Putting Prevention into Practice

Screening for Colorectal Cancer


Am Fam Physician. 2000 Jun 1;61(11):3477-3480.

Case Study 1

SE is a 69-year-old man who has never been screened for colorectal cancer. After conducting a history and physical examination, it appears that he is not at high risk for colorectal cancer.

Case Study 2

SD is a 53-year-old woman who has been followed in your office since presenting with perimenopausal symptoms for about two years. She has a history of ulcerative colitis. Aside from being severely overweight, she has no active medical problems. During her visit today, she notes that a 48-year-old sibling recently underwent surgical treatment for colon cancer. A review of the chart reveals that an older sister is being treated for hypertension, and her parents are both deceased because of cardiac events in their 70s. She inquires about the likelihood of developing colon cancer herself. Her physical examination is unremarkable.

Case Study 1 Questions

  1. An average-risk person should begin screening for colorectal cancer at which one of the following ages?

    • A. 40 years.

    • B. 45 years.

    • C. 50 years.

    • D. 55 years.

    • E. 65 years.

  2. For SE, which one of the following statements is incorrect?

    • A. A digital rectal examination should be among the first tests performed.

    • B. A fecal occult blood test should be among the first tests performed.

    • C. A sigmoidoscopy should be among the first tests performed.

    • D. Dietary iron does not cause false-positive results on fecal occult blood tests.

    • E. A positive result on even one sample qualifies the entire test as positive.

Case Study 2 Questions

  1. Which of the following factors indicate a need for screening?

    • A. More than 50 years of age.

    • B. Severely overweight.

    • C. First-degree relative with colorectal cancer.

    • D. History of ulcerative colitis.

  2. Which of the following steps should be considered next?

    • A. Barium enema.

    • B. Endoscopic examination.

    • C. Digital rectal examination.

    • D. Referral to a subspecialist.


1. The answer is C: colorectal cancer screening is recommended for all persons 50 years and older. Before testing, patients should understand the purpose of various screening tests for colorectal cancer. They should also be told what to expect during these tests and about any possible complications relating to the tests. Physicians should highlight the possibility of a positive result (as a true-positive or a false-positive), along with additional testing that might be indicated. For example, fecal occult blood testing (FOBT) has a reported sensitivity ranging from 26 to 92 percent.16 Because the vast majority of positive FOBT results are false-positives, the likelihood that a positive test indicates cancer is relatively low.14

Patients at increased risk of colorectal cancer, because of having a first-degree relative with colorectal cancer, hereditary syndromes, ulcerative colitis or other conditions, may warrant referral to subspecialists for earlier and more aggressive surveillance.

2. The answer is A: digital rectal examination (DRE) can assess only the most terminal aspect of the rectum; thus, this screening technique is believed to be of limited value. Over the past several years, there has been a shift of tumors from the rectum and descending colon toward more proximal lesions in the ascending colon. It is estimated that fewer than 10 percent of colorectal cancers could be palpated using DRE.5

Screening for colorectal cancer is recommended for all persons 50 years and older with annual FOBT or sigmoidoscopy, or both. There is insufficient evidence to determine which of these screening methods is preferable or whether the combination of FOBT and sigmoidoscopy produces greater benefits than either test alone. Although there is good evidence to support use of FOBT on an annual basis, there is insufficient evidence to recommend a periodicity for sigmoidoscopy screening. Scientific evidence supporting barium enema or colonoscopy as routine screening is more limited.

If a single test panel for a FOBT is positive, follow-up requires diagnostic procedures such as sigmoidoscopy, colonoscopy or barium enema. Likewise, positive results from flexible sigmoidoscopy also require colonoscopy.

False-positive results on guaiac card testing can result from ingestion of peroxidase-containing foods, gastric irritation from ingestion of salicylates, and nonsteroidal anti-inflammatory agents.1 Despite previous reports, dietary iron does not cause false-positive test results.

3. The answers are A, C and D: each of the answers represents established risk factors for colon cancer. Screening for colorectal cancer is recommended for all persons 50 years and older. In terms of quantifying risk, it is highest among persons with genetic syndromes such as hereditary polyposis and hereditary non-polyposis colorectal cancers, as well as among persons who have had longstanding ulcerative colitis.5,6 Additional risk factors include a first-degree relative (i.e., parent, sibling or child) with colorectal cancer and a past history of breast, ovarian or endometrial cancer. Other potential risk factors are less well established. Patients with an increased risk of developing colorectal cancer may warrant referral to a subspecialist for assessment and identification of a modified surveillance schedule. Patients found to have cancers of the colon and rectum demonstrate enhanced survival when disease is detected at earlier stages.

4. The answers are B and D: for persons at very high risk of colon cancer (e.g., ulcerative colitis or history consistent with familial syndromes such as familial polyposis or hereditary nonpolyposis colorectal cancer), regular endoscopic screening is part of the routine diagnosis and management. Referral to sub-specialists is appropriate for these high-risk patients. Referral is not necessarily indicated for patients whose only risk is a single affected family member, but it may be appropriate to begin screening earlier if a relative developed cancer at a younger age.


show all references

1. Winawer SJ, Fletcher RH, Miller L, Godlee F, Stolar MH, Mulrow CD, et al. Colorectal cancer screening: clinical guidelines and rationale. Gastroenterology. 1997;112:594–642....

2. Colorectal Cancer Screening, Technical Review 1. U.S. Department of Health and Human Services. Agency for Health Care Policy and Research, Rockville, Maryland. AHCPR Publication No. 98-0033, May 1998.

3. Ahlquist DA, Wieland HS, Moertel CG, McGill DB, Loprinzi CL, O'Connell MJ, et al. Accuracy of fecal occult blood screening for colorectal neoplasia: a prospective study using Hemoccult and HemoQuant tests. JAMA. 1993;269:1262–7.

4. St John DJB, Young GP, McHutchison JG, Deacon MC, Alexeyeff MA. Comparison of the specificity and sensitivity of Hemoccult and HemoQuant in screening for colorectal neoplasia. Ann Intern Med. 1992;117:376–82.

5. Selby JV, Friedman GD, Quesenberry CP, Weiss NS. Effect of fecal occult blood testing on mortality from colorectal cancer: a case-control study. Ann Intern Med. 1993;118:1–6.

6. Wahrendorf J, Robra BP, Wiebelt H, Oberhausen R, Weiland M, Dhom G. Effectiveness of colorectal cancer screening: results from a population-based case-control evaluation in Saarland, Germany. Eur J Cancer Prev. 1993;2:221–7.

The case studies and answers to the following questions on colorectal screening are based on the 1996 recommendations of the United States Preventive Services Task Force (USPSTF), part of the Put Prevention into Practice program of the Agency for Healthcare Research and Quality (AHRQ), formerly the Agency for Health Care Policy and Research. The answers appear on the following page. The evidence on the efficacy of colorectal screening and other USPSTF topics will be reviewed over the next four years; therefore, some of the recommendations may change.

The 1996 recommendations and other information are contained in the “Guide to Clinical Preventive Services,” 2d ed, chapter 8: Screening for Colorectal Cancer. For more information, also consult the “Clinicians Handbook of Preventive Services,” 2d ed, chapter 34: Fecal Occult Blood and chapter 41: Sigmoidoscopy. The guide and handbook can be viewed on the Web site of the AHRQ at http://www.ahrq.gov/clinic. Specific journal references cited in the answers are provided in the discussion.



Copyright © 2000 by the American Academy of Family Physicians.
This content is owned by the AAFP. A person viewing it online may make one printout of the material and may use that printout only for his or her personal, non-commercial reference. This material may not otherwise be downloaded, copied, printed, stored, transmitted or reproduced in any medium, whether now known or later invented, except as authorized in writing by the AAFP. Contact afpserv@aafp.org for copyright questions and/or permission requests.

Want to use this article elsewhere? Get Permissions

More in AFP

Editor's Collections

Related Content

More in Pubmed


May 2022

Access the latest issue of American Family Physician

Read the Issue

Email Alerts

Don't miss a single issue. Sign up for the free AFP email table of contents.

Sign Up Now

Navigate this Article