OBJECTIVES: The inflammatory bowel diseases (IBD) are characterized by chronic inflammation of the gastrointestinal tract; the irritable bowel syndrome (IBS) is a functional disorder (prevalence 10%-20%). They present overlapping symptoms, making diagnosis difficult in primary care. Endoscopy is the gold standard for IBD, but it often turns negative due to IBD’s low prevalence, it is expensive, uncomfortable and risky for the patient. F-Calprotectin is a marker of intestine inflammation: as IBD patients exhibit levels higher than the general population and IBS patients, F-Calprotectin can be used to rule out IBD. The only CE evaluation on F-Calprotectin has been published by NHS (CEP09041, 2010); based on new evidence, we propose a refined model to evaluate the CE of F-Calprotectin compared to the standard pre-endoscopic serologic test (CRP+ESR) to distinguish IBD from IBS in the UK and Brazil. METHODS: F-Calprotectin sensitivity (0.96) and specificity (0.96) were evaluated from a meta-analysis performed in March 2013; CRP+ESR sensitivity (0.35) and specificity (0.73), and the costs come from CEP09041. Published HRQoL values for IBD and IBS were transformed in QALYs with transfer-to-utility techniques. The outcomes included cost savings, cost per QALY. Uncertainty was addressed with a probabilistic sensitivity analysis. RESULTS: Results for UK show that F-Calprotectin is CE with respect to CRP+ESR: a) it results in more corrected IBD diagnoses at a lower price (it costs 113£ less per patient); b) it reduces the number of unnecessary endoscopies, increasing the number of correctly diagnosed IBD (N=59) and IBS (N=195) patients; c) it brings about a QALY gain per patient equal to 0.0034QALYs; the ICER of the CRP+ESR diagnostic strategy is 47,783£, and it falls well outside the cost-effectiveness bounds (20,000–30,000£ per additional QALY). Similar results were found for Brazil. CONCLUSIONS: F-Calprotectin is CE to rule out IBD in primary care in UK and Brazil.