Clinical Implications of Point-of-Care Measurement of Adalimumab Concentration and Anti-Adalimumab Antibodies in Patients with Rheumatoid Arthritis and Ankylosing Spondylitis

To evaluate the analytical performance and clinical utility of the automated fluorescence-based POC immunoassay system (AFIAS), compared with established enzyme-linked immunosorbent assay (ELISA) methods for measuring adalimumab and anti-adalimumab antibodies (AAAs) in patients with rheumatoid arthritis and ankylosing spondylitis. 96 patients receiving adalimumab for rheumatoid arthritis (RA) or ankylosing spondylitis (AS) were consecutively recruited. Measurements of adalimumab trough levels and AAAs were taken before the patients' scheduled adalimumab injection. Three ELISA techniques (RIDASCREEN^®, IDKmonitor^®, and LISA TRACKER) were compared with the AFIAS method. Statistical analyses included Bland-Altman, Passing-Bablok regression, kappa values, and intraclass correlation coefficients. Clinical and demographic characteristics were examined to determine the association between adalimumab concentration and AAA detection. The diagnoses included 58 RA diagnoses and 38 AS diagnoses. The median concentrations were 9.33, 7.4, 7.4, and 9.38 µg/mL for RIDASCREEN, IDKmonitor, LISA TRACKER, and AFIAS, respectively. Strong correlations were observed between the techniques. Bland-Altman analysis revealed bias differences of 0.85, 2.03, and 2.76 µg/mL, and the Passing-Bablok regression slopes were 1.046, 1.391, and 1.274 for RIDASCREEN, IDKmonitor, and LISA TRACKER, respectively, compared with AFIAS. Agreement in AAA detection showed kappa values of 0.81 and 0.75 for AFIAS versus IDKmonitor and LISA TRACKER, respectively. A high body mass index, extended injection interval, and RA diagnosis were associated with low adalimumab concentrations in the multivariate analysis. Antinuclear antibody positivity, a higher rheumatoid factor, and disease activity were associated with AAA positivity in univariate analysis. The AFIAS POC measurement method demonstrated time-efficient and highly agreeable results for adalimumab and AAA measurements compared with the results of commercial ELISA methods.