This test is used to help detect adenomas (tumours) and colorectal cancer, as well as to identify individuals who should undergo a colonoscopy.
Large polyps, adenomas, and colon cancers release small amounts of blood into the intestine, but these amounts are too small to be seen with the naked eye. Screening for traces of blood in the stool using the immunological technique detects these very small traces of blood, with no interference from medications or food intake. A single specimen can be used to detect approximately 65% of significant lesions of the colon. Repeat tests on a regular basis, ideally every year, increase this detection rate.
A positive result indicates an approximately 25% probability that the colonoscopy reveals a significant lesion (large polyp or adenoma), which can be removed during the examination. The probability of colorectal cancer is approximately 2.5% (1 chance in 40). A negative result does not necessarily mean the absence of all lesions, but in individuals at average risk, it means the colonoscopy can be performed at a later date.