Home screening options for colorectal cancer

photo of tube and swab used for a fecal immunochemical test

Among the many things the pandemic has taught us, it's that we can do more from home when it comes to our medical care — whether it's getting a check-up via video or phone call (telemedicine) or sending blood pressure measurements to doctors electronically.

For some people, it's also meant trying an at-home screening test for colorectal cancer. These tests have been approved for years, but are often passed over in favor of colonoscopies (see "The gold standard in colorectal cancer screening").

Now, however, there's a huge backlog for colonoscopies because so many people had to cancel their appointments during the pandemic. "We'll never catch up with all the colonoscopies that have to be done. So for people at average risk of colorectal cancer, it's reasonable to use an alternative screening method," notes gastroenterologist Dr. Lawrence S. Friedman, a Harvard Medical School professor and the Anton R. Fried, M.D., Chair of the Department of Medicine at Newton-Wellesley Hospital.

On the other hand, people who have symptoms that could be caused by colorectal cancer, or who are at increased risk for it — because colorectal cancer runs in their family or because they have conditions such as inflammatory bowel disease — should still have regular colonoscopies.

The gold standard in colorectal cancer screening

The most comprehensive colorectal cancer screening test is a colonoscopy — a procedure that enables the doctor to examine the inside of your colon and to snip out suspicious growths.

Before the procedure, you drink liquids that help you clean out your colon so the doctor can see everything. The doctor then passes a long, flexible tube into your colon; the tube carries a tiny video camera and surgical instruments.

The process is lengthy and sometimes unpleasant, but it's worth it. "Colonoscopy is the most sensitive test available for identifying colon cancer; it detects at least 95% of cancers. And when you remove a potentially precancerous polyp, you're preventing a future cancer," explains gastroenterologist and Harvard Medical School professor Dr. Lawrence S. Friedman.

A screening colonoscopy is recommended at age 45, and every 10 years thereafter if no polyps are found (until age 75), or more often if there's an increased risk of colorectal cancer.

What are the tests?

An at-home screening test is a kit that allows you to collect a stool sample in the privacy of your home. The collection process is quick and easy, and it requires no bowel preparation.

The stool sample is sent to either your doctor's office or a lab. There, it's analyzed for signs of colorectal cancer, such as microscopic amounts of blood (which can come from tumors or precancerous growths called polyps) or DNA from cancer cells.

Three types of at-home screening tests are recommended by the U.S. Preventive Services Task Force:

A guaiac fecal occult blood test (gFOBT) uses chemicals to find blood in the stool. This test must be done once a year.
A fecal immunochemical test (FIT) uses antibodies to detect blood in stool. It must be done once a year.
A multitarget stool DNA (mt-sDNA) test (Cologuard), also known as a FIT-DNA test, can identify DNA from cancer cells in the stool and has a FIT component to look for blood. This test must be done every three years.

Costs and availability

Your doctor typically prescribes an at-home screening test, and Medicare pays for it if you don't have any symptoms of colorectal cancer.

People who don't have a doctor can go online and order a FIT-DNA test (at www.cologuard.com), and the test maker will arrange for a telemedicine visit with a physician who will evaluate you and then can prescribe the test. But you'll probably have to pay for the telemedicine visit.

You can buy some gFOBT or FIT tests online or over the counter for $10 to $25, but these tests may not be as accurate as the kinds prescribed by a physician. In any case, you should discuss your test results with a doctor.

Test accuracy

At-home screening tests differ in their ability to detect colorectal cancer. "The FIT-DNA is the most sensitive. It finds cancer, when present, about 92% of the time. FIT tests find cancer 80% to 82% of the time," Dr. Friedman says. "The gFOBT test is less sensitive, identifying between 20% and 50% of cancers, and has fallen by the wayside."

Sometimes at-home test results are falsely positive, responding to bleeding from other types of polyps or abnormalities in blood vessels. That can happen about 14% of the time with FIT-DNA tests and about 5% of the time with FIT tests. "But remember that at-home tests suggest you might have colorectal cancer. To diagnose the cancer requires a colonoscopy" Dr. Friedman says.

What happens next?

If you have a positive at-home test result, you'll need to see a gastroenterologist for a follow-up colonoscopy to locate and remove tumors or precancerous polyps. If you have a negative at-home test result, you should (as always) continue to watch for potential signs of colon cancer, such as:

a feeling that the bowel isn't emptying completely
blood in the stool
stools that are narrower than usual
frequently feeling full or bloated
weight loss with no known reason.

"If you develop any of those symptoms, you may need a colonoscopy for evaluation," Dr. Friedman says. "If you don't have any symptoms, and you're at average risk for colorectal cancer, you'll still need to keep up with at-home testing every one to three years."

Colorectal cancer can be cured if it is caught early with a screening test. But don't put off a screening because you're not sure which one to get. As Dr. Friedman puts it, "The best screening test is the one that gets done."