IBS Fact : Evidence-based management of irritable bowel syndrome

Irritable bowel syndrome vs colorectal cancer

A primary concern of many new IBS patients is their potential risk of developing colorectal cancer. Indeed, studies indicate that patients with a presumptive diagnosis of IBS are 5-7 times more likely to be diagnosed with a colorectal cancer after a detailed examination than those without abdominal complaints. Here, three so-called red flags – unintended weight loss, family history of colon cancer and onset of symptoms after age 50 – have reasonably high predictive value of between 4 and 6%. In contrast, blood in stools has a predictive value of only 2.4 %. Indeed, small amounts of bright red blood usually originate from a haemorrhoid or small tear (fissure) in the anal passage. Rarely, it could be due to another condition that requires treatment, although large amounts of red blood or black, tarry coloured stool does call for urgent medical attention. Although patients with symptoms of IBS seem to have a higher chance of being diagnosed with colorectal cancer than people without abdominal complaint, this association is not causative, i.e. IBS does not predispose for colorectal cancer. Instead, the association is merely caused by overlapping symptoms of IBS and colorectal cancer. Thus, in a fraction of patients with an initial presumptive diagnosis of IBS, and particularly in those with red flags, colorectal cancer may be the underlying cause, which is usually diagnosed following a more detailed endoscopic examination. Fortunately, for the large majority of people with IBS symptoms, including 83.8 % of those with red flags, detailed diagnostic examination reveal no other pathologies, and the diagnosis of IBS can be made with high amount of certainty.

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