Comparison between monotest and traditional batch-based ELISA assays for therapeutic drug monitoring of infliximab and adalimumab levels and anti-drug antibodies.

Objectives: To compare a new ready-to-use monotest immunoassay, CHORUS Promonitor, for the quantification of serum biological drug levels and anti-drug antibodies of anti-TNF agents, against the reference batch-based ELISA test, Promonitor.

Methods: Blood samples were collected from patients treated with anti-TNF agents, infliximab (IFX) or adalimumab (ADL). IFX and ADL levels, as well as anti-IFX and anti-ADL antibodies were quantified and compared between the standard ELISA reference test, Promonitor, and the automated monotest ELISA assay, CHORUS Promonitor. Data analysis included both qualitative and quantitative comparison between both tests. For the qualitative comparison, overall percent agreement (OPA) was calculated. For the quantitative comparison, Passing-Bablok regression analysis and Bland-Altman analysis were used.

Results: For IFX and ADL levels, the qualitative overall agreement between methods was 100 % (Cohen's coefficient=1). For anti-IFX and anti-ADL antibodies, OPA was 98.8 % and 97.3 %, respectively. Quantitative comparison indicated a very strong correlation between both assays: IFX (r=0.97, n=74), ADL (r=0.95, n=54), anti-IFX (r=0.93, n=72), and anti-ADL (r=0.97, n=61). The regression analysis determined an excellent comparability of drug levels between methods. Bland-Altman analysis showed a bias difference between assays of 6 % for IFX, 0 % for ADL, 24 % for anti-IFX, and 14 % for anti-ADL.

Conclusions: Monotest CHORUS Promonitor was a reliable assay to quantify IFX, ADL, anti-IFX and anti-ADL in samples with comparable results to those obtained with the reference batch-based ELISA technique.