When to use an at-home colorectal cancer screening test instead of a colonoscopy

Credit: Justine Ross/Michigan Medicine.

Colorectal cancer, or collectively, cancers that develop in the colon and/or rectum, are currently on the rise.

The United States Preventive Services Task Force recommends that adults begin screening for colorectal cancer at the age of 45.

But when should someone use an at-home colorectal cancer screening test versus scheduling a traditional colonoscopy?

Elena Stoffel, M.D., M.P.H., director of cancer genetics at the University of Michigan Rogel Cancer Center, recently spoke to Health Lab about at-home stool tests and when to use them.

How would you describe these at-home screening tests? 

Stoffel: I think it’s important to remember that colonoscopies are still the gold standard when it comes to colon cancer screening. Colonoscopies are the only test approved for screening patients that are at a higher-than-average risk for colorectal cancer.

Currently, there are other non-invasive tests available, but they are only approved for individuals who are at average risk for colorectal cancer.

These tests can be ordered by the patient or their provider(s) and involve securely sending a stool sample to a testing facility.

If someone then tests positive on a stool-based colorectal cancer screening test, it is recommended that they undergo a colonoscopy.

These non-invasive tests have evolved over time. How accurate are they? 

Stoffel: The non-invasive tests that are looking for blood in the stool are referred to as fecal immunochemical tests, or FIT tests. Essentially, they use antibodies to detect blood in the stool.

There are other non-invasive stool tests, like Cologuard, which detect blood in the stool, as well as DNA markers that have been found in colorectal cancer tumors.

The old stool-based colorectal cancer screening tests that were used in the early 1990s were not nearly as good as today’s FIT tests.

The sensitivities surrounding these newer tests give them about an 80% accuracy rate for detecting colorectal cancers.

The FIT test is good for detecting colorectal cancer, but not for identifying polyps.

This is very important to remember, especially if you’re hoping to prevent colorectal cancers by detecting and removing pre-cancerous polyps. In this case, you’ll need a colonoscopy.

Who are these non-invasive tests for, in particular? 

Stoffel: The non-invasive colorectal cancer screening tests are really designed for asymptomatic individuals who are at average risk for developing colorectal cancer.

Anyone who has colorectal cancer symptoms, a family history of colorectal cancer (i.e., a first degree relative with colorectal cancer) or has had one or more large pre-cancerous polyps (from things like inflammatory bowel disease, Crohn’s disease and other gastroenterological conditions) should have a colonoscopy, rather than a non-invasive screening test.

Another thing that is important to note is that non-invasive stool-based colorectal cancer screening tests should be repeated every one to three years, whereas a normal colonoscopy screening test can protect against colon cancer for about 10 years.

And if colon polyps are removed before they become cancerous, most cases of colorectal cancer can be prevented.

Therefore, colonoscopies are not merely a colon cancer detection test, they are also a colon cancer prevention test. Many at-home, non-invasive tests are good at detecting cancer, but not preventing it.

Is there anything important related to these screening modalities people should know? 

Stoffel: There’s a lot in the news today about new blood tests for detecting cancers. While the technologies are exciting, they’re far from perfect. There can be false negatives and false positives.

Some of the laboratories involved in developing these tests have algorithms to determine if a positive blood-based cancer test corresponds to a colorectal cancer (versus another type of cancer), but one of the downsides of this process is figuring out what the next steps are.

If a blood test comes back positive, should a patient get a colonoscopy or a CT scan first? And if the colonoscopy is negative, what additional testing is required to rule out other cancer types?

The NIH is conducting studies to examine the risks and benefits of these new blood tests for cancer detection.

Ultimately, our goal is to help get as many people screened for colorectal cancer as possible.

So, individuals that are age 45 and older who are of average risk of developing colorectal cancer are encouraged to consider these non-invasive screening tests.

Meanwhile, those who are deemed to be at higher-than-average risk for colorectal cancer or who test positive on a non-invasive test should make their colonoscopy appointments sooner.

If you care about colon cancer, please read studies that common high blood pressure drugs may lower colon cancer risk, and findings of common vegetable that may help lower your cancer risk.

For more information about health, please see recent studies about low-carb diet could increase overall cancer risk, and results showing that high vitamin D levels linked to decreased risk of bladder cancer.