Therapeutic Drug Monitoring of Anti-TNFα Inhibitors: A Matter of Cut-Off Ranges

Therapeutic drug monitoring (TDM) is a useful tool for optimising the use of anti-TNFα inhibitors in patients with inflammatory bowel diseases (IBDs). Recently, point-of-care methods for the quantification of drug levels and anti-drug antibodies (ADAs) have been developed to overcome the limitations of conventional enzyme-linked immunoabsorbent assays (ELISAs). Here, we evaluated the performance, interchangeability, and agreement between an automated ELISA-based immunoassay (CHORUS Promonitor) and the lateral flow assay (RIDA®QUICK) for the quantification of infliximab (IFX, n = 65) and adalimumab (ADM, n = 58) plasma levels in IBD patients. Thirty-two samples for IFX and twenty-three samples for ADM that tested positively for the presence of ADAs were also used. Overall, data analysis showed a good agreement of ADM trough concentrations (R2 = 0.75) between the two assays as well as for ADA measurement (K > 0.8). However, IFX levels highlighted a weak correlation (R2 = 0.58) between the two kits, with the RIDA®QUICK assay overestimating IFX plasma values by 30% when compared to the CHORUS Promonitor kit. Results from this study show that the two assays are not quantitatively and qualitatively interchangeable due to substantial discrepancies in some results. Accordingly, the same assay should be used for the longitudinal follow-up of IBD patients.