Els van de Vijver

73 applying the decision strategy in a clinical setting in terms of patient outcome, health professionals’ behaviour, and resource use. In this study we used the enzyme-linked immunosorbent assay of one manufacturer. Although other test kits have an acceptable agreement in the lower range (below 250 µg/g),(18) inter-assay variability is considerable above this cut-off point. We emphasize the need for assay standardisation, but in its absence assay-specific cut-offs may improve diagnostic performance. In the strategy with blood markers, we relied on a subgroup of commonly used laboratory data, that is CRP and Hb. We did not include erythrocyte sedimentation rate (ESR), as an inverse correlation exists between Hb and ESR that could hamper the interpretation of our statistical model. Neither did we include albumin, which is known to be abnormal in a considerable proportion of paediatric patients with severe IBD,(19,20) but was a highly unusual clinical presentation in our study cohort. Implications for practice In many decision curves there is a trade-off in net benefit when risk thresholds increase. This is hardly the case with the optimal decision strategy in this study, where the graph takes an almost horizontal course. Paediatricians can be reassured that properly evaluating children using clinical findings, CRP, haemoglobin and calprotectin is a highly accurate non-invasive approach to investigation of possible IBD in any clinical setting. CONCLUSION Evaluating symptoms plus blood and stool markers in patients with non-bloody diarrhoea is the optimal test strategy that allows paediatricians to reserve a diagnostic endoscopy for children at high-risk for IBD. ACKNOWLEDGEMENTS The following investigators were, together with the authors, members of the CACATU consortium: J. Homan-van der Veen (Deventer Hospital), O. Norbruis (Isala Clinic), S. van Dorth (Tjongerschans), T. de Vries (Medical Center Leeuwarden), B. Delsing (Treant Zorggroep Hoogeveen), L. van Overbeek (Treant Zorggroep Emmen), A. Kamps (Martini Hospital Test strategies to predict IBD 73