Background Golimumab (GLM) is a fully human monoclonal antibody to TNFa and it is an inhibitor that binds to both transmembrane and soluble bioactive human TNFa and blocks their action. This TNF-inhibitor is used in the treatment of the rheumatoid arthritis (RA), ankylosing spondilitis (AS) and psoriatic arthritis (PsA). Recently it has been reported that there exists a significant relationship between GLM levels circulating in serum and the patients' response. Therapeutic drug monitoring (TDM) with serum level measurement can be a useful tool to optimization of the anti-TNF treatment, but the lack of standardization can hinder the comparison.
Objectives To determine the correlation and agreement between two different Enzyme-Linked Immunosorbent Assay (ELISA) assays for measuring golimumab.
Methods A total of 121 sera from a cohort of 44 patients under golimumab treatment with different rheumatic diseases (RA, AS and PsA) were analyzed. The golimumab trough levels were analyzed at the beginning of the treatment and every 6 months to 2 years of treatment. The serum levels were analyzed in blind manner by the Immunology Unit from the La Paz University Hospital (Madrid, Spain) using the commercial Kit Promonitor®-GLM (Progenika, Biopharma SA, Derio, Vizcaya) and by Sanquin Diagnostic Services (Amsterdam, The Netherlands) using an own developed ELISA. The statistical analysis to quantify the correlation and the agreement between GLM levels were made with SPSS version 20 (IBM, New York, NY, USA) and with GraphPad Prism version 6.0 for Windows (GraphPad Software, San Diego, CA, USA).
Results The correlation between GLM levels of the different two assays was r Pearson of 0.963 (p<0.001). Qualitatively, GLM levels were detected in only one serum with the Sanquin assay whereas in the Promonitor®-GLM this serum was negative. The agreement between GLM levels of the two different assays was analyzed using an intraclass correlation coefficient (ICC). We obtained an ICC =0.96 (95% CI 0.944-0.972; p<0.001). These data were represented by a Bland-Altman plot (fig.1) where we obtained an average of differences of 25.56 with a 95% limit of agreement (-570.2 - 621.3), indicating that the two assay methods produce similar results.
Conclusions There is an excellent correlation and agreement between GLM levels obtained with the commercial Kit Promonitor®-GLM and the levels obtained in the Sanquin laboratory, both of them with ELISA technology. These results may help us to standardize the GLM levels and the comparisons between different data reported with either of these two assays.
Disclosure of Interest None declared
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