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What to know about at-home tests for colorectal cancers

The only real downside to the two popular stool tests is that they need to be done more often than a colonoscopy, experts say.

If you’ve been putting off a colon cancer screening because you’re nervous about getting a colonoscopy, there’s a less invasive option worth considering: at home stool testing.

The only real downside to the two most popular stool tests, the fecal immunochemical test (FIT) and the stool DNA test (Cologuard), is that they need to be done more often than a colonoscopy, experts say. And, OK, it’s also possible that some folks might be put off by the ick factor of getting that close to one’s stool.

For those with no symptoms or family history of colon cancer, the U.S. Preventative Services Task Force in 2020 recommended screening start at age 45. Screening colonoscopies only need to be done once every 10 years, for people who do not have other risk factors and no sign of cancer during a colonoscopy. The at-home options need to be done more frequently: FIT is a yearly test and Cologuard is should be performed once every three years.

“I think that FIT, and for that matter Cologuard, are appropriate for people who would prefer to avoid a colonoscopy,” said Dr. Otis Brawley, a professor of oncology and epidemiology at the Johns Hopkins School of Medicine and the Johns Hopkins Bloomberg School of Public Health in Baltimore. “However, people should realize that if they have a positive test they should get a colonoscopy.”

How at-home tests work:

The tests analyze the stool for signs of blood, which can signal the presence of cancerous lesions or polyps. There are not drug or dietary restrictions to take before doing either test, according to the American Cancer Society. A health care professional will provide you with the supplies you need and detailed instructions to follow.

Once a person has a positive stool test, then a follow-up colonoscopy has to be done to seek out and remove cancerous and precancerous lesions.

An advantage of stool tests is they have the best scientific evidence showing they reduce cancer deaths, Brawley said. “They’re the gold standard,” he added. Though the American Cancer Society notes that they can miss many polyps and some cancers, and some tests could lead to false-positive results. This is why FIT tests are recommended to be taken every year. Over the course of several years it's assumed that no cancers will be missed. False positives are only a problem in that a colonoscopy is needed to determine whether the person has cancer or not.

Stool-based tests vs. colonoscopies

The stool tests come with no real risks of harm to the body. That’s compared to a colonoscopy, which does come with rare, but real, risks, such as a nicked bowel. In the Medicare population, for which there is good nationwide data, it’s been shown that nicked bowels occur in 1 out of every 600 colonoscopies, Brawley said. “But most of those people do not need anything other than to be sent home with a restricted diet for a few days, rarely more than four or five.”

Occasionally, however, the nick is severe enough for bowel contents to leak into the abdomen, which can cause a serious infection called peritonitis.

One other negative for some people is the bowel prep that needs to be done before a colonoscopy to clean everything out of the colon and rectum so the doctor can see any lesions clearly. Sedation is also usually required, which can cause someone to miss a day of work. While a colonoscopy can usually review the entire colon, it still could miss small polyps.

It’s estimated that among Americans recommended for routine screening for colon cancer, about a third are not getting the recommended testing — some of them might be more likely to get tested if screening were easier and could be performed conveniently at home.

A 2021 study found that screening rates jumped by more than 1,000% when researchers sent take-at-home tests to patients who were overdue.

The results might have been even better during the pandemic since some people might be hesitant to come into a medical center for a colonoscopy, said study co-author Dr. Shivan Mehta, an assistant professor of medicine at the University of Pennsylvania’s Perelman School of Medicine and an associate chief innovation officer at Penn Medicine in Philadelphia.

“The FIT test has been around for a very long time,” Mehta said. “It’s a lot easier to do than a colonoscopy. But in order to have similar effectiveness to colonoscopies, it has to be done every year. Both have pros and cons. Ultimately, the best test is the one that someone completes.”

The FIT test looks for human hemoglobin in the stool, Brawley explained. Hemoglobin is a marker for blood in the stool, which can be symptom of colon cancer. That’s why positive FIT or stool DNA tests necessitate a colonoscopy.

There is yet another option for folks who want to avoid a colonoscopy but want to have a screening test that they will need only once every 10 years, Brawley said. That’s a virtual colonoscopy done with a CT scanner, he explained.