Why FOB testing of symptomatic patients is daft

colorectal cancer shrewsbury shropshire surgeon Cheetham

NICE published new guidance for the referral of patients with suspected cancer to secondary care in 2015. The explicit aim was to lower the threshold for referral to secondary. I’m sure the authors had honourable motives, yet some of the resulting guidance may have unintended consequences. I’m particularly troubled by the suggestion that a group of patients with lower risk of colorectal cancer should be investigated with faecal occult blood testing (FOB) , rather than a more definitive radiological or endoscopic test. Indeed there seems to be a conflict between NG12 (NICE guidance for investigation of patients with suspected cancer)  and the published NICE guidance for the diagnosis and management of colorectal cancer.

So what’s the problem?

Well in short there are no high quality research studies looking at how FOB performs in people with symptoms. It seems that the NICE team have extrapolated from studies where FOBt have been used to screen whole populations. In screening studies, it is reckoned that with careful quality control, FOBt will pick up about 50% of bowel cancers. Now that may be ok if we are testing a group of people without symptoms and trying to pick up some cancers before they cause symptoms. If we have a group of patients with symptoms, they want to now what’s causing them or they want to have serious illness (such as bowel cancer ruled out). The problem with using a test with such a low sensitivity in this situation is that it cannot effectively rule out bowel cancer, in fact it’s about as accurate as tossing a coin. I suspect that most patients and their GPS would want to use a more sensitive test in this circumstance. So FOBt may only pick up about 50% of cancers, but more importantly it may falsely reassure people with a negative test (the negative predictive value of the test is also poor). This means that their could be a group of people with symptoms who have rightly gone to see their GP and been falsely reassured that they doe not have cancer. This may result is them not seeking further medical attention and perversely could result in a worse outcome for this group. While NICE were writing these guidelines an eminent group of researchers and clinicians wrote and asked for the guidance to be changed. Sadly NICE did not do this – you can read here  a letter the same group wrote on this subject.

So what’s the future?

Many CCGs including all of those in London have decided not to commission FOB for symptomatic patients because of these concerns. A newer test called FIT is being introduced into the bowel cancer screening programme . FIT is also being evaluated in trials of symptomatic patients  and this looks more promising. For the moment, GPs should continue to use their judgement and refer patients with suspicious bowel symptoms for a colonoscopy or a consultation with a colorectal surgeon.