Rates of colorectal cancer screening.

We recently reported that 23.5% of Canadians aged 50 years or older who were at average risk for colorectal cancer had ever received screening for colorectal cancer; this value fell to 17.6% when only up-to-date screening was considered. In the CMAJ editorial published with our study, Alan Barkun and Ken Flegel reported that 62.9% of patients in the United States were screened. Roy Preshaw subsequently expressed concern that the US screening rate reported by Barkun and Flegel was exaggerated; the editorialists defended their position. Although the rate of colorectal cancer screening may be higher in the United States than in Canada, Preshaw correctly pointed out that the rate reported by Barkun and Flegel was overstated. However, the explanation for the inflated US rate is probably not recall bias, as Preshaw postulated. As confirmed by the lead author of the US study in question, the rate cited by Barkun and Flegel was for patients who received fecal occult blood testing, sigmoidoscopy or colonoscopy for any reason (not only for screening) (Dr. Neeraja B. Peterson, Center for Health Services Research, Vanderbilt University Medical Center, Nashville, Tenn.: personal communication, 2008) and thus reflects the rate of testing for patients who were “ever tested,” not “ever screened.” Previous US survey studies also suffer from this limitation. The impact of this misinterpretation is obvious when one considers that 40% of endoscopic tests and 11% of fecal occult blood tests are performed for purposes other than screening. Another reason to question the quoted US screening rate relates to the risk of cancer in the study population. In contrast to our Canadian study, which surveyed people at average risk, US studies included people with a family history of colorectal cancer and people with inflammatory bowel disease. Inclusion of such patients would modestly increase the perceived rate of screening. How do colorectal cancer screening rates in Canada compare with those in the United States? We found that in 2003, 12% of Canadians reported undergoing fecal occult blood testing for screening according to published guidelines and 8% reported undergoing sigmoidoscopy or colonoscopy for this purpose. The comparable rates for US residents in 2000 were 15% and 21%. Although the rates of colorectal cancer screening appear to be higher south of our border, the actual differences between the 2 countries are less then they appear. Colorectal cancer screening in both countries remains inadequate and should be actively promoted to reduce preventable deaths from colon cancer.