Comparison of infliximab drug measurement across three commercially available ELISA kits

The monitoring of infliximab drug levels aids in the management of several autoimmune diseases, notably inflammatory bowel disease. Several commercial kits are now available and approved by the Therapeutic Goods Administration (TGA) for the measurement of infliximab levels, but there have been limited verification or comparison studies to date. Finding an assay that most accurately measures infliximab is essential for optimal drug titration and patient management. We performed this study to compare the performance of the Grifols Promonitor, Theradiag Lisatracker and R-Biopharm Ridascreen enzyme linked immunosorbent assay (ELISA) kits. Preparations of serum containing known concentrations of infliximab were assayed using each kit, including in the presence of interference from anti-infliximab antibodies, autoantibodies and other biological agents. The Lisatracker kit provided the most accurate determination of infliximab drug levels, however it yielded false positive results at low concentrations of infliximab. The average coefficients of variation (CVs) for the kits were 8% for Lisatracker, 5% for Ridascreen and 11% for Grifols. Infliximab measurements across all kits were affected by interference from antibodies to infliximab (ATI). This study identified the Lisatracker kit as the most accurate in quantifying infliximab levels, although it was limited by false positive results at low concentrations of infliximab as well as interference from ATI. This has important implications for the monitoring and management of patients receiving infliximab therapy.