Unlike colonoscopies (which visually look for irregular growths with a camera), the FIT examines stool samples for human hemoglobin, a protein in red blood cells. If human hemoglobin is present, blood has likely leaked into the digestive system, according to Dr. Theodore R. Levin, a gastroenterologist with Kaiser Permanente in Northern California.
Why does this matter? Well, cancerous tissue — and even large benign polyps — is more likely to bleed than normal health tissue in the colon, Levin said. But the blood isn’t always noticeable when you go to the bathroom. In fact, the FIT was designed because growing polyps and cancers tend to microscopically bleed, according to Dr. Luigi Ricciardiello, a professor of medicine in the department of gastroenterology, hepatology and nutrition at The University of Texas MD Anderson Cancer Center in Houston.
A positive result indicates there’s blood in your stool, which could mean you have colorectal cancer. That said, abnormal test results do not automatically mean you have cancer, as there are other health conditions, like hemorrhoids or benign polyps, that also cause bleeding. If your FIT finds blood, however, you’ll definitely want to follow up with a colonoscopy to get an accurate diagnosis, Levin advised. “A positive FIT test should never be the end test. A next step is needed,” Ricciardiello said.
