icroscopic presence of blood. This type of screening helps doctors diagnose benign (noncancerous) conditions and detect the presence of colorectal cancer.
The US Food and Drug Administration (FDA) has approved a few different stool tests that can be used for colon cancer screening. The collection methods referenced above are typical but may vary according to test kit manufacturers. For best results, following the directions and ensuring kits are used before the expiration date is important.
Fecal Immunochemical Test (FIT or iFOBT)
A more affordable and highly sensitive test, the FIT, involves the use of antibodies that bind to hemoglobin protein — a protein that indicates whether blood is present in the stool. Collecting a stool sample is fairly simple: a fecal sample is scraped with a small probe, inserted into a sampling container, and returned to the lab. Although a change in diet isn’t required before testing for the FIT, certain medications may affect test results. It is best to consult with your healthcare provider about what to avoid or modify before the test.
Guaiac FOBT (gFOBT)
The gFOBT also looks for blood in the stool — specifically, the presence of heme, a component of hemoglobin. Samples from a few different bowel movements are taken with applicator sticks, smeared onto a paper card coated with guaiac, and then sent back off for testing. At the lab, hydrogen peroxide will be added to the card. Cards that turn blue mean that blood is present.
The gFOBT is very sensitive. Therefore, before testing, your doctor may ask you to stop eating foods containing heme in preparation to avoid a false positive. This might include refraining from red meat, poultry, seafood, turnips, horseradish, and citrus fruits and juices. Certain nonsteroidal anti-inflammatory drugs (NSAIDs) and supplements, such as Vitamin C and iron, can also affect test results. Be sure to ask your doctor if there are any adjustments you need to make before you take the test.
Stool DNA Test (FIT-DNA)
This is a test that combines the FIT with additional screening for DNA cells that are shed from the colon and the rectum during a bowel movement. Cologuard is a commonly used brand for this test. Upon receipt, the lab extracts DNA from the stool to identify whether or not mutated or abnormal genes are present. This test collects a full stool sample and does not require dietary changes.
Whatever test is used, it should not be used by women who are menstruating—testing while on your period can produce a false positive.
What the Results Mean for You
Blood in the stool does not necessarily mean you have cancer. There are many other conditions, such as IBD, ulcers, hemorrhoids, colon polyps, or anal fissures, that could be contributing to gastrointestinal bleeding. If blood is found, your doctor will likely recommend additional testing to determine the cause of your positive test result.
Additionally, tests such as Cologuard will look for genetic changes that could signal the presence of colorectal cancer. The results will indicate if any mutations are present.
If you receive a negative test, no blood was found in the sample, and no genetic changes were noted.
Should you receive inconclusive — neither positive nor negative — results, it’s possible that there was an issue with your specimen. In cases such as this, your primary care physician might recommend testing again.
Your doctor will be able to discuss the risks of receiving either a false-positive or false-negative result. Despite the risk, the National Cancer Institute points to probable benefits, “Studies show that some screening tests for colorectal cancer help find cancer at an early stage and may decrease the number of deaths from the disease.”
Visual Tests Used for Colorectal Cancer Screening
While there are advantages to at-home colon cancer tests, they also have some disadvantages. Even though convenient and non-invasive, at-home tests aren’t as accurate as other types of colon cancer screening. Their higher probability of false positives and false negatives means that you’re likely to need foll