At-Home Screening Tests for Colon Cancer

Written by Kim Painter
Medically Reviewed by Shruthi N, MD on October 16, 2024
12 min read

The gold standard screening test for cancer in your colon or rectum, colorectal cancer, is a colonoscopy. This is done at a doctor's office under sedation, after a day of preparation that involves fasting and clearing out your bowels. But there are alternatives: tests you take at home by collecting samples of your poop and sending them to a lab. These tests have been around for a while but have become more widely used in recent years.

Home tests are easier and quicker and can be a good choice for people who can't or would rather not have colonoscopies. They're safe and effective, but there are trade-offs you should consider when choosing the best method for you.

 

 

 

 

 

 

There are three major types of at-home colon cancer tests. All involve collecting stool samples, but there are differences in how they work and how often you need to do them to effectively screen for signs of colorectal cancer.

Guaiac fecal occult blood test (gFOBT)

This test uses a chemical to look for hidden (occult) blood in your stool, which can be a sign of colorectal cancer. You have to do it every year. Unlike other home tests, the gFOBT requires you to collect more than one poop sample. And because certain drugs and foods can affect the results, you have to avoid them for several days before testing. It's less widely used than other home methods.

Fecal immunochemical test (FIT)

This test also looks for small amounts of hidden blood in your poop, using antibodies, which are special proteins that can recognize and bind to particular substances — in this case, a blood protein called hemoglobin. It can usually be done with one stool sample and doesn't require you to change your diet or medications beforehand. You need to repeat it yearly.

Multitarget stool DNA test (Cologuard)

This combines testing for blood with testing for DNA or gene changes in cells that can get into your poop from polyps (precancerous growths) or cancers. It's repeated every 3 years. The only FDA-approved version of this test is sold as Cologuard.

Guidelines from major medical groups in the U.S. say that people at average risk for colon cancer should start screening for the disease at age 45 and continue it until at least age 75. Some people might continue after age 75. The guidelines say everyone should talk to their doctors about the best screening methods for them and that home tests can be acceptable alternatives for many people.

At-home testing might be a good choice if you can't get time off work for the colonoscopy prep and procedure, if you fear sedation, or if you have medical problems that put you at higher risk of complications from sedatives or anesthetic drugs. Studies show that having the option of home testing leads more people to get tested.

But the guidelines differ if you are at higher-than-average risk for colon cancer. In some cases, you'll need to start screening at an earlier age, get screened more often, and stick to colonoscopy, which allows your doctor to examine your colon directly and remove polyps. While most polyps are harmless, a small number turn into cancer, so finding and removing them is a way of preventing cancer.

You are at higher-than-average risk if you have:

  • A family history of colorectal cancer, certain kinds of polyps, or genetic conditions that raise colon cancer risk
  • A previous diagnosis of colon cancer of precancerous polyps
  • A disease of the colon or rectum, such as ulcerative colitis or Crohn’s disease

Note: In place of colonoscopy or home stool tests, some people might consider two other visual exams of their colon and rectum, typically recommended every 5 years:

  • A virtual colonoscopy in which you get a CT scan of your colon and rectum, with no sedation, but the same bowel-cleaning preparation used in a regular colonoscopy
  • Flexible sigmoidoscopy, which uses a thin, flexible lighted tube to see the inside of the rectum and part of your colon, usually without sedation, but with bowel-cleaning prep

All home colon cancer tests require you to collect some of your poop, package it up, and send it to a lab or your doctor's office. The details vary. You typically get the kits with a prescription from your doctor, though sometimes you can get them from an online medical provider.

While some nonprescription kits can be found online and in stores, it's better to work with your doctor to choose the best option and discuss the results.

Tests that rely on finding small amounts of blood in your poop are based on the fact that blood vessels on large polyps and cancers are easily damaged by stool passing through your colon. So, they can leave a little blood in your poop.

But it's important to know that polyps and cancers aren't the only possible causes of blood in your stool. Ulcers and hemorrhoids are among other possibilities. If there is blood in your stool, you'll need to follow up with a colonoscopy to see what's going on.

Here are some more details about the two kinds of tests that check for blood, but not abnormal DNA.

Guaiac fecal occult blood test (gFOBT)

This test is recommended less often than FIT, partly because it takes more effort. You'll get a kit with several test cards coated with a chemical substance called guaiac. You'll also get a brush or wooden applicator, a mailing envelope, and detailed instructions.

Before you take this test, you may have to make some changes in your diet and medications.

To do the test, you'll have to collect three bowel movements, by placing a container, plastic wrap, or paper under you when you use the toilet. Each time, you'll need to use the brush or wooden applicator to smear some of the poop on a test card. When dry, the cards go in the mailing envelope, which you need to return within 2 weeks of taking the first sample.

At the lab, a technician will add a chemical to the test samples. They'll change color if blood is present.

Fecal immunochemical test (FIT)

FIT is the more widely used home test for blood in stool. It does not involve any special prep. You'll just need to collect one poop sample according to the directions in your kit.

Typically, you'll be advised to put a piece of paper supplied with the kit across the top of the toilet water and poop onto it. Or you might be instructed simply to poop into a clean toilet. Afterward, you'll use an applicator to collect a bit of the poop from the paper or the toilet bowl and put it in a collection tube or on a test card. You can then flush the toilet, including any collection paper.

You seal the tube or card in a return envelope and put it in the mail. A FIT sample needs to be returned quickly — generally within a day of collecting it. At the lab, technicians will use special equipment to see if your poop has signs of blood in it.

If you choose Cologuard, you'll need a doctor to order the test and have it shipped to your home.

The process for using this test is a little different from other home-based tests because you need to send in a whole poop sample, along with a smaller sample like those used in other tests. The kit for Cologuard comes with everything you need for the test, including a collection tub.

You don't need to do anything to prepare your body for the test. 

To do the test, you put a plastic ring over your toilet bowl that holds the collection tub in place. Then, you poop into the container. After removing the container, you scrape off a small sample of the poop with a probe that goes into a small collection tube. Then, you add a liquid preservative to the larger container and seal that up. 

Finally, you put everything back in the prepaid, pre-addressed box and ship it to a lab.

At the lab, technicians look for not only signs of blood but also DNA changes that might be linked to cancer.

 

While a colonoscopy will find about 99% of colon cancers, Cologuard and other home stool tests will find fewer. But they are repeated more often. Each round of Cologuard testing finds about 9 out of 10 cancers; each round of FIT finds about 8 out of 10; and each round of gFOBT testing finds about 7 out of 10. That's the so-called "sensitivity" of each test — the ability to find a cancer if it's there. 

Keep in mind that these figures are based on two-step testing of positive results — if the home test finds worrisome signs, it's followed by a colonoscopy; if it doesn't, you are done with testing for that round. Repeating the test in 1 or 3 years may find cancers missed earlier. Colon cancers are usually slow-growing.

But there are other measures of effectiveness, including:

False alarms (false positives). This is how often a test suggests you might have cancer when you really don't. Cologuard causes more false alarms than FIT. In one study of nearly 10,000 patients who took both tests, Cologuard was about three times more likely to give a false positive result — meaning no cancer was found on the follow-up colonoscopy.

Lives saved. The bottom line for any cancer screening test is how many lives it saves. Here, there's no firm evidence that any of the recommended screening tests is significantly better than the others. The best available data suggest that for every 1,000 people screened, 24 cancer deaths will be prevented with colonoscopy, vs. 20 for Cologuard and 22 for an annual FIT or the most sensitive annual version of gFOBT.

Your preferences. Doctors like to say that the best screening test is the one you'll use. That differs from person to person. Some people find it easier to show up for a colonoscopy every 10 years than to do a home test annually or every 3 years. Others might never sign up for a screening colonoscopy but will do a home test. So, a home test is more effective for them.

 

 

 

Cologuard, like other screening methods, can give incorrect results. That means it can:

  • Suggest you have colon cancer or precancerous growths when you actually don't, causing worry and leading to a colonoscopy that may not have been needed
  • Suggest there's no problem when there really is one, meaning you miss a chance to catch a growth early

Other downsides include:

  •  A higher cost than other home tests, though generally covered by your insurer
  •  A more involved collection process, as you have to send back a complete bowel movement

During a colonoscopy, your doctor uses a flexible tube and a small camera to look at the lining of your colon and rectum. It is usually done while you are sedated. Colonoscopy remains the gold standard screening tool for colorectal cancer for two main reasons:

  • It finds the most cancers and precancerous polyps.
  • It allows doctors to immediately remove worrisome growths, including precancerous polyps, preventing some colon cancers from ever developing.

Some people also might like the fact that colonoscopy needs to be done only once a decade, vs. every 1 to 3 years for home stool tests.

The downsides of colonoscopy vs. home colon cancer screening tests are:

  • You'll need to take time from your work or other activities to get ready and do the test.
  • You need to clean out your bowels beforehand, which means changing your diet for several days, then going on a liquid diet and using pills or liquids that cause diarrhea.
  • You usually need sedatives or anesthesia, which carry some risk.
  • There's a small risk of bleeding or injuries to your colon.
  • You'll need a ride home from the test because of the effects of sedation.

Keep in mind that using a home test doesn't mean you'll never need a colonoscopy. If the home test finds cause for concern, you will likely need a colonoscopy after all.

Under federal law, Medicare and private insurers are required to cover the costs of colorectal cancer screening tests, including home tests, with no out-of-pocket costs to you. That includes Cologuard, even though it's much more expensive to insurers than other home tests. One study found that Cologuard cost insurers $121 per test, vs. $24 for FIT.

In the past, some private insurers did not cover all the costs of a follow-up colonoscopy if your home test indicated you needed one. Laws have changed and those costs should now be covered. But check with your insurer for details.

There is one catch, if you have Medicare: While you won't pay for the follow-up colonoscopy itself, you might have to pay something for your doctor's services if they remove a polyp or other tissue during the procedure.

Regardless of which home test you use, you should get results in a couple of weeks. Then, you should discuss them with your doctor.

Here's what to know about the results from each of the major home test types:

gFOBT results

Positive. The test found blood. That could come from cancer or polyps, or from something else. So, you need a colonoscopy to know for sure.

Negative. The test found no blood. You should get another test in a year.

FIT results

Positive or abnormal. The test found blood and you'll need a colonoscopy to find the cause.

Negative or normal. The test found no blood and you can do the test again in a year.

Cologuard results

Positive. The test found altered DNA or signs of blood in your poop. You need a colonoscopy to find out the cause.

Negative. The test didn't find altered DNA or blood in your poop. You should get another Cologuard test in 3 years.

With any of these tests, lab errors, poorly prepared samples, or other problems might prevent you from getting a clear result. The testing lab will advise you and your doctor on the next steps if that happens.

Discuss your results with your doctor. If the home test turned up any cause for concern, you'll likely need a colonoscopy. If it didn't, you can continue on your usual screening schedule — every year for FIT or gFOBT and every 3 years for Cologuard.

But keep in mind that those guidelines apply only if you remain at average risk for colon cancer and have no symptoms. Your screening strategy might need to change if you've had a polyp, been diagnosed with an intestinal disease, or learned about a history of colon cancer in your family.

Even if you've been screened, you should talk to your doctor if you have:

  • A change in your pooping habits
  • Blood in or on your poop
  • Diarrhea, constipation, or a feeling you can't empty your bowels
  • Belly pain, aches, or cramps that don't go away
  • Weight loss you can't explain

Home tests for colorectal cancer are a good screening choice for many people, even though they don't find as many cancers as a colonoscopy. There are several home options, so you should talk to your doctor about the best choice for you. If you decide to use home colon cancer testing, it's important to follow the instructions and discuss the next steps with your doctor.

Do doctors recommend at-home colorectal cancer tests?

Yes. Doctors' groups and medical organizations such as the American Cancer Society and the U.S. Preventive Services Task Force include home tests on their lists of recommended screening tests for colorectal cancer. One influential doctors' group, the American College of Gastroenterology, says either colonoscopy every 10 years or FIT testing every year should be the primary screening choices. But the group says Cologuard and tests including flexible sigmoidoscopy can be considered as alternatives. It notes that Cologuard causes more false alarms than FIT. It doesn't include the guaiac fecal occult blood test (gFOBT) on its recommended list, but some other groups do.

Can Cologuard detect polyps? 

Yes, Cologuard detects some polyps, with estimates ranging from 42% to 80%, depending on the size of the growth. Studies suggest colonoscopy detects 72%-83% of polyps.

Print
View privacy policy, copyright and trust info
View privacy policy, copyright and trust info