Whole blood ristocetin‐induced platelet impedance aggregometry does not reflect clinical severity in patients with type 1 von Willebrand disease

Background The haemorrhagic phenotype in patients with von Willebrand disease (VWD) is heterogeneous, and assays of von Willebrand factor ristocetin cofactor activity (VWF:RCo) do not always reflect clinical severity, especially in those individuals classed as type 1 VWD. Recent studies have shown that whole blood ristocetin‐induced platelet agglutination (WB‐RIPA) using an easy‐to‐use analyzer, Multiplate® platelet impedance technique, could be informative as a diagnostic test in VWD, although inconsistencies were evident in patients with the type 1 disorder, possibly associated with clinical symptoms. Aim To investigate the relationship between WB‐RIPA, bleeding scores (BS) and VWF‐related measurements in type 1 VWD. Methods WB‐RIPA assay using the Multiplate® was performed using whole blood from 55 patients with type 1 VWD. BS was determined using a standardized questionnaire. Results WB‐RIPA values were significantly lower in type 1 VWD than in healthy controls ( P  < 0.0001). Weak correlations were apparent between WB‐RIPA and VWF:RCo or VWF antigen (VWF:Ag; r  = 0.22 or 0.28, respectively). There were significant differences in VWF:RCo ( P  = 0.036) and VWF:Ag ( P  = 0.0013) between patients with BS ≥4 (defined as abnormal bleeding tendency) and BS <4 (defined as no abnormal bleeding tendency), respectively. However, no significant difference was observed in WB‐RIPA between the BS ≥4 group and BS <4 group. Overall, VWD patients with a WB‐RIPA level >70 U did not seem to have an abnormal bleeding tendency, but low levels of WB‐RIPA did not correlate with BS. Conclusion WB‐RIPA did not reflect clinical severity in type 1 VWD patients.