[Factor IX assays in treated hemophilia B patients].

Replacement therapy with plasma-derived or recombinant FIX (pdFIX or rFIX) concentrates is the standard of treatment in patients with hemophilia B. The method predominantly used for measuring factor IX (FIX:C) levels is the one-stage clotting assay (OSA) but this method depends on the activated partial thromboplastin time (APTT) reagent and the coagulation analyzer used, and wide variations in the measurements of FIX recovery have been reported with some factor concentrates. The French study group on the biology of hemorrhagic diseases (a collaborative group of the GFHT and MHEMO network), presents a review of the literature and proposals for the monitoring of FIX:C levels in treated hemophilia B patients. The use of OSA calibrated with a plasma reference tested against the current FIX WHO International Standard is recommended for the monitoring of patients treated with pdFIX or rFIX. Chromogenic substrate assays (CSA) are adequate for the monitoring of patients treated with Rixubis