Fecal Occult Blood Tests Reduce Colorectal Cancer Mortality
Should physicians use fecal occult blood testing to screen for colorectal cancer?
Fecal occult blood testing reduces colorectal cancer mortality by 16 percent. Annual testing and rehydration of samples increases testing sensitivity but also increases the number of false-positive results.
Colorectal cancer is the third most common cancer in the United States, affecting 46 out of 10,000 women and 63 out of 10,000 men. U.S. Preventive Services Task Force and American Cancer Society guidelines recommend multiple options for screening average-risk patients. These options include annual fecal occult blood testing, flexible sigmoidoscopy, home fecal occult blood testing plus flexible sigmoidoscopy, colonoscopy, and double-contrast barium enema.1,2 Average-risk patients are those with no history of rectal bleeding, adenomatous polyps of the colon, or inflammatory bowel disease. There are specific screening guidelines for patients who have a family history of colorectal cancer or genetic cancer syndromes. Most higher-risk patients require a colonoscopy for initial screening.2
This Cochrane review included four randomized controlled trials (329,642 total patients) of fecal occult blood testing to screen for colorectal cancer. Outcomes included test sensitivity and reduction in all-cause and colorectal cancer mortality.
The review showed that fecal occult blood testing reduces colorectal cancer mortality by 16 percent (relative risk = 0.84; 95% confidence interval [CI], 0.78 to 0.90). Rates of patient compliance to testing ranged from 59 to 75 percent. Test sensitivity was highest in rehydrated samples, with 82 to 92 percent sensitivity for colorectal cancer or adenoma. Nonrehydrated samples had a sensitivity of 55 to 57 percent. Colorectal cancers were also detected earlier in the screening group. The positive predictive value of the fecal occult blood test (percentage of patients with a positive test who actually had cancer) ranged from 0.9 to 18.7 percent. Fecal occult blood testing did not reduce all-cause mortality.
Fecal occult blood testing is a cost-effective, noninvasive screening method for colon cancer. Although endoscopy has higher specificity for colorectal cancer, screening recommendations for colonoscopy and flexible sigmoidoscopy are based on case-control studies. In fact, there is no direct evidence that endoscopic screening reduces all-cause or colorectal cancer mortality.1 These tests also require more patient preparation and have a higher risk. Fecal occult blood testing remains a good screening option for average-risk, compliant patients.