Hemostasis Reference Laboratory

von Willebrand Activity by Ristocetin Cofactor

• Transaction Code: 3210-03
• CPT Code (Suggested): 85245

Ristocetin is a negatively charged antibiotic that induces platelet agglutination in vitro. Plasma vWF activity is determined by the ability of patient’s plasma to support ristocetin-induced agglutination of normal formalin-fixed platelets. Reduced levels are characteristic of von Willebrand disease, in which factor VIII levels are usually reduced proportionately. Falsely elevated values may occur with stress, inflammation, pregnancy, estrogen therapy, or exercise. Values are also affected by ABO blood type, with type O averaging 15-30% lower than non-O.

• Sample Required: 0.5 ml frozen plasma x4 or (2) 3.2% sodium citrated tubes, 5 ml each.
• See Sample Requirements when ordered with other tests.
• Normal Range: 37-154% effective 11/1/11
• Analytic Time: Run once weekly; depending upon requests, available STAT