Background. The von Willebrand factor activity (VWF:Ac) assay is important in the diagnosis of von Willebrand disease (VWD), but the availability of this test is limited, because manufacturers of analyzers may not offer a possibility to measure VWF:Ac. Thus fully automated VWF:Ac system comprising reagents and analyzer by different manufacturers was implemented and verification of this ristocetin independent assay was done.
Methods and materials. The INNOVANCE® VWF Ac (Siemens Healthcare Diagnostics, Germany) kit was adapted on STA-R Evolution (Diagnostica Stago, France). Calibration was done with Standard Human Plasma, inter- and intra-assay precision was estimated with 2 levels of commercial QC material - Control Plasma N and P (all from Siemens Healthcare Diagnostics, Germany). Randomly selected residual patient plasmas were analyzed in paralel by 2 commercial kits (HemosIL vWF:RCo and HemosIL vWF:Ac assays on automated coagulometer ACL TOP500 (both reagents and analyzer by Instrumentation Laboratory, USA)) and results compared. Storage conditions of -20 °C were evaluated.
Results. Intra- and inter-assay variability ranged 4.00-5.02% and 4.69-5.00% respectively. Fresh and frozen thawed plasma VWF:Ac results correlated (r2=0.952) and difference was not significant (p=0.201). VWF:Ac results of implemented assay and 2 HemosIL assays were comparable (vWF:Ac r2=0.984; vWF:RCo r2=0.978) and difference was not significant (p=0.222 and p=0.835 respectively).
Conclusions. The analytical performance of implemented VWF:Ac assay was shown to be acceptable. Thus VWF:Ac assay can be easily obtained by implementing it on different manufacturer's analyzer by adapted protocol and can be used for the diagnosis, classification of VWD and monitoring VWD therapy.