We previously showed a discrepancy between a commercially available enzyme-linked immunosorbent assay (ELISA) and the homogenous mobility shift assay (HMSA) for both infliximab and adalimumab concentrations in patients with inflammatory bowel disease (IBD).1 Based also on the results of this study, Prometheus Laboratories initiated a comprehensive review of their HMSA assays and found that there was an upward drift for both infliximab and adalimumab over a 2-year period, including when our study was being performed.