A FIT test (fecal immunochemical test) is a simple at-home screening tool that checks your stool for tiny amounts of blood you can’t see with the naked eye. Hidden blood in stool can be an early sign of colorectal cancer or precancerous growths called polyps. The test uses antibodies that react specifically to human blood, so unlike older stool tests, it won’t be triggered by a rare steak or iron supplements. It’s one of the most common first-line screening options for colorectal cancer, recommended annually for adults aged 45 to 75.
How the FIT Test Works
Colorectal cancers and larger polyps tend to bleed intermittently as stool passes over them. The amounts are usually far too small to notice in the toilet, but the FIT test can pick them up. It targets the globin protein in human hemoglobin, which means it’s highly specific to blood from your own digestive tract. Blood from food you’ve eaten gets broken down before it reaches the lower intestines, so it doesn’t interfere with results.
This specificity is a major advantage. Older guaiac-based stool tests (sometimes called FOBT) detected a different component of blood and could react to red meat, certain vegetables, and vitamin C supplements. Those tests also required three separate stool samples and dietary restrictions for days beforehand. FIT needs just one or two samples and requires zero preparation: no dietary changes, no medication adjustments, nothing.
What the Collection Process Looks Like
Your doctor’s office or screening program will mail or hand you a small kit. The specifics vary by brand, but a typical kit from a major cancer center includes a test card, a small brush, a specimen bag, and a prepaid return envelope. The whole process takes a few minutes in your bathroom.
You flush the toilet two or three times before your bowel movement to clear any residue, then go as usual. Without flushing, you gently brush the surface of the stool for about five seconds to pick up a thin smear. If the stool is loose, you stir the water around it with the brush instead. You apply the sample to the test card, close it, seal it in the specimen bag, write the date, and drop it in the mail. Results typically come back within a few days to two weeks depending on the lab.
How Accurate FIT Is
FIT is good at catching colorectal cancer when it’s present, and its accuracy improves with more advanced disease. A large meta-analysis published in the American Journal of Gastroenterology found that FIT detects about 73% of stage I colorectal cancers and around 80 to 82% of stage II and III cancers. Its specificity, the ability to correctly give a negative result when cancer isn’t there, sits around 87 to 95% depending on the population tested.
Where FIT falls short is with precancerous polyps. It catches only about 16 to 34% of advanced adenomas, the type of polyp most likely to eventually become cancer. This is why annual testing matters so much. A polyp that doesn’t bleed enough to trigger the test one year may bleed the next, and yearly screening significantly increases the chance of catching a problem before it progresses.
By comparison, colonoscopy has higher sensitivity for both cancer and polyps because the doctor visually inspects the entire colon. But colonoscopy requires bowel prep, sedation, a day off work, and carries a small risk of complications. Many people who decline or delay colonoscopy will complete a FIT test, making it a practical alternative that still saves lives when done consistently.
What a Positive Result Means
A positive FIT result means blood was detected in your stool. It does not mean you have cancer. The test cannot diagnose cancer on its own. The standard next step is a diagnostic colonoscopy to find the source of bleeding. During that procedure, if the doctor finds polyps, they can remove them on the spot, which actually prevents future cancers from developing.
Many positive FIT results turn out to be caused by something other than cancer. Hemorrhoids, diverticular disease, and minor inflammation in the colon can all produce small amounts of bleeding. In screening studies, more than half of people with a positive FIT had no advanced growths found on follow-up colonoscopy. Still, completing that colonoscopy is important. Research from the National Cancer Institute has shown that getting a colonoscopy after a positive FIT significantly reduces the risk of dying from colorectal cancer, largely because it catches treatable problems early.
What Can Affect Your Results
Certain factors raise the chance of a false positive, meaning the test flags blood that isn’t coming from cancer or polyps. Hemorrhoids and diverticular disease are common culprits because both can cause low-level bleeding in the lower digestive tract. Smoking, heavier alcohol use, and higher body weight are also associated with more false positives.
False negatives, where cancer or a significant polyp is present but the test comes back normal, happen too. About 31% of people with advanced growths had a negative FIT in one large study. This is partly because not all cancers and polyps bleed continuously. Younger adults, nonsmokers, and people at a healthy weight were slightly more likely to get false-negative results, possibly because their growths tended to be smaller or less prone to surface bleeding. Again, this is why repeating the test every year matters. A single negative result is reassuring but not a guarantee.
Who Should Get Screened and How Often
The U.S. Preventive Services Task Force recommends colorectal cancer screening for all adults aged 45 to 75. This age range was expanded from the previous starting point of 50, reflecting rising rates of colorectal cancer in younger adults. If you choose FIT as your screening method, it should be done every year. An alternative option, a combined stool DNA-FIT test (sold under the brand name Cologuard), is recommended every one to three years but is a different, more expensive test.
People with a family history of colorectal cancer, a personal history of inflammatory bowel disease, or certain genetic conditions may need to start screening earlier or use colonoscopy as their primary method. Your screening schedule in those cases would be based on your individual risk.
Cost and Insurance Coverage
Under the Affordable Care Act, both private insurers and Medicare are required to cover colorectal cancer screening tests recommended by the USPSTF with no out-of-pocket cost to you. That means no copay and no deductible for a FIT test if you’re in the recommended age range. Medicare specifically covers FIT once every 12 months for people 45 and older, at no cost as long as the provider accepts Medicare’s standard payment. Without insurance, FIT kits are relatively inexpensive compared to other screening options, generally costing far less than a colonoscopy, though exact prices vary by lab and provider.