Colonoscopies are considered the gold standard for detecting colorectal cancer.
But some dread the idea of the invasive procedure and the prep required the day before you have it.
The FDA last year approved at-home blood and stool tests for the disease, but are they a match for colonoscopies?
KERA’s Sam Baker talked about this with Dr. Amit Desai, a gastroenterologist with Texas Health Presbyterian Dallas.
Desai: The basic FIT (Fecal Immunochemical Test) test actually tests for human blood in the stool. And if it meets a certain amount of human blood in the stool, it flips positive.
The multi-targeted stool DNA test, Cologuard, also tests blood in the stool. But it also tests for specific forms of DNA associated with colon cancer and advanced polyps. If either of those test positive, it's recommended that patient get a colonoscopy.
The blood test, which is the Shield test, tends to be better at identifying cancer itself. So, if that test is positive, it's more commonly in patients who may already have cancer. The sensitivity of that test is about 13% for polyps or advanced polyps. So it's not as good at looking at polyps. But that is performed with just a simple blood test. And again, if that turns positive, that patient absolutely should get a colonoscopy.
Baker: Can they (the tests) confirm colorectal cancer? Or do they merely suggest the possibility of it?
Desai: These tests are generally pretty good identifying cancer. But remember, colon cancer is a potentially preventable cancer. We want to identify those patients who have high risk lesions like polyps or advanced polyps before they get cancer. Fit and Cologuard, which are those stool tests, are okay at picking up polyps. They're still not perfect at picking up polyps or advanced polyps. They're pretty good at identifying cancer. And that's similarly with the blood test as well.
The blood test is decent at picking up cancer. But be careful because only about 83% in that big study of patients and you look at the sensitivity of that test flipped positive when they looked for those patients who had cancer.
The sensitivity of a test tells you that how comfortable you can be to trust that test is negative. So, if you get a shield test or the blood test done in that test comes back negative. You're comfortable about 83% of the time. That also means 17% of the time you're not comfortable. You could have cancer. And that test came back negative. So you have to keep that in context.
When you look at the overall picture, here is our goal for this is to prevent cancer. And if your shield test is positive, it's pretty good at picking up cancer. But we may be too late at that point.
Baker: These tests don't replace or can't replace colonoscopies?
Desai: The ideal and best test overall is a colonoscopy because we can find polyps or adenomas and remove them from a patient to prevent that patient from ever getting cancer itself.
Baker: Then is the advantage of the fit and shield test that maybe it might encourage more people to screen for colon cancer?
Desai: It's for those patients who, A, can't do a colonoscopy or won't do a colonoscopy. B, there's it's not easy to do a stool test either. You know, it's not fun testing when we go test my stool and send it off. And so at least something is getting done because you're starting to catch people who aren't able to get a colonoscopy, aren’t able to do the stool test, they're doing something. And if those patients, those turn positive, they're then getting their colonoscopy.
I want to stress that colon cancer is a potentially preventable, treatable, curable cancer. So, if with colonoscopy, we can prevent if with the stool test and colonoscopy combined, we if let's say we do find cancer, we can if it's early stage, we can treat and cure cancer. So, you know, it's over 45. Getting a test done is the most important thing for that individual.
Baker: In the meantime, before you even get to that point, what are things that people should do to try to prevent colon cancer?
Desai: We know smoking is a big thing. And now we're starting to see some recent literature. Actually, within the last week, the surgeon general put up a little flag on alcohol. So, we know smoking and alcohol contribute to that. So, I think those are obvious things.
We know in the grand scheme of things of cancer in general. There's also been some implication that obesity and a sedentary lifestyle may play a role in the development of polyps and cancer, and that when we look at a diet standpoint, heavily processed, ultra processed diets, processed meats, also play a role in development of colon cancer.
And then we also know that eating more fruits and vegetables, eating even more fish, actually has a protective effect and a more active lifestyle has a protective effect. So, when we think about all these factors, there's a lot of that I think many of us already know. If we encourage those things into our lifestyle, we see those patients tend to have a lower rate of polyp formation and the lower rate of colon cancer. But it's not perfect.
So if you're healthy, you know, work out all the time active, good BMI, eat perfectly. There's still a percent of those patients who are developing colon cancer. So, in addition to lifestyle, that's why these screening tests exist. Colonoscopy exists. Because no matter what you do, there's still a chance that you can develop colon cancer in your lifetime. And so getting that initial colonoscopy when you're 45 is really the next step of prevention.
Baker: In the meantime, if you want to opt for the other tests, at what point should you begin doing that?
Desai: 45 for the other tests as well. Keep in mind, if you have high risk family history, a first degree relative with colon cancer, a first degree relative with a ton of polyps that has to keep going back for the colonoscopy. The only test you can do is a colonoscopy. You should not do one of these other tests. But otherwise, the first time these other tests should be done is the age of 45.
RESOURCES:
- Colonoscopy vs. at-home colon cancer screening: Which is best for you?
- Colon cancer screening: Weighing the options
Copyright 2025 KERA