At the moment, we’re pretty ‘sensitive’ at spotting IBD (i.e. we pick up nearly all cases), but we also refer a lot of patients who don’t have IBD (i.e. we’re not very ‘specific’). This is expensive and means that some patients end up with colonoscopies that they don’t need.
Faecal calprotectin is secreted into the gut during an inflammatory process. There is normally a certain cut-off in its interpretation. Below that cut-off is considered to be ‘negative’ and above is ‘positive’. A ‘negative’ result suggests IBS. The idea is that we only need to do this test if we are considering specialist referral. If it comes back ‘negative’, then you would think twice about referring.
Just to give you the stats, if someone presents to us with lower GI symptoms, the chance of them having IBD is about 6.3%. Faecal calprotectin has a negative predictive value of about 98% (so 98% of those with a negative test will not haveIBD – but 2% will have IBD). So not perfect, but pretty good.