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P223. Faecal calprotectin testing in primary and secondary care - Are the current manufacturer's cut-off values clinically useful?

S. Lee1, H. Borthwick2, A. Dhar1, 1County Durham & Darlington NHS Foundation Trust, Gastroenterology, Co. Durham, United Kingdom, 2County Durham & Darlington NHS Foundation Trust, Clinical Biochemistry, Co. Durham, United Kingdom

Background

Faecal Calprotectin (FC) is a protein complex found in high concentrations in neutrophils and is released within the bowel when inflammation occurs. It can be measured quantitatively using ELISA and is very sensitive and specific in discriminating inflammatory from non-inflammatory pathologies causing diarrhoea. The manufacturer recommends a positive stool FC test (>60 µg/g) to be indicative of inflammation and further investigations (e.g. endoscopy, histology and imaging) and referral to a Gastroenterology clinic is advised.

Aims: To determine whether the manufacturer's cut-off levels for referral (>60 µg/g) are clinically useful in making a positive diagnosis in patients presenting with chronic diarrhoea.

Methods

We analysed the outcome of 122 FC test results done in primary and secondary care during a 3 month period from October to December 2011 performed on patients who presented with chronic diarrhoea without a pre-existing diagnosis of Inflammatory Bowel Disease (IBD).

According to manufacturer's guidance, a FC result of >60 µg/g was considered positive and <60 µg/g negative. Positive FC patients were seen in a Gastroenterology Clinic and investigated appropriately. The primary outcome of this study was to record the final diagnosis arising out of FC testing and investigations thereof. Secondary outcomes were to correlate FC levels to the final diagnosis.

Results

Of 122 FC tests, 41% (n = 51) were read as positive vs. 58% (n = 71) negative. 19/51 (37%) FC positive patients had a positive organic diagnosis (IBD = 9, Diverticulosis = 5, Colonic Polyps = 3, Infective colitis = 1 and Chronic Pancreatitis = 1) while the remaining 32 pts (63%) were given a diagnosis of functional bowel disorder after investigations.

Of 71 patients testing negative on FC, 94% (n = 67) had functional bowel disorder; only 6% (n = 4) were found to have an organic condition, none of them IBD. This correlates with a positive predictive value of 37% and a negative predictive value of 94% for organic disease. The FC levels of those tested positive with a diagnosis of functional bowel disorder ranged from 61 to 547 µg/g (mean 153 µg/g) whereas FC values of those with organic conditions ranged from 63 to 1573 µg/g (mean 746 µg/g).

Conclusion

The current manufacturer's cut-off at >60 µg/g is not clinically useful to diagnose an organic bowel pathology and further studies are needed to determine the true cut off value for a higher yield of a positive diagnosis. Cost effectiveness studies are also needed to determine referral cut off values.