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Screening with FIT or Colonoscopy - Which is Best for Me? Photo by Rohan Makhecha on Unsplash

Screening with FIT or Colonoscopy - Which is Best for Me?

Ontario now offers the Fecal Immunohistochemistry Test, or FIT for short, as an option for colorectal cancer screening in average risk individuals. People who are at higher risk need to consider colonoscopy as their primary screening test. The FIT is a single-sample stool test that checks for minute amounts of blood in the stool.

If you are at the age where it is necessary to consider your colorectal cancer screening options, what should you do?

The answer is that you should do something. Any screening test is better than no screening test.

The Ontario Medical Association section of General Surgery and section of Gastroenterology (who represent these medical specialists in Ontario), the American Gastroenterological Association and the U.S. Preventive Services Task Force support colonoscopy for screening as the preferred test rather than the FIT.

Politically, this is interesting. Surgeons and gastroenterologists prefer colonoscopy. The government agency, Cancer Care Ontario recommends the FIT. If you're the patient, the decision is yours to make. Here is a detailed open letter giving the surgeons' and gastroenterologists' view on the question called "FIT testing: a reality check for family physicians".

Switching sides in the discussion, the biggest benefit of the FIT is that it is a single stool sample, provided once every two years. The test gives a numerical value as to how much blood is present in the stool. If that value exceeds a threshold that is set according to the probability of having cancer, and according to the resources available to fund colonoscopy procedures, then a follow-up colonoscopy will be suggested.

What is the difference in detecting cancer or near-cancerous lesions if one compares a colonoscopy once every 10 years to a FIT once every two years?

To address that question, Grobbee and colleagues in Clin Gastroenterol Hepatol. 2019 Aug 13., looked at 30,007 patients of screening-age in the Netherlands. They were divided into three groups. 15,046 people were invited for 4 rounds of the FIT test by mail, 8,407 people were invited for a flexible sigmoidoscopy (that can be considered as a colonoscopy that plans to see only about half of the colon), and 6,600 people were invited for colonoscopy. In the group that was invited to have FIT screening, 77% of people agreed to participate. Of the group that was offered colonoscopy, 24% took part. Results showed that using an 'intention to treat' analysis, the FIT screening found advanced neoplasia (cancer or lesions at higher risk to turn in to cancer) in 4.5% of invitees (the 15,046), and colonoscopy found advanced neoplasia in just 2.2% of the invitees. Hence, one could conclude that the FIT is better. Indeed, at a population level, the authors conclude that the FIT test is a great screening option. However, when the researchers did an as-screened analysis, the yield of advanced neoplasia with colonoscopy was 9.1%, compared to 6.1% for the FIT group.  The difference being that the as-screened test considers as the denominator the number of tests performed, whereas the intention to treat analysis considers as the denominator the number of people invited, regardless of whether or not they decided to participate in any testing. In other words, when given the choice, more people will opt for the stool test than for colonoscopy. But for those people who want the best medical result and are prepared to submit to a more invasive test, the protection they receive against colon cancer is significantly better with colonoscopy.

The bottom line: colonoscopy found about 50% more advanced lesions such as cancers or lesions at risk of becoming cancer, than four iterations of the FIT test (9.1% vs. 6.1%). Still, consider the important observation by Drs. Vinden and Murray in their letter: "FIT aficionados state that the "Programmatic Sensitivity" of FIT is in the 80% range. This is the dubious concept of "sensitivity with repeated testing": you may miss it the first, second, third, or fouth time, but hopefully you'll catch it before it becomes clinically apparent -- and then declare it a success for the screening program. No other test presents its accuracy in such a distorted fashion. For many patients the potential benefits of early detection will have been squandered."

Ultimately the best test for you comes down to your comfort level with the two options.  FIT is easy and gives what may doctors consider acceptable protection; colonoscopy is more involved and gives  better, arguably, the best available protection. The only bad option is to choose to do nothing.

Author: Mark Reimer, MD MBA BSc FRCSC
Medical Director of The Reimer Clinic and director in Freiheit Care Inc., premium home care services.