Furthermore, GpIb and VWF are also necessary for platelet-to-platelet cohesion [2]. Aggregation of platelets within the growing haemostatic plug is promoted by the interaction with a second receptor on platelets, the GpIIb/IIIa (or integrin αIIbβ3) which after activation binds to VWF and fibrinogen, recruiting more platelets into a stable plug. Both these binding activities of VWF are the highest in the largest VWF multimers. Second, VWF is a specific carrier of factor VIII (FVIII) in plasma. VWF protects FVIII from proteolytic degradation, prolonging its half-life in circulation and efficiently

STA-9090 nmr localizing it at the site of vascular injury. Each monomer of VWF has one binding domain, located in the first 272 amino acids of the mature subunit (D’–D3 domain) able to bind one FVIII molecule. These functions are explored by an array of laboratory Selleck Temsirolimus assays, but no one reflects the whole spectrum of VWF activities. The deficiency or abnormal function of VWF causes von Willebrand’s disease (VWD), the most frequent inherited bleeding disorder [3]. VWD is heterogeneous because molecular defects can occur in more than one of the functional domains of the multimeric glycoprotein. As a consequence VWD is classified in three different types: partial quantitative deficiency (type 1), qualitative deficiency (type 2) and complete quantitative deficiency (type 3). Tests for the

correct diagnosis of VWD ideally have to explore the most important VWF properties: the antigenic level of VWF (VWF:Ag); the VWF–platelet GpIb interaction (VWF:RCo); the VWF–subendothelium–collagen interaction (VWF:CB); the VWF–FVIII interaction (VWF:FVIIIB) and the capacity of VWF to be organized into multimers.

Factor VIII procoagulant activity (FVIII:C) is also included in the diagnostic work-up, because it reflects the ability of VWF to protect it from degradation and is a useful complement in suspecting type 2N variants (see below). Table 1 summarizes the functional test for VWD diagnosis. With see more these tests, a useful classification in VWD types can be reached. The VWF:RCo explores the interaction of VWF with the platelet GpIb/IX/V complex and is still the standard method for measuring VWF activity. Abnormal VWF:RCo/VWF:Ag ratio (<0.6) usually indicates the presence of qualitative variants (type 2 VWD). Both aggregometric and turbidimetric methods appear useful. The aggregometric test however may be difficult to standardize and presents a low sensitivity at very low VWF concentrations (usually <10 U dL−1). Furthermore, careful calibration and standardization are essential [4]. In the recent years, the sensitivity of VWF:RCo has been significantly improved by using ELISA assays with recombinant GpIb [5,6]. The improved sensitivity of the ELISA VWF:RCo assay should enhance the reliability of the ratio determination, which however is difficult to obtain at very low VWF:Ag concentration.