Serum Neutrophil Gelatinase B-associated Lipocalin and Matrix Metalloproteinase-9 Complex as a Surrogate Marker for Mucosal Healing in Patients with Crohn's Disease

Background and Aims: Although costly and uncomfortable for the patient, the current standard to assess mucosal healing in Crohn's disease [CD] patients is endoscopy. The aim of this study was to evaluate NGAL-MMP-9 as surrogate marker for mucosal healing in CD patients. Methods: Serum NGAL-MMP-9 levels were determined with sandwich enzyme-linked immunosorbent assay before and up to 5 years after first infliximab infusion in 108 active CD patients [median age at first infliximab 36 years, 57% female] and 43 healthy controls [HC, median age 27 years, 60% female]. Serum samples were matched to the time of endoscopy and complete endoscopic healing was defined as absence of ulcerations. Histological healing was defined as absence of epithelial damage [D'Haens score]. Results: At baseline, median [interquartile range] NGAL-MMP-9 levels were significantly higher in active CD patients vs HC (77.6 [36.9-141.0] vs 25.5 [17.8-42.8] ng/ml; p < 0.001). After treatment, NGAL-MMP-9 levels significantly decreased in completely healed CD patients [n = 38] (84.5 [36.7-138.4] to 23.4 [7.4-42.5] ng/ml; p < 0.001) and-to a lesser extent-in non-healed CD patients [n = 36] (100.9 [43.4-152.6] to 43.8 [27.0-96.8] ng/ml; p = 0.001). Receiver operating characteristic analysis defined a NGAL-MMP-9 cut-off level of 45ng/ml corresponding to complete endoscopic healing (area under the curve [AUC] = 0.79, 82% sensitivity, 65% specificity) and histological healing [AUC = 0.72, 79% sensitivity, 53% specificity]. At baseline, C-reactive protein [CRP] was not elevated in 33% of active CD patients, whereas 53% of these patients did have elevated NGAL-MMP-9 levels. Conclusions: In the search for surrogate markers to assess mucosal healing in inflammatory bowel disease, NGAL-MMP-9 supplements and outperforms CRP in both ulcerative colitis and CD patients.