Mapping of Crohn's disease outcomes to faecal calprotectin levels in patients maintained on biologic therapy

Background Faecal calprotectin (FC) is a sensitive marker of intestinal mucosal inflammation. The gold standard in Crohn's disease management is mucosal healing. The role of FC to support clinical practice in Crohn's disease is not yet defined. Aims To determine, in patients with Crohn's disease established on biologic therapy: (1) the correlation between disease activity and FC levels, (2) whether FC can predict for relapse and (3) the sensitivity and specificity of the C-reactive protein (CRP) when compared with FC. Methods In this retrospective, single-site study, Crohn's disease activity, clinical outcomes, FC and CRP of 76 patients established on biologic therapy were reviewed and mapped over time. Results Patients were mapped for a median of 34 months (IQR 21-57.5). FC levels were determined every 7 (4-13) months on average. Mean FC in quiescent disease was 105 mu g/g (SEM 19); in mild disease, 282 (SEM 71); in moderate disease, 611 (SEM 80) and in severe disease, 1314 (SEM 224) (p<0.001). In asymptomatic patients who relapsed at 6 months, the optimal FC, with an area under the curve of 0.886 (p<0.001), was 357.5. In discriminating quiescent from active disease (FC>100 mu g/g) the sensitivity and specificity of CRP were 0.48 (0.36-0.61) and 0.73 (0.6-0.85), and in mild from moderate or active disease (FC>250 mu g/g ), 0.60 (0.43-0.74) and (0.72 (0.60-0.82). Conclusions FC is an accurate marker of Crohn's disease activity and predicts for relapse, thus providing the clinician time to optimise therapy. FC is a more sensitive marker of Crohn's disease activity than CRP.