Whole blood aggregation in von Willebrand disease

Platelet function testing in von Willebrand disease is generally performed in platelet rich plasma using an optical system. The characteristic abnormality is an abnormal response to the agglutinating agent, ristocetin. Platelet aggregation can be also studied in whole blood using either an impedance aggregometer or a particle counter. Fifteen patients with von Willebrand disease and fifteen normal subjects were studied using both whole blood methods. In the impedance system, normal subjects responded to ristocetin (1 mg/ml) with short lag phases (less than 70 sec) and normal maximum aggregation greater than 5 omega). Only three patients with von Willebrand disease responded with normal maximal aggregation but each of these had a prolonged lag phase, and this may be a useful diagnostic parameter. In the particle counter, discrimination between normals and some von Willebrand disease patients was possible but an overlap between normals and von Willebrand patients is evident. It is concluded that the platelets in patients with von Willebrand disease exhibit the same abnormalities in whole blood as in platelet rich plasma and that the combination of impedance aggregometry and a factor VIII procoagulant assay is a time-efficient and sensitive method to screen for von Willebrand disease.