Performance of a New Rapid Point-of-Care Test for Infliximab Levels in Patients with Inflammatory Bowel Disease: A Comparison to ELISA

Background Therapeutic drug monitoring of infliximab levels in patients with inflammatory bowel disease (IBD) optimizes patients’ treatment. The reference technique is based on enzyme-linked immunosorbent assay (ELISA) although point of care (POC) assays are being developed. Aims To assess the performance of a new rapid immunochromatographic POC assay (Promonitor Quick IFX) compared with ELISA technique to measure infliximab levels in patients with IBD. Methods A prospective, observational, unicentric study was performed on capillary blood samples from patients with IBD before infliximab infusion (trough levels). Infliximab levels and anti-infliximab antibodies were measured using the ELISA technique (Promonitor IFX) and the POC assay. Correlation between both techniques was assessed by Pearson’s coefficient. Quantitative differences were evaluated by Bland–Altman analysis. Samples were stratified according to infliximab therapeutic ranges (< 3 μg/mL, 3–8 μg/mL, and > 8 μg/mL). Results A total of 135 experimental samples were assessed. Infliximab levels showed a high correlation between POC and ELISA tests ( r = 0.84, P < 0.001). The mean difference between tests was 1.46 μg/mL ( P < 0.001), being minimal for concentrations < 8 μg/mL. POC and ELISA assays showed an overall concordance of 87.4%. Most samples were in the same therapeutic range, which lead to equivalent therapeutic decisions. POC and ELISA assays detected the presence of anti-infliximab antibodies in 2.2% and 3.7% of the samples, respectively. Conclusions POC assay results in blood samples from patients with IBD were comparable to those obtained with the reference ELISA technique. The POC assay could be considered for routine testing based on its ease of use and rapidity.