VWF and Von Willebrand disease: Aggregation of platelets evoked by ristocetin is dependent on conformational changes of von Willebrand factor facilitating the protein interaction with GPIb-IX-V receptor (Kang et al., 2008; Obert et al., 2014) and that is why, ristocetin-induced platelet aggregation (RIPA) test was used to a diagnosis of von Willebrand disease (Horvath et al., 2004; Ruggeri, 2007; Castaman et al., 2014).