Colorectal cancer is any cancer that happens in your large intestines, including your colon and your rectum. According to the American Cancer Society, it’s the third-most-common cancer diagnosed in both men and women in the United States.
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In the last few decades, though, the number of colorectal cancer-related deaths has actually been dropping. One reason for that? People are getting regular screenings. As a result, growths known as colorectal polyps are being discovered and removed before they become cancerous.
The most common screening for colorectal cancer is a colonoscopy. However, you may have heard about a noninvasive option called a fecal test, or an at-home test. Colorectal surgeon Arielle Kanters, MD, discusses what these are and who might take them.
How at-home tests work
Screening methods such as a colonoscopy or a CT colonography (virtual colonoscopy) are what are known as visualization tests. “That’s where you can actually see what’s going on inside the colon,” says Dr. Kanters.
As their name implies, at-home tests take place in the comfort of your own home, without a doctor present. But they might not be for the squeamish: These tests are looking for abnormal cells or chemicals present in a sample of your stool (poop) — a sample that you’ll collect yourself.
“The amount of stool depends on the type of test you’re doing,” says Dr. Kanters. “The lab will look [at the sample] for three things — blood products, a breakdown product of blood or abnormal DNA.” That’s cancer DNA, she notes. “If there is cancer in your colon, the cells from that cancer or that tumor will break off and be passed in the stool.”
Unlike preparation for a colonoscopy, which can be intense or uncomfortable, at-home tests are an easier experience. “There’s not much you have to do other than collecting a sample of stool and sending it back to your doctor or directly to a lab,” says Dr. Kanters.
Types of at-home tests
There are three types of at-home colorectal cancer screening tests available.
Fecal occult blood test (FOBT)
With the fecal occult blood test (FOBT), doctors look in your poop sample for blood products. These tests identify the presence of blood using a special substance called guaiac.
Not only is a fecal occult blood test the least sensitive of all of the tests — meaning, it won’t detect as many serious things — but you’ll also have to change your diet for a few days.
“You have to avoid things like red meat,” says Dr. Kanters. “For a few days before, you also can’t take any nonsteroidal anti-inflammatories like ibuprofen.”
Fecal immunochemical test (FIT)
A fecal immunochemical test (FIT) is what’s known as an immunohistochemistry test. This kind of test contains certain antibodies that pick up the presence of blood in your poop.
This test is more sensitive than the fecal occult blood test, and you don’t have to change your diet before taking it.
“But all the test tells you is that there is blood in your stool,” notes Dr. Kanters.
This blood could be from multiple things, she adds. “Maybe you had a bad episode of diarrhea that caused bleeding. Or it could be you have a tumor that is bleeding. In both situations, when you have a bowel movement, some blood will pass in your stool.”
Fecal DNA tests
Fecal DNA tests are a newer kind of test that look for cells with abnormal DNA that might be in your stool.
“When you have cancer in your colon or anywhere in your intestines, some of these cells end up passing in your poop,” says Dr. Kanters.
Fecal DNA tests are the most sensitive of the three tests — meaning, they’re more likely to pick up the presence of cancer. But because fecal DNA tests aren’t visual tests, they can’t pick up the presence of pre-cancerous polyps.
Are at-home tests accurate?
At-home tests are accurate as long as you use them consistently. “You have to be ready and committed to doing it regularly,” says Dr. Kanters. “If you don’t follow the current recommendations for testing, you’re putting yourself at risk of something being missed.”
Fecal occult blood tests and the FIT tests are done annually, she notes. “For the DNA tests, the recommendation for them ranges between one and three years, depending on which guidelines you’re following. You are committing yourself to a much more regular examination.”
Depending on your insurance, the cost of taking a yearly at-home test may also be higher as compared to a single colonoscopy every few years.
How to read the results of at-home tests
You’ll have to wait about two weeks for at-home test results. If your at-home test results do flag something potentially worrisome, don’t panic.
“Talk to your doctor about what the next steps are in terms of figuring out what’s going on,” advises Dr. Kanters.
Needing to have a follow-up visit or test isn’t uncommon. In fact, an at-home test certainly won’t always help you avoid having a colonoscopy.
“If you’re having blood in your poop, your test results are going to be positive and you’re going to need a colonoscopy,” says Dr. Kanters. “If the test is abnormal, you do still need a colonoscopy to follow up and better understand why.”
Relying on at-home fecal tests alone also means that you’re potentially “missing out on an early pre-cancer that could be eliminated and never turn into something scarier,” Dr. Kanters adds.
“One of the benefits of a colonoscopy is that we can not only treat and identify cancers, but we can treat pre-cancers. In other words, the pre-cancerous polyps we might find and remove never reach the point of turning into cancer in the first place.”
Who should take an at-home test?
If you’re looking to have an at-home test done, you can’t just go to the store and buy one. They’re prescription-only, and ordered at the discretion of your doctor.
“It’s important that you have a conversation and figure out if this is the right test for you,” says Dr. Kanter. “These are not for the people who are already having problems. If you’re having new weight loss, if you’re having low blood counts that can’t be explained, if you’re losing blood in your stool — these are all reasons that a full evaluation needs to be performed.”
She adds that at-home tests also aren’t a good option if you have a family history of colorectal cancer or have a medical condition that increases your risk.
An at-home test can be a good choice if you can’t have a colonoscopy because having anesthesia or sedation puts you at higher risk for complications, though.
“With an at-home test, we could at least screen and better understand you’re at risk,” says Dr. Kanters. “Ultimately, the fact that you can undergo a less invasive screening test to at figure out if you need a colonoscopy is fantastic.”
When should you get tested for colorectal cancer?
If you are at average risk for colorectal cancer — that is, you have no existing symptoms, family history or risk factors — your first colonoscopy should happen at the age of 45. That’s also the age you’d start doing at-home tests, says Dr. Kanters.
Still, you need to have a conversation with your doctor before going this route. “These are for the perfectly healthy 45-year-old with no family history,” she says. “Those are the right candidates for at-home tests.”
Although she always recommends having a full colonoscopy so doctors can catch more potential problems, getting some kind of colorectal cancer screening is always better than avoiding them entirely.
“Ultimately, if this is going to be the thing that gets you in to be screened for cancer, absolutely do this,” Dr. Kanters says. “If you feel strongly that you will not undergo a colonoscopy, please ask your doctor about at-home tests. They’re a great way to determine if something else needs to be done and better understand your risk for possibly having cancer.”
To learn more from Dr. Kanters about the importance of colorectal cancer screenings, listen to our Health Essentials Podcast episode, “Colorectal Cancer Screening Options.” New episodes of the Health Essentials Podcast publish every Wednesday.