What is the sensitivity of the FIT test?
Conclusion FIT sensitivity is maximised to 97.0% at the lowest cut-off (2 µg/g); a negative FIT result at this cut-off can effectively rule out CRC and a positive FIT result is better than symptoms to select patients for urgent investigations.
Cologuard is better at detecting cancer than FIT (92% vs 74% for FIT), but the false positive rate is higher. Cologuard has a 13% false-positive rate, and that rate increases as people age. Cologuard is less accurate than a colonoscopy at detecting polyps of any size.
Fecal immunochemical test (FIT)
Studies show that FITs can be nearly 80% accurate in detecting colorectal cancer. The test should be done annually.
FIT results of more than 10 are deemed positive – patient has a 1 in 4 chance of Lower GI cancer. When FIT is less than 10 it suggests a low probability of Lower GI cancer, although these do occur. Patients with bowel cancer and a FIT less than 10 often have other symptoms.
FIT has a false positive rate of about 5%, which again, needs to be followed up with a colonoscopy. The tier 2 test, the FIT-Fecal DNA Test, is designed to detect microscopic blood as well as abnormal DNA in stool samples.
Cancer outcomes
The positive predictive value of FIT in this low-risk symptomatic population is 7.0% (95% CI 5.1–9.3%), and the negative predictive value is 99.8% (CI 99.5–99.9%).
However, in terms of polyp detection, the comparison is vastly different. Here, the FIT-fecal DNA test proved a detection rate for high-grade dysplasia of 62%, which then fell to 42% for detecting any type of polyp. Comparatively, colonoscopy is 75%–93% sensitive for finding any type of polyp smaller than 6 mm.
False-positive (FP) results of fecal immunochemical tests (FITs) conducted in colorectal cancer (CRC) screening could lead to performing unnecessary colonoscopies. Hemorrhoids are a possible cause of FP FIT results; however, studies on this topic are extremely rare.
FIT detects signs of colon and rectal cancer. It can also detect some polyps, which are growths that could become cancer later. HOW? You will get a kit from your provider or in the mail with instructions about how to take a sample of stool.
However, in terms of polyp detection, the comparison is vastly different. Here, the FIT-fecal DNA test proved a detection rate for high-grade dysplasia of 62%, which then fell to 42% for detecting any type of polyp. Comparatively, colonoscopy is 75%–93% sensitive for finding any type of polyp smaller than 6 mm.
What can cause a false positive FIT test?
A false positive test would occur when the test was positive but you do not have any signs of polyps or cancer. This happens approximately 25% of the time. This can be the result of other issues (such as inflammation or hemorrhoids) causing blood to be present in the stool.
A FIT test is similar to an FOBT, except the FIT test is newer and doesn't require a restricted diet before. A FIT test may not detect blood from further up the digestive tract (such as the stomach), which means it is more specific to finding blood coming from the lower gastrointestinal tract than the FOBT.
