Validation of the i-Tracker Drug and Total Anti-Drug Antibody CLIA Assays on IDS-iSYS for Therapeutic Drug Monitoring in Adalimumab- and Infliximab-Treated Patients

<b>Background/Objectives</b>: Adalimumab and Infliximab are biologics used to treat autoimmune diseases. Monitoring drug and anti-drug antibody (ADA) levels in patients helps optimize treatment. However, current quantitation methodologies for drug and total (free and drug-bound) ADAs often involve multi-step workflows. Automated systems can streamline the process. The i-Tracker chemiluminescent immunoassays (CLIA) are cartridge-based kits for quantifying serum levels of drugs such as Adalimumab, Infliximab, and associated ADAs. Herein, we aimed to establish performance characteristics of the i-Tracker Adalimumab, Infliximab, and total ADAs in serum on the random-access analyzer IDS-iSYS and to compare patient results with an electrochemiluminescent immunoassay (ECLIA)-based reference method. <b>Methods</b>: Remnant serum specimens, calibration material, or spiked serum were used to evaluate assay linearity, precision, functional sensitivity, and accuracy on the IDS-iSYS analyzer and to perform the method comparison. <b>Results</b>: The assays displayed linearity, accuracy, and up to 8% imprecision across clinically relevant analyte ranges. Compared to the reference method, the drug assays exhibited a strong linear fit (correlation coefficient > 0.95) with <±1.0 µg/mL mean bias. The total anti-Adalimumab assay demonstrated over 85% qualitative agreement. The total anti-Infliximab assay, however, showed higher detection rate of ADAs in Infliximab-treated patient specimens, yielding < 60% negative agreement with the reference method. Although i-Tracker total ADA assays exhibited drug sensitivity, they still detected ADAs in supratherapeutic drug concentrations. <b>Conclusions</b>: The i-Tracker assays demonstrated robust analytical performance, suggesting potential for clinical application. The method comparison underscored functional differences with the reference method, an important consideration when transitioning assay formats for monitoring Adalimumab- and Infliximab-treated patients.