Detection of adalimumab and antibodies to adalimumab using a homogeneous mobility shift assay

In 2013 a novel commercial test was launched (Anser ¹ ADA test) for the assay of serum adalimumab (ADL) and antibodies to adalimumab (ATA). This study aims to understand clinical practice patterns used with ADL in a real-world cross-sectional population.

Wilcoxon rank sum test, and linear and logistic regression methods were applied in the statistical analysis to test hypotheses. The study design was observational and uncontrolled.

Of a total of 14,239 tests conducted, 5509 had information available that pertained to reasons for ordering, of which disease monitoring (46.9%) was the most common. Median serum ADL level with standard maintenance dosing (40 mg, biweekly) was 8.8 μg/mL (n = 2901). A five-fold decrease in median serum ADL levels occurred with very low ATA titers (1.7-3 U/mL, p < .0001). Serum ADL levels decreased further with ATA >7 U/mL (p < .0001). A total of 16.5% of patients were ATA positive, of whom 61.9% had low ATA (1.7-7 U/mL); 87.9% of ATA-positive patients had serum ADL levels ≤4.4 μg/mL. Expression of inflammatory markers significantly increased with high ATA (>7 U/mL). An inverse relationship between ADL and ATA was observed (R²: 0.49), and 4.1 μg/mL was identified as a cut-off that may segregate ATA-positive patients.

In this real-world cross-sectional population, serum ADL levels decreased with increasing ATA titers, with low ATA titers (≤7 U/mL) significantly reducing serum ADL compared to ATA-negative samples. Expression of inflammatory markers significantly increased at higher ATA titers (>7 U/mL). These findings highlight the clinical importance of monitoring patients for drug levels and anti-drug antibody titers.