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Ristocetin Cofactor

This test evaluates the function of von Willebrand factor by testing ristocetin-induced aggregation of normal platelets in the presence of the patient’s plasma. It measures the binding activity of vWF to platelet glycoprotein 1b. RcoF is the most sensitive and specific test for von Willebrand’s disease, and is decreased in virtually all types of the disease.

Levels may be increased in liver disease, pregnancy, estrogen therapy, and after exercise. Levels in the same individual may be quite variable from time to time. Levels vary with blood group; normal individuals with blood group O may have levels below the reference range. In patients with mild von Willebrand disease, ristocetin cofactor activity may at times be in the low normal range. If the diagnosis is strongly suspected, testing should be repeated within weeks or months.

Reference range is 50 - 200%.

Specimen requirement is one light blue top (sodium citrate) tube of blood.

See von Willebrand’s Disease Screening Panel.

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