Platelet-dependent von Willebrand factor activity. Nomenclature and methodology: communication from the SSC of the ISTH - Bodó, I; Eikenboom, J; Montgomery, R; Patzke, J; Schneppenheim, R; Di Paola, J; von Willebrand factor Subcommittee of the Standardization and Scientific Committee of the International Society for Thrombosis and Haemostasis (J Thromb Haemost, 2015)