Stool tests for colorectal cancer

A stool test is a fairly simple, non-invasive colon cancer screening option. There are several types of fecal or stool-based tests available, and each has its share of advantages and disadvantages to consider. Unlike a colonoscopy, these tests don’t require prep work.  

It’s important to note, however, that if you have a positive result, you will still need a colonoscopy or another test to confirm the findings and remove any precancerous polyps. Colonoscopy, a visual and more detailed exam of the colon, is considered the best option for colorectal cancer screening.

Fecal immunochemical test (FIT)

Also known as: Immunochemical fecal occult blood test, iFOBT

Why it’s performed: The fecal immunochemical test (FIT) looks for hidden blood in the stool. This may be an early sign of colon cancer, although not all cancers or polyps bleed. This test only detects blood that comes from your lower intestines, not further up your digestive tract.  

What happens during the procedure: Your doctor will give you a kit that contains detailed instructions on how to collect a stool specimen. Basic instructions include:  

• Unfold the collection paper and place it inside the toilet bowl, so it floats on top of the water. 
• Use the bathroom on top of this paper.  
• To gather a sample, open the FIT tube and scrape the grooves at the end of the stick along your stool until the grooves are fully covered.  
• Place the stick with the sample back into the FIT tube. 
• Mail or drop off your test within two days. (Make sure to write the date on the tube, as directed.) 

What the results mean: If your FIT results show that you have blood in your stool, your doctor may order other tests. A normal result means the test did not detect any blood in the stool, and more testing typically isn’t required. It takes roughly one to three days to get results.

Cost: Medicare covers FIT once a year if you’re 50 or older, as do most private insurers. 

Pros and cons: It’s easy to do, it takes just a few minutes and no changes to your diet or current medication regimen are needed. Just one stool sample is needed, unlike other stool tests that may require multiple samples.

Fecal occult blood test (FOBT)

Also known as: Guaiac test, gFOBT, guaiac smear test 

Why it’s performed: The fecal occult blood test (FOBT) looks for hidden or occult blood in the stool. Guaiac is used to coat the FOBT test cards. It creates a chemical reaction with stool if blood is present. This test can’t determine if the blood is from your colon, rectum or other parts of your digestive tract. For this reason, it’s considered less specific than the FIT test.

What happens during the procedure: This test can be performed at home or during a regular appointment as part of a rectal exam. At home, you’ll be asked to: 

• Collect a stool sample from three different bowel movements.  
• Smear a small amount of stool on a card provided in the kit for each bowel movement.  
• To get the stool sample, place a sheet of plastic wrap or paper across the toilet bowl to catch the stool, or use a dry container to collect it. (Don’t take stool samples directly from the toilet bowl water.)  
• The cards are sent to a laboratory for testing.  

Unlike FIT, the FOBT test does require some prep. 

The foods that may affect test results and should be avoided include: 

• Red meat 
• Cantaloupe 
• Uncooked broccoli 
• Turnip 
• Radish 
• Horseradish 

Also, certain medicines can interfere with the results, namely vitamin C, aspirin and non-steroidal anti-inflammatory drugs such as ibuprofen and naproxen. Tell your doctor about any and all medications that you’re taking to find out if they’ll affect the accuracy of your results. 

What the results mean: If there is blood in your stool, it may be coming from the stomach or intestinal tract. There are many potential reasons for this, including colon cancer or colon polyps, but it also may be false-positive. It typically takes roughly one to three days to get results. You’ll likely need a colonoscopy if the FOBT test is positive.  

Cost: Medicare covers yearly FOBT if you’re 50 and older, as do most private insurers. Call your carrier to make sure the cost is covered. 

Pros and cons: This stool-based test is inexpensive and can be done at home. If it’s done during a rectal exam, however, it may be uncomfortable. It has a high false-positive rate, because it is not specific for human blood and casts a wider net than FIT. You also have to watch your diet before the test and may need to stop taking certain medications for more accurate results.

Stool DNA testing

Also known as: Cologuard^®

Why it’s done: Stool DNA testing is a newer type of non-invasive stool-based test to check for colorectal cancer. It looks for certain DNA or genetic changes that may suggest pre-cancerous growths or cancer cells. It should be repeated every three years. 

What happens: Your doctor will order a kit that contains everything needed to collect a DNA stool sample. To start: 

• Unfold the bracket and place it under your toilet, according to instructions.  
• Place the sample container into the top of the bracket.  
• After you have had a bowel movement, scrape the stool sample with the probe to get another small sample for the Cologuard test.  
• The stool sample must have a preservative poured onto it to make sure it can be tested. 

You don’t have to make any changes to your diet or medication regimen to take this test. 

What the results mean: If a stool DNA test finds something abnormal, a colonoscopy may be needed to follow up on the findings. Your doctor should have the results within two weeks from the time that the sample is received at the lab. 

Cost: Stool DNA tests are more expensive than other stool-based tests. If it’s not covered by insurance, the cost is around $565. 

Pros and cons: There is no prep required, and this test requires only one stool sample. It is believed to be more accurate than the FIT test.

Shared decision-making

Everyone is different, so it’s important to discuss personal medical history and risk factors with your doctor when deciding which colorectal screening methods are most appropriate for you and how often you should be screened.