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Influence of aPTT reagents on the 1-stage clotting assay activity in human plasma determined for recombinant FIX products

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Influence of aPTT reagents on the 1-stage clotting assay activity in human plasma determined for recombinant FIX products

Herbert Gritsch, Stefan Romeder-Finger, Friedrich Scheiflinger, Peter L. Turecek

Baxter Innovations GmbH, Vienna, Austria

Introduction

RIXUBIS is a new recombinant factor IX (FIX) product produced from CHO cells using the protein-free manufacturing technology. Potency assignment is performed with a one-stage clotting assay (OSCA) based on the activated partial thromboplastin time assay (aPTT). The test is calibrated against the 4th WHO IS for FIX  concentrates. RIXUBIS and another rFIX product were analyzed for FIX activity using a panel of aPTT reagents from various manufacturers and with chromogenic assays. Results were compared with the labeled potency. The impacts of type and source of the aPTT reagent were investigated.

Summary & Conclusions

•Potency assignment for both recombinant FIX products is dependent on the type and composition of the aPTT reagent used
•The impact of various aPTT reagents on one-stage clotting activity is very similar for both products; differences up to 40% were observed
•The chromogenic FIX activity of RIXUBIS is in good agreement with the labeled FIX potency while for the other rFIX product lower chromogenic FIX activities are found
•Labeling strategy for RIXUBIS prevents from overestimation of FIX activity and lowers the risk of underdosing hemophilia B patients
•Reagent-dependent variation in in-vitro recovery in FIX-deficient plasma is similar for both rFIX products