Colonoscopy vs. Stool-Based Tests: What is the Best Way to Detect Colorectal Cancer? 

Generally speaking, how do colorectal screening tests work?

There's a whole menu of options for colorectal cancer screening and prevention that we offer our patients, and though each one has its advantages and disadvantages, they are equally recommended by our professional societies, including the U.S. Preventive Services Task Force, the U.S. Multi Society Task Force on Colorectal Cancer, and the National Comprehensive Cancer Network. 

We divide the screening options into two major categories. One is structural tests, which includes colonoscopy, flexible sigmoidoscopy, and CT colonography. These are tests that give us a structural examination of the colon and rectum. With a colonoscopy, you can visualize the entire colorectum and screen and detect cancer before it's causing symptoms, but you also can potentially remove precancerous polyps to prevent cancer.  

The other category is stool-based tests. These tests essentially take advantage of what a precancerous polyp or cancer could be shedding into the stool and try to detect those markers in the stool as a heads-up for a possible cancer.  

How many stool-based tests are there, and how do they work?

The two main stool tests are fecal immunochemical testing, or FIT testing, and FIT fecal DNA testing. The FIT test, essentially, is looking for microscopic blood. Blood in the stool can happen for a variety of reasons, such as hemorrhoids or irritation, but it also can be an indicator of more serious things, like precancerous polyps or colorectal cancer.  

The FIT fecal DNA test, which is commercially marketed as Cologuard, is a FIT test with added DNA markers that have been associated with polyps or cancers.  

The stool tests are considered two-step tests, meaning if you get this type of test, it doesn’t tell you whether you have cancer or not. If the results of a stool test are abnormal, it requires a colonoscopy to diagnose what's going on. The colonoscopy confirms whether or not there's a polyp that might be precancerous, or even if there’s cancer. The colonoscopy is important because at that time, tissue samples can be taken, the site can be marked, and it advances the patient's treatment. The stool-based tests, on their own, have to be paired with a colonoscopy to be effective if the result is abnormal.  

How do the FIT tests work?

It's a kit that your doctor either can mail to you or send you home with after a visit, and you complete everything in the privacy of your home. It comes with full instructions, and it requires a stool sample that you submit in the packaging and the materials that come in the kit and mail it back. It’s all very sanitary, they provide everything you need to do it, and they make it as easy as possible. You don’t need to make any medication or dietary changes, and no bowel preparation is required. 

Which test is better, colonoscopy, FIT, or FIT fecal DNA?

Patients always ask us that question. The overwhelming message is that the best test is the test that gets done. For patients between the ages of 50 and 55, only about 50% are up to date on colon cancer screening. And that's for a variety of reasons. Oftentimes these are folks who are full-time employees, and it's hard to take time away from life, family, or work obligations to get a colonoscopy. There also are certain barriers to colonoscopy, such as transportation, preparation, or patients who just don't want an invasive test.  

It's important, when you're choosing which test to do, to pick the one you're actually going to do, and to pick the one where the risks and benefits fit your personal preferences. The stool-based tests are an outstanding option for that 50% of patients who are not up to date on screening and want a noninvasive option, as long as they understand that if the results are abnormal, it will require them to carve out the time to get that follow-up colonoscopy to close the loop.  

What is the timing on these tests? How often do you need them?

With the FIT test alone, that's a test we recommend being done annually. That can be paired with other blood tests or other testing that patients get done from their primary care doctor. The FIT fecal DNA test currently is recommended to be done every three years. And a colonoscopy is recommended every 10 years.  

Are they all covered by insurance? What if you get an abnormal result on a FIT test and have to get a follow-up colonoscopy?

Under the Affordable Care Act, any grade A or grade B recommendation from the United States Preventive Services Task Force is required to be covered by insurance or payers at no cost to the patient. It can't require copayment, and it doesn't go toward a patient's deductible. Colorectal cancer screening for those ages 45 and older is a grade A and B recommendation. So all of these tests should be covered by insurance, and that should not be a barrier. There was some confusion a few years back about the FIT test — if the initial results of a FIT test are abnormal, will the follow-up colonoscopy be covered? The Biden administration last year clarified that insurance covers completion of the screening process, and both steps are mandated to be covered. That follow-up colonoscopy is not considered a new diagnostic test; it is considered completion of screening.  

How accurate is each type of test in detecting cancer?

No test in medicine is perfect, but if we take 10 patients who have a known colorectal cancer, the FIT test will pick up eight out of 10. It has 80% sensitivity. But remember, this is an annual test. So if it's an early-stage cancer, it's unlikely to progress very quickly. If the patient is able to get that every year, there is a high likelihood of the cancer being detected at a curable stage in subsequent years. The sensitivity for FIT fecal DNA is 92% — it will pick up nine out of 10 cancers — and colonoscopies are more than 99% accurate.  

Colonoscopies have the advantage of being able to remove polyps during the screening test itself. How important is that?

It's incredibly important, and that's why it’s really the standard of care. The colonoscopy allows a good, careful examination, but the effectiveness of the procedure is in removing the polyps. Most polyps can be removed during the same procedure, the same day, and it's very safe. Occasionally, depending on how young or old the patient is, we will find larger polyps in 5% to 10% of patients. In that scenario, it might not be the right time, or we may not have the right equipment or team to make the call during the routine colonoscopy, but we've diagnosed it, and we can mark that and then bring the patient back for a more extended procedure to follow up about what's going on. 

How common is colorectal cancer?

Colorectal cancer is the third most common cancer diagnosed in the United States, but it’s the second leading cause of cancer-related death. Because of screening, we've seen the rates of colorectal cancer decrease in those who are eligible for screening. But depending on the age group, we have a long way to go to getting the entire eligible population screened. What's really alarming is that we've seen the rates of colorectal cancer in younger individuals, those under the age of 50, starting to go up over the past several decades. And though we don't fully understand why that is, it's a large push behind why all of the professional societies over the last few years have updated our screening guidelines to start the age of screening at 45 instead of 50, which is where it's been since the 1990s.  

Colorectal cancer is not a disease of the old; it can happen at any age. The best time to talk to your doctor about colorectal cancer risk is when you meet them. At that time, it is important to review family history of colorectal cancer or colorectal polyps, as well as symptoms such as rectal bleeding. These factors may influence when your doctor recommends testing. In the absence of family history and symptoms, all patients should be getting screening at age 45.