Evaluation of chromogenic factor IX assays by automated protocols.

INTRODUCTION: Chromogenic substrate assays (CSA) to measure Factor IX (FIX) have recently become commercially available. However, information on their performance characteristics and use in diagnostic haemostasis laboratories remains limited.

AIM: To evaluate the Hyphen Biomed (Hyphen) and Rossix FIX CSAs on fully automated coagulation analysers and compare them to the FIX one-stage assay (OSA). This study was conducted in a tertiary referral haemostasis laboratory associated with a haemophilia treatment centre.

METHODS: Automated CSA protocols were adapted to the Sysmex CS2500 (CS2500) and Diagnostica Stago STA-R (STA-R) analysers. Samples assayed were from healthy volunteers, haemophilia B patients and FIX deficient plasma spiked with either plasma derived, recombinant or extended half-life FIX products.

RESULTS: Reference intervals for Hyphen and Rossix assays were 73 IU/dL to 164 IU/dL and 73 IU/dL to 168 IU/dL, respectively, on the CS2500 analyser; and 84 IU/dL to 165 IU/dL for the Rossix assay on the STA-R. Repeatability across all method/analyser combinations resulted in CVs ranging from 0.8% to 5.4%. Between run reproducibility gave CVs <6.7% for all method/analyser combinations. In spiked samples, FIX recoveries were mostly within an acceptable limit of 100 ± 25% for BeneFIX® , Rixubis® and Alprolix® with some differences between CSAs.

CONCLUSION: Both commercial factor FIX CSA kits can be adapted for Stago and Sysmex automated coagulation analysers. Reagent cost and workflow practices will need to be considered. These assays are potentially more consistent than OSA in measurement of replacement FIX products in haemophilia B patients.