize or regress. The American College of Physicians (ACP) developed a consensus statement for CRC screening of average-risk adults based on their review of six independent guidelines and supporting evidence. People at elevated risk are subject to other screening recommendations and are not addressed here.

Overall Recommendations

The ACP recommends routine screening of average-risk adults between 50 and 75 years of age to reduce CRC mortality. Screening is not recommended after 75 years of age or when life expectancy is less than 10 years. Several screening methods are recommended (Table 1), with decisions based on patient preferences.

Screening methodRecommended screening intervalNumber needed to screen to prevent one death from colorectal cancerPatient benefitsImportant harms
ColonoscopyEvery 10 yearsUnknownDefinitive studyRequires colon preparation and anesthesia
Risk of colon perforation (NNH = 384 to 2,500)
Risk of major bleeding (NNH = 294 to 1,250)
Flexible sigmoidoscopy and FITFlexible sigmoidoscopy every 10 years and FIT every two years850 over 11 years (flexible sigmoidoscopy alone); 2,000 for < 60 years; 345 for ≥ 60 yearsProven mortality benefitRequires colon preparation
Often requires anesthesia
Risk of major bleeding (NNH = 5,000)
Will miss proximal disease; recommended with biennial FIT
FITEvery two yearsUnknownNo colon preparation
Single stool sample
No dietary restrictions
False-negative test results are less than one in 1,000
One false positive in every 11 tests requires unnecessary colonoscopy
Guaiac fecal occult blood testingEvery two years377 over 18 yearsProven mortality benefit
No colon preparation
Dietary restrictions
Multiple stool samples
One in 182 tests will be a false negative, missing cancer
One in 82 tests will be a false positive that requires unnecessary colonoscopy
Not recommended
FIT with stool DNAEvery three yearsUnknownNo colon preparation
Single stool sample
No dietary restrictions
Predicts fewer false-negative test results than FIT
Specificity lower than FIT, increasing false positives that require unnecessary colonoscopy
Positive stool DNA result may lead to overly aggressive testing
Computed tomography colonographyEvery five yearsUnknownAccuracy similar to colonoscopyRequires colon preparation
Radiation exposure
Positive test results require colonoscopy
Incidental extracolonic findings in up to 69% of tests

Recommended Screening Tests with Strong Evidence


Colonoscopy is accurate in detecting adenomas but has no evidence of decreasing CRC-related mortality. Colonoscopy detects adenomas measuring 10 mm or larger with 89% to 98% sensitivity and 75% to 93% sensitivity for adenomas measuring at least 6 mm. Mortality benefit from colonoscopy is suggested by modeling studies and the proven benefit of flexible sigmoidoscopy.

Harms of colonoscopy include perforation and major bleeding. Perforation occurs in four to 14 per 10,000 procedures, and major bleeding occurs in eight to 34 per 10,000 procedures. Because other screening methods lead to colonoscopy when test results are positive, harms of all testing include those of colonoscopy.


Flexible sigmoidoscopy is one of few screening methods proven to reduce CRC mortality, with a number needed to screen of 850 to prevent one CRC death over 11 years. Benefits of flexible sigmoidoscopy increase with advanced age; the number needed to screen is 344 for people 60 years and older but is 2,000 for people younger than 60. Because flexible sigmoidoscopy reduces CRC mortality only in the distal colon, concurrent use of biennial fecal immunochemical testing (FIT) is recommended to increase identification of pathology outside the distal colon.

The advantage of flexible sigmoidoscopy over colonoscopy is a lower likelihood of harm. Colon perforation has not been reported in studies. Bleeding risk is one-fourth of the risk from colonoscopy, with two major bleeds for every 10,000 flexible sigmoidoscopies.


A simple, noninvasive screening method, guaiac fecal occult blood testing (FOBT) is also proven to reduce CRC mortality. Although the number needed to screen for guaiac FOBT is 377 over 18 years for patients 45 to 80 years of age, the primary benefit occurs in patients 60 years and older. Biennial guaiac FOBT is recommended over annual screening because of similar CRC mortality. For every 1,000 tests, 12 results will be false positives and six will be false negatives.


Another stool-based test, FIT eliminates dietary restrictions and multiple samples required for guaiac FOBT. FIT is more accurate than guaiac FOBT, resulting in fewer missed cancers but causes many more false-positive results. For every 1,000 patients who receive FIT, less than one will have a false-negative result, but 88 will have false-positive results, leading to more unnecessary colonoscopies.

Screening Tests Not Recommended Because of Limited Evidence


Based on a single study, combining stool DNA and FIT moderately increases sensitivity with the cost of reduced specificity. Although evidence is lacking, the reduced specificity should exacerbate the high false-positive FIT rate. Positive stool DNA results may lead to more aggressive surveillance without proven benefit.


Computed tomography (CT) colonography appears to have similar accuracy to colonoscopy, with 67% to 94% sensitivity and 86% to 98% specificity for adenomas measuring 10 mm and larger. Clinical benefits of CT colonography have not been studied. Patients require bowel preparation again for follow-up colonoscopy if results are positive. In addition to radiation exposure risks, harms of CT colonography include extracolonic findings in up to 69% of patients, which commonly require further diagnostic workup.

Editor's Notes: The numbers needed to screen and numbers needed to harm were calculated by the author based on data provided in the original ACP guideline.

CRC screening guidelines vary because of organization priorities and evidence limitations. To create these recommendations, the ACP reviewed cited evidence from the American College of Radiology, the Canadian Task Force on Preventive Health Care, the U.S. Preventive Services Task Force (USPSTF), the American Cancer Society, the Scottish Intercollegiate Guidelines Network, and the U.S. Multi-Society Task Force on Colorectal Cancer. The ACP was not able to perform a meta-analysis but cited the best evidence found. The AAFP endorses the 2016 USPSTF recommendations to screen patients between 50 and 75 years of age with FIT, flexible sigmoidoscopy, or colonoscopy and to consider screening patients between 76 and 85 years of age.—Michael J. Arnold, MD, contributing editor

Guideline source: American College of Physicians

Evidence rating system used? Yes

Systematic literature search described? No

Guideline developed by participants without relevant financial ties to industry? Yes

Recommendations based on patient-oriented outcomes? Yes

Published source: Ann Intern Med. November 5, 2019;171(9):643–654

Coverage of guidelines from other organizations does not imply endorsement by AFP or the AAFP.

This series is coordinated by Michael J. Arnold, MD, associate medical editor.

A collection of Practice Guidelines published in AFP is available at

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