Three Rossix posters at ISTH in Melbourne

PB0099 Evaluation of Lupus Anticoagulant interference in a chromogenic Factor IX kit for determination of Factor IX activity. P Bryngelhed, R Hengeveld, C Klopper-Tol, F Ehklas, S Rosén, AK Stroobants

Rossix collaborated with Amsterdam UMC to evaluate the Lupus anticoagulant interference in the Rox Factor IX kit method. It was concluded that the Rox Factor kit can be safely used for determination of FIX activity in plasma from Lupus Anticoagulant positive patients.

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PB1294 Assessment of Factor IX Padua activity with a one-stage clotting method and with FXIa- and tissue factor/FVIIa-based chromogenic methods. S Rosén, P Bryngelhed, C Bulato, P Simioni

The Factor IX (FIX) Padua variant is currently explored both in recombinant therapy and gene therapy projects. FIX Padua shows up to 8-fold higher activity vs wild-type FIX in one-stage methods whereas there are limited data available with chromogenic substrate (CS) methods.

The potency assignment of Factor IX Padua was assessed with a one-stage method (Actin FS), FXIa-based chromogenic method (Rox Factor IX) and a Tissue Factor/FVIIa-based chromogenic method in collaboration with the Department of Medicine at the University of Padua Medical School.

Conclusions

• The specific activity (FIX:C/FIX Ag) of FIX Padua with Rox Factor IX was >3-fold higher than for wtFIX but only about 40% vs Actin FS (FIX:C/FIX:Ag about 8.5).
• A TF/FVIIa based method showed a specific activity for FIX Padua of about 3.9, in fair agreement with Rox Factor IX.
• The ratio of FIX Padua activity vs wtFIX was not affected over an 11-fold increased FXIa concentration in the Rox Factor IX method.
• Both chromogenic and one-stage methods can be used to determine FIX Padua activity. Further studies are required to elucidate causes of method discrepancies.

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PB1295 Recombinant Factor IX fused with albumin (rFIX-HSA) is underassigned by one-stage methods with silica as contact activator. S Rosén, P Bryngelhed

 One-stage methods show in general considerably lower rFIX-HSA potency than chromogenic substrate methods. The cause(s) of the discrepancy was previously not known, and the aim of the work was to investigate the causes of discrepancy on rFIX-HSA potency assignment by OS methods and a CS method by use of new variant OS methods.

Conclusions:

• rFIX-HSA potency is underassigned in OS methods using APTT reagents with colloidal silica as contact activator, most likely due to attenuated activation and hence deviation from like-vs-like behavior compared to a pdFIX concentrate standard.
• Variant OS methods with Phospholipid-TGT and a platelet like PL composition with no contact activator and with FXIa included with CaCl₂ give results in line with Rox Factor IX.
• pdFIX potency is similar with all OS methods and with Rox Factor IX, thus displaying like-vs-like behavior to a pdFIX concentrate standard.

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