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The VWF multimer assay by Sebia is easy to perform and can be successfully implemented in any clinical laboratory for second-stage evaluation of VWD. The resolution power of multimer distribution is adequate to correctly classify VWD types 1, 2A, 2B, and 3.

Regulation of binding between von Willebrand factor (VWF) and the platelet receptor glycoprotein (GP) Ibα is one of the key steps in controlling hemostasis and thrombosis. On vascular injury at sites of high shear rates, the GPIbα interaction with subendothelial-bound VWF will initiate the tethering of circulating platelets to the vessel wall. Tethered platelets subsequently roll on the damaged vessel wall, a process that is amplified by the activation of the platelet integrin αΙΙbβ3 (GPIIb/IIIa). The initial tethering to VWF is rapidly followed by platelet binding to collagen through specific receptors (GPVI and α2β1), leading to firm adhesion, activation, and additional stable bonds mediated by αΙΙbβ3. The above described interactions can result in two distinct processes: physiological hemostasis and pathological thrombosis. Furthermore, VWF carries coagulation factor VIII, which is involved in thrombin formation that in addition to activating platelets, mediates fibrin formation and has several other actions. The importance of VWF in hemostasis is well known in patients suffering from von Willebrand disease (VWD) who present with a defect in both platelet plug and fibrin formation. Type 2B VWD is of special interest as it may provide further insight into the mechanism by which VWF promotes the adhesion of platelets to a thrombogenic surface under conditions of high shear stress. The variant phenotypic manifestations in patients affected with type 2B VWD, however, have raised the question of locus heterogeneity in VWD as a consequence of, for example, additional defects in receptor or signaling proteins mediating platelet adhesion and aggregation. Indeed, quite a few polymorphisms of platelet receptors have been associated with increased bleeding in VWD. However, many aspects of the disease remain to be elucidated. For instance, thrombin and platelet procoagulant activity may be important counterplayers to determine the severity of the bleeding complications associated with VWD.

Introduction The thrombin generation assay‐calibrated automated thrombogram (TGA‐CAT) method is used to measure the overall coagulation capacity in plasma. However, the method is still considered to be a research tool, mainly because of its’ lack of standardization. Aim Our study aimed to further raise the standardization level for the TGA‐CAT method by evaluating a detailed standardization protocol and three reference plasmas’ (RP)s ability to normalize results. Methods Six Nordic centres participated in the study, and with input from all centres a detailed laboratory standardization protocol based on the TGA‐CAT manual of the manufacturer was established. Three types of plasma, hypo‐,normal and hypercoagulable plasma were assessed. Three commercial lyophilized RPs were used for normalization of data. All samples were aliquoted at the Malmö centre and sent frozen at −20˚C to participating centres. Results Before normalization, all results under all testing conditions showed inter‐laboratory coefficient of variability of 10% or lower except for endogenous thrombin potential (12%) and peak (14%) in hypo‐plasma with 1 pmol/L tissue factor as starting agent. Successful normalization, improving variability in results, was obtained with two of the three evaluated RPs (HemosIL RP and Affinity RP). Conclusion With our standardization concept, we were able to produce TGA‐CAT results as robust as standard coagulation assays used in the routine laboratories. Normalization with HemosIL RP may be considered in populations with low or unknown coagulability, while when analysing plasma samples from populations where hypercoagulability is known or suspected, normalization with Affinity RP may be preferred.

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