Comparative Analysis of 2 Commercially Available Assays for Therapeutic Drug Monitoring of Infliximab and Adalimumab

Tumor necrosis factor is a crucial proinflammatory cytokine in immune-mediated diseases. Tumor necrosis factor inhibitors (TNFi), such as infliximab and adalimumab, effectively treat rheumatological and digestive disorders. However, challenges such as primary nonresponse, secondary treatment failure, or adverse reactions limit their efficacy. Monitoring TNFi levels is essential for optimizing treatment and improving outcomes. An enzyme-linked immunosorbent assay (ELISA; Promonitor) was compared with 2 commercially available methods for quantifying infliximab and adalimumab levels: the chemiluminescence assay (i-Track10) and fluorescence assay (Afias-10).

Serum samples from 166 patients with inflammatory bowel disease were analyzed. Drug levels were measured using i-Track10, Afias-10, and Promonitor. Spearman's correlation analysis, Bland-Altman analysis, analysis of differences, Passing-Bablok regression, and Cohen kappa for agreement assessment were used for statistical analysis.

Strong correlations were observed between Promonitor and Afias-10 for infliximab (rs = 0.982) and adalimumab (rs = 0.972), and with i-Track10 (rs = 0.935 for infliximab, rs = 0.947 for adalimumab). However, significant differences indicated noninterchangeability with ELISA. Passing-Bablok regression showed systematic and proportional biases. Cohen kappa exhibited higher concordance with Afias-10 for therapeutic ranges (κ = 0.962 for infliximab, κ = 0.849 for adalimumab) compared with i-Track10.

Afias-10 and i-Track10 are suitable for TNFi monitoring but are not interchangeable with ELISA. Consistent assay methods should be used for patient monitoring to ensure accuracy and reliability.