Els van de Vijver

15 Evaluating the accuracy of the calprotectin stool test In 2010, we wrote a diagnostic meta-analysis (11) on the applicability of calprotectin as a triage test. All the articles included in that meta-analysis were based on the fully paired design that is typical of Phase II diagnostic accuracy studies. In these studies, a group of patients suspected of having IBD underwent faecal calprotectin testing followed by the reference standard: endoscopy. These studies estimated the diagnostic accuracy of faecal calprotectin under ideal experimental conditions. In the next phase, a triage test (e.g. faecal calprotectin) needs to be used as means of triage before performing the existing diagnostic test (i.e. endoscopy), and only patients with positive results on the triage test will continue along the diagnostic pathway (see Figure 1 ). In ‘Phase III’ diagnostic accuracy studies, accordingly, not all suspected patients would need to undergo the reference standard.(12) To date, no Phase III diagnostic accuracy studies have been performed with regard to the potential value of faecal calprotectin. Therefore, we set ourselves to test the accuracy of faecal calprotectin with respect to the identification of patients with gastrointestinal complaints that should be referred for endoscopy because of IBD. In Chapter 2 we assess the role of faecal calprotectin as a triage test in the diagnostic work- up of children with gastrointestinal complaints (such as chronic abdominal pain, diarrhoea) in a Phase III diagnostic accuracy study. All children will have a faecal calprotectin test, but not all suspected patients will undergo endoscopy. The decision to expose a patient to endoscopy will be based on the physicians’ clinical gut feeling. They are blinded to the FC result and consequently cannot take this result into account. Faecal calprotectin is not the only marker for intestinal inflammation. Another candidate marker that could aid in differentiating IBD from IBS is Calgranulin-C (S100A12). Calgranulin- C is released almost exclusively by activated granulocytes, and has hardly been investigated as a marker of intestinal inflammation.(13) In previous case control studies, calgranulin-C showed diagnostic promise, exhibiting better specificity for intestinal inflammation relative to calprotectin.(14-16) In Chapter 3 , we investigate the use of calgranulin-C to predict IBD in children and teenagers with chronic abdominal pain and diarrhoea, and we compare its accuracy to that of the calprotectin stool test. General introduction