Introduction The measurement of faecal calprotectin (FC) in patients with suspected bowel inflammation has become routine in many centres in recent years. Although FC levels have been shown to correspond with radio-nucleotide labelled neutrophil scans and endoscopic appearances in those with inflammatory bowel disease (IBD), it is still unclear as to the value of FC to inform IBD diagnosis, especially with regard to endoscopic investigation.

Methods Records of the cohort of all IBD patients diagnosed within our regional paediatric gastroenterology service between 1 January 2005 and 30 June 2010 (aged 1–17 years) and with a FC performed during initial workup were identified. The local laboratory results system and endoscopy lists were reviewed and a non-IBD control who had similarly undergone endoscopy and also had a referral FC level available was identified. Only FC values taken at referral or initial investigation (not repeat samples) in those without any previous gastroenterological diagnosis were included. Patients with insufficient samples (<2 g) and aged <1 year were excluded.

Results A total of 196 patient samples met the inclusion criteria. These included samples from patients with IBD (n=98) (63 Crohn's disease, 24 ulcerative colitis, 11 IBD-U) and 98 controls. The IBD and control group had a male:female ratio of 1.8 and 1.6 respectively (p=0.768). Median values of FC for the IBD group was 1271 μg/g (IQR 691–2000, range 20–2500) and for the control group 48 μg/g (IQR 20–129, range 20–1660). The number of controls with values greater than >200 μg/g was significantly lower in the control group – 16/98 (16%) compared to 91/98 (93%) for IBD (p≤0.0001). Using a cut off of >50 μg/g the sensitivity of FC for IBD diagnosis was 96% [95% CI 90 to 99] and specificity 50% [95% CI 40 to 60]. However, using the locally-accepted clinical range of >200 μg/g the specificity increased dramatically to 84% [95% CI 75 to 90] with sensitivity 93% [95% CI 86 to 97], positive predictive value (PPV) 85% [95% CI 71 to 91] and negative predictive value (NPV) 92% [95% CI 84 to 97].

Conclusion This cohort study demonstrates that FC is a useful tool in determining those who may require endoscopy for suspected bowel inflammation. Those with IBD have significantly higher FC levels at referral and therefore elevated values >200 μg/g should prompt further gastrointestinal investigation.