# Measurement of Anti-TNF Biologics in Serum Samples of Pediatric Patients: Comparison of Enzyme-Linked Immunosorbent Assay (ELISA) with a Rapid and Automated Fluorescence-Based Lateral Flow Immunoassay

## TL;DR

This study compares a new rapid test with the traditional ELISA method for measuring anti-TNF drugs in children's blood, finding the new test is fast and accurate enough for clinical use.

## Contribution

The study introduces and validates a rapid fluorescence-based immunoassay for measuring anti-TNF drug levels in pediatric patients.

## Key findings

- AFIAS showed strong correlation with ELISA for IFX (rho 0.98) and moderate for ADL (rho 0.83).
- AFIAS results had acceptable bias and agreement for IFX but wider limits for ADL.
- AFIAS did not provide sufficient data for anti-IFX antibody correlation.

## Abstract

Background: Therapeutic drug monitoring (TDM) of infliximab (IFX) and adalimumab (ADL) mainly relies on the use of enzyme-linked immunosorbent assays (ELISA). More recently, rapid assays have been developed and validated to reduce turnaround time (TAT). Here, we compared IFX and ADL concentrations measured with both ELISA and a new fluorescence-based lateral flow immunoassay (AFIAS). Methods: In serum samples from pediatric patients, IFX and ADL drug levels, and total anti-IFX antibodies were measured using clinically validated ELISA kits (Immundiagnostik AG). Samples were further analyzed using a new rapid assay (AFIAS, Boditech Med Inc.) to measure drug levels and total anti-IFX antibodies. Results: Spearman’s correlation coefficients (rho) were 0.98 [95% confidence interval (CI) 0.97 to 0.99] for IFX (p < 0.001) and 0.83 (95% CI 0.72 to 0.90) for ADL (p < 0.001). Calculated % bias was −14.09 (95% Limits of agreement, LoA, −52.83 to 24.66) for IFX and 15.79 (LoA −37.14 to 68.73) for ADL. For the evaluation of total anti-IFX antibodies, we did not collect sufficient data to establish a statistically significant correlation between AFIAS and ELISA. The inter-rater agreement showed a “substantial” and a “moderate” agreement for IFX and ADL, respectively. Conclusions: Our results show that the AFIAS assay has an accuracy and analytical performance comparable to that of the ELISA method used for TDM of IFX and ADL. Therefore, the introduction of this device into routine clinical practice could provide results more quickly and with similar accuracy as ELISA, allowing clinicians to rapidly formulate clinical decisions.