Background: Several different plasma-derived and recombinant von Willebrand Factor (VWF) concentrates are used to prevent and treat bleeding in von Willebrand disease patients. Measuring VWF antigen levels and VWF activity can be useful in monitoring replacement therapy however several different assays could exist for measuring these parameters.

Aims: The aim of this study was to assess the performances of different laboratory assays in monitoring VWF replacement therapy using 3 plasma-derived and 1 recombinant VWF concentrates.

Methods: Human VWF deficient plasma (Cryopep®) was alternatively spiked with four different concentrates of VWF (plasma-derived : Eqwilate® (Octapharma®), Wilfactin® (LFB®), Voncento® (CSL Behring®); and recombinant : Veyvondi® (Takeda®) ) and human standard plasma (Siemens®). We measured VWF antigen (VWF:Ag) and different VWF activities using 4 different analyzers: VWF:Ag and VWF:GPIbR (HemosIL®) on AcuStar and ACL-Top (Werfen®), VWF:CB (HemosIL®) on AcuStar, VWF:Ag and VWF:Rco on STAR-Max (Stago®), VWF:Ag and VWF:GpIbM (Innovance®) on CS-2100i (Sysmex®). Assays were performed in triplicates using 4 different final concentrations of VWF (1, 0.5, 0.25 and 0.1 IU/mL).

Results: For all VWF concentrates tested, there was no significant difference between techniques when measuring VWF:Ag at all 4 concentrations.
Except for human standard plasma for which inter-assay variability showed high agreement (Fig.1), results for VWF activity measurements showed variations depending on the assay and molecule tested.
Wilfactin® activity levels were significantly higher with ACL-Top than all 4 other assays especially at high concentrations (Fig.1 Fig.2). VWF:GpIM and VWF:Rco assays showed significantly lower activity levels than the target in plasma spiked with Wilfactin®, Voncento® and Eqwilate® (p< 0.05).
For Veyvondi® no agreement was found between all assays at every concentration tested (p< 0.05).
Of note, VWF:CB was consistently higher whereas VWF:Rco provided the lowest results.

Conclusions: VWF activity assays are not all equivalent when monitoring different VWF concentrates and precautions should be taken accordingly.

[Figure1: VWF activity measured for 1 IU/mL final concentration of VWF]

[Figure 2: VWF activity measured for 0.5 IU/mL final concentration of VWF]

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/monitoring-recombinant-and-plasma-derived-vwf-concentrates-an-in-vitro-study/