Kitchen, Steve

AbstractThis guidance document has been prepared on behalf of the International Council for Standardisation in Hematology. The aim of the document is to provide guidance and recommendations on the measurement of factor VIII (FVIII) and factor IX (FIX) inhibitors. After an introduction on the clinical background and relevance of factor VIII and factor IX inhibitor testing, the following aspects of laboratory testing are included: screening for inhibitors, assay principle, sample requirements, testing requirements and interpretation, quality assurance, interferences and recent developments. This guidance document focusses on recommendations for a standardised procedure for the laboratory measurement of FVIII and FIX type I inhibitors. The recommendations are based on published data in peer‐reviewed literature and expert opinion.

Abstract Introduction: Differences in coagulation assay reagents may lead to variable results for some extended-half-life (EHL) recombinant factor VIII (rFVIII) products, with the potential to adversely affect patient care. Laboratories assessing EHL-rFVIII activity can choose from many available one-stage assay and chromogenic assay reagents. A field study was conducted to evaluate the ability of clinical laboratories to accurately measure FVIII activity in plasma samples spiked with BAY 94-9027, an EHL rFVIII, when using diverse assay reagents and when guided in the choice of reagent. In a regional subanalysis, BAY 94-9027 field study results from clinical laboratories in the United States and Canada were compared with those from Europe and Israel. Methods: In this 2-part study, a broad range of laboratories in the United States, Canada, Europe (Austria, Germany, Italy, Romania, Spain, Switzerland, United Kingdom), and Israel were provided samples containing defined concentrations of BAY 94-9027 or an unmodified rFVIII (antihemophilic factor [recombinant] plasma/albumin-free method [rAHF-PFM]) as a control. In part 1, each laboratory measured FVIII activity using their routine methods (one-stage assay, chromogenic assay, or both); laboratories that had ≥2 routine one-stage assays were asked to perform sample testing with one of the less commonly used assays in the laboratory to ensure that part 1 captured both the prevalence and heterogeneity of one-stage assays used in the geographic regions studied. In part 2, laboratories used one-stage assays with SynthASil and Pathromtin SL reagents provided by Bayer; SynthASil and Pathromtin SL have previously been shown to accurately measure BAY 94-9027 and full-length rFVIII products. The field study data were analyzed to identify the most commonly used reagents in the 2 regions (United States/Canada and Europe/Israel) and to assess if regional differences resulted in differences in accuracy of FVIII activity measurement. Results: 52 laboratories (US/Canada, n=25; Europe/Israel, n=27) participated in the field study. The one-stage reagent SynthASil was commonly used in all countries (n=15) in part 1, but differences were seen in the frequency of use of other reagents. PTT-A (n=6) and Actin FSL (n=5) were frequently used in the US/Canada and Actin FS (n=6) and Pathromtin SL (n=6) in Europe/Israel. Regional differences in the choice of assay, with US/Canada more likely to use assays that did not accurately measure BAY 94-9027, affected the ability of laboratories to accurately measure FVIII activity in the spiked samples (Figure). In part 1 of the study, regional differences in median recovery of BAY 94-9027 were seen among laboratories when using their own in-house one-stage assays. These differences were not seen in part 2 of the study when laboratories used provided reagents (SynthASil and Pathromtin SL), despite using the same instrumentation as used in part 1. Regional differences in part 1 might have been exacerbated by use of less common, and potentially inappropriate, one-stage assay reagents, affecting the accuracy of BAY 94-9027 measurement. Chromogenic assay use was more common in Europe/Israel (n=11) than US/Canada (n=5). No regional differences in chromogenic assay results were observed. Conclusions: Most clinical laboratories were able to accurately measure BAY 94-9027 activity using their in-house assays. However, regional differences in the accurate measurement of BAY 94-9027 activity were influenced by regional choice of one-stage reagents used in part 1 of the study; the activity and accuracy differences were eliminated when all laboratories used the same provided one-stage reagents with their in-house instruments (part 2 of study). Therefore, standardization of laboratory procedures and use of newer, more accurate one-stage assay reagents should improve measurement of FVIII activity with EHL products. Figure. Figure. Disclosures Castellone: Bayer: Membership on an entity's Board of Directors or advisory committees; Wilmer-Hale: Consultancy. Church:Bayer: Employment. Leong:Bayer: Employment. Kitchen:Bayer: Consultancy, Other: travel reimbursement, Speakers Bureau.