How Does Colonoscopy Compare with Fecal Occult Blood Testing as a Screening Tool for Colon Cancer?

Document Type


Publication Date



A Cochrane review conducted a meta-analysis looking only at FOBT for colorectal cancer screening. This review, based on published and unpublished data from 5 controlled trials, demonstrated that 3-card home FOBT conferred a reduction in colorectal cancer mortality of 16% (relative risk [RR]=0.84; 95% confidence interval [CI], 0.77-0.92) and a number needed to screen of 1173 (95% CI, 741-2807) to prevent 1 death from colon cancer over a 10-year period. If adjusted for adherence to screening, the reduction in mortality increased to 23% (RR=0.77; 95% CI, 0.57-0.89). In addition, long-term follow up of one of the RCTs in the review showed a continued reduction in colorectal cancer mortality of 34% (RR=0.66; 95% CI, 0.54-0.81) in subjects adhering to the FOBT screening protocol over a 13-year interval. Overall mortality did not differ between the screened and unscreened groups. A systematic review performed for the US Preventive Services Task Force (USPSTF) incorporated more recent data on colorectal cancer screening including colonoscopy. This review reached similar conclusions as above. This review also looked at office FOBT performed after digital rectal exam. It is important to note that a single office FOBT has a lower sensitivity than 3-card home FOBT and its effectiveness for reducing colorectal cancer mortality was unknown at the time of the systematic review. A subsequent 2005 Veterans Affairs prospective cohort study found that the sensitivity for detecting advanced neoplasia was only 4.9% for digital FOBT, and negative results did not decrease the likelihood of advanced neoplasia. The USPSTF review did not find any screening trials of colonoscopy but analyzed data from the National Polyp Study and a case-control study to draw its conclusions. The review reported an odds ratio for colorectal cancer mortality for patients who had colonoscopy to be 0.43 (95% CI, 0.30-63). The USPSTF review also looked at the sensitivity and adverse effects of FOBT compared to colonoscopy. One-time 3-card home FOBT had a sensitivity of 30% to 40% for detecting cancer. The sensitivity of one-time colonoscopy was difficult to determine since it was the criterion standard examination, but it was estimated to be greater than 90%, with a risk of perforation of 1/2000. The USPSTF review found both screening strategies cost-effective (<$30,000 per additional life-year gained) compared to no screening. FOBT had a cost per life-year saved of $5691 to $17,805 compared with $9038 to $22,012 for colonoscopy performed every 10 years.