What test for fecal occult blood is superior to guaiac testing but is not commonly used clinically?
In FIT, antibodies to human hemoglobin are collected from venipuncture of rabbits previously exposed to human blood and are coupled to fluorescent proteins for easy detection. These antibodies attach to human blood (hemoglobin) in stool and are detected by their fluorescence. The FIT test is superior to guaiac tests for detection of colon cancer and colon adenomatous polyps. In Japan, patients with a positive FIT screening test undergo colonoscopy as the diagnostic test.
Advantages of FIT Test
• Specific for human hemoglobin, does not recognize cow or other mammalian hemoglobin.
• There are no false positive results with cabbage, cauliflower, or broccoli (pseudoperoxidase).
• Hemoglobin released from UGI tract bleeding is digested, and is not immune reactive to FIT.