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Letter: detection of infliximab levels and anti‐infliximab antibodies — comparison of three different assays

SIRS, We refer to the publication written by N. Vande Casteele et al., which determined the correlation between three different immunoassays for measuring infliximab and ATI (antibodies to infliximab). We formally contest the conclusion of this article, in which the authors conclude that Theradiag (bmd) LISA TRACKER Premium immunoassay detected 18% of false-positive samples for the assay of infliximab drug level. The Theradiag (bmd) LISA TRACKER Premium immunoassay was performed by the team of Groningen (Department of Hospital and Clinical Pharmacy). The kit lot numbers used by the laboratory of Groningen were LTI 051101 and LTI 111001. We were informed of the discrepant results through the oral presentation given by Leuven team (Laboratory for Pharmaceutical Biology) during the European Immunogenicity Platform congress in February 2012 and further released on the web. Thanks to the collaboration of the teams of Groningen and Sanquin Diagnostics, we had the opportunity to get 8 of 11 discrepant sera (three of them were no longer available) from the published study. The eight sera were tested and repeated independently on the same reference lot numbers LTI 051101 and 111001, like those used by the laboratory in Groningen. Results are presented in the graph below and clearly invalidate the data published by showing no false-positive result. The assay validation criteria (OD value from highest standard point and positive control value) being in compliance with the assay handling by Groningen, we suspect an issue occurring during the pre-analytical processing of the samples. Our kits are CE marked and therefore meet strictly the performance requirements (sensitivity, specificity among others) requested by the European directive 98/97/CE. So far our LISA TRACKER users have published their results in several journals, and numerous scientific publications (PhD theses and posters) were also presented to various international congresses. Our immunoassays are used for routine diagnostic purposes in several European laboratories. As of today, we have not received any other reports of false positive tests. Moreover, we have recently completed a correlation on 22 new samples, kindly provided by the laboratory of Leuven, between our commercialised assay and their laboratory developed test. We are open for any scientific collaboration or complementary studies with the teams concerned in order to clarify the reasons why they have obtained and published non-validated discrepant results with our immunoassays.