Which laboratory finding is typical of von Willebrand disease?

Which laboratory finding is typical of von Willebrand disease?

• A. Prolonged bleeding time
• B. Decreased ristocetin cofactor activity
• C. Thrombocytopenia
• D. Prolonged PT

Answer: (B)

von Willebrand disease causes defective platelet adhesion because the von Willebrand factor that normally links platelets to the damaged endothelium is deficient or dysfunctional. A key lab test that reflects this defect is the ristocetin cofactor activity assay, which measures vWF’s ability to mediate ristocetin-induced platelet aggregation. When vWF is deficient or not functioning, this aggregation is impaired, so ristocetin cofactor activity is decreased—making this finding characteristic of the disorder. Other common labs can be normal or nonspecific: bleeding time may be prolonged due to impaired adhesion, but it’s not a precise test; PT is typically normal because the coagulation cascade is not primarily affected; thrombocytopenia is not a typical feature. Thus, decreased ristocetin cofactor activity best identifies von Willebrand disease.

von Willebrand disease causes defective platelet adhesion because the von Willebrand factor that normally links platelets to the damaged endothelium is deficient or dysfunctional. A key lab test that reflects this defect is the ristocetin cofactor activity assay, which measures vWF’s ability to mediate ristocetin-induced platelet aggregation. When vWF is deficient or not functioning, this aggregation is impaired, so ristocetin cofactor activity is decreased—making this finding characteristic of the disorder. Other common labs can be normal or nonspecific: bleeding time may be prolonged due to impaired adhesion, but it’s not a precise test; PT is typically normal because the coagulation cascade is not primarily affected; thrombocytopenia is not a typical feature. Thus, decreased ristocetin cofactor activity best identifies von Willebrand disease.