Background: Several clinical laboratory methods have been established to measure plasma-derived von Willebrand factor (pdVWF) in plasma samples, but few data are available on their use for analyzing recombinant VWF (rVWF).

Aims: Evaluate how clinical/diagnostic laboratories analyze pdVWF and rVWF in vitro.

Methods: Human VWF-deficient plasma samples (HRF Inc., Raleigh, NC, USA) were spiked with rVWF or pdVWF (antihemophilic factor/VWF complex [human]), each at final concentrations of 1.0, 0.6, 0.2, 0.1 IU/mL von Willebrand factor:ristocetin cofactor activity [VWF:RCo] according to labeled VWF activity. The SSC/ISTH secondary coagulation standard lot #5 was used as a control. Participating laboratories received 3 sets of these blinded aliquots and assayed each set in an independent run. The mean results per assay were compared with the expected potency based on labeled activity of the drug. Microsoft Excel v16.0 and Minitab 20.4 were used for data arrangement, graphical visualization, and statistical analyses.

Results: Samples were analyzed by 22 laboratories from 11 countries (North America, n=5; Europe, n=16; India, n=1). Depending on assay type, variability between laboratories was high, particularly for VWF:RCo activity. Geometric mean recovery of VWF:RCo for rVWF was acceptable (78–112% relative to labeled VWF:RCo target); measured pdVWF concentrations were significantly off-target, with lower values (51–104%). For both products, high recovery of VWF antigen content with acceptable precision was achieved versus labelled VWF:RCo activity (109–122%) (Table 1). VWF platelet receptor glycoprotein Ib (GPIb) assays gave high recovery for rVWF (114–125%) and low recovery for pdVWF (62–74%). VWF collagen-binding assays gave similar results to GPIb methods (Table 2).

Conclusion(s): This in vitro study indicates that the results of VWF assays used in clinical laboratories differ between rVWF and pdVWF, particularly for GPIb assays. These differences may arise from the higher multimeric structure of rVWF and should be considered when analyzing post-infusion samples from patients treated with either product.

Table 1

Table 1. Recovery of rVWF and pdVWF in VWF-deficient plasma using the VWF:Ag and VWF:RCo assays

Table 2

Table 2. Recovery of rVWF and pdVWF in VWF-deficient plasma using the VWF:GPIb and VWF:CB assays

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/in-vitro-field-study-assessing-how-clinical-hemostasis-laboratories-analyze-recombinant-and-plasma-derived-von-willebrand-factor-products/