Relationship between serum infliximab trough levels and endoscopic activities in patients with Crohn's disease under scheduled maintenance treatment

Few data are available to support the clinical relevance of infliximab (IFX) trough levels for prediction of endoscopic disease activity in Crohn's disease (CD). This study evaluated the endoscopic disease activities in relation to clinical outcome using several laboratory markers including serum IFX trough levels in patients with CD undergoing scheduled IFX maintenance treatment. A total of 78 sessions of endoscopy were performed on 45 patients with CD. Endoscopic activity was assessed using the modified Rutgeerts scoring system. IFX trough levels and anti-IFX antibodies (ATIs) were determined by immunoassays. Endoscopic activity negatively correlated with serum IFX trough levels (Spearman's rank correlation coefficient (rho) = -0.54, P < 0.0001) and serum albumin levels (rho = -0.46, P < 0.0001), and positively correlated with CRP (C-reactive protein) levels (rho = 0.55, P < 0.0001), ESR (erythrocyte sedimentation rate) (rho = 0.47, P < 0.0001) and fecal calprotectin levels. IFX trough levels and serum albumin levels were significantly elevated in the mucosal healing (MH) group, but ATIs, CRP, ESR and fecal calprotectin levels were significantly elevated in the nonmucosal healing group. Receiver operation curve revealed that the optimal cutoff value of IFX trough levels for identifying normal laboratory markers was 0.6 mu g/ml for CRP, 1.0 mu g/ml for serum albumin and 1.1 mu g/ml for fecal calprotectin. Identification of mucosal healing needed a higher cutoff value of 4.0 mu g/ml. Thiopurine treatment did not affect IFX trough and ATI levels. Mucosal healing requires higher IFX trough levels, compared to those to achieve normalization of routine clinical markers.