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von Willebrand Factor GPIbM Activity
Test Code13995
CPT Codes
85397
Preferred Specimen
1 mL frozen platelet-poor plasma collected in a 3.2% sodium citrate (light blue-top) tube
Minimum Volume
0.5 mL
Instructions
Platelet-poor plasma: Centrifuge light blue-top tube for 15 minutes at approximately 1500 g within 60 minutes of collection. Using a plastic pipette, remove plasma, taking care to avoid the WBC/platelet buffy layer and place into a plastic vial. Centrifuge a second time and transfer platelet-poor plasma into a new plastic vial. Plasma must be free of platelets (<10,000/uL). Freeze immediately and ship on dry ice. Alternative methods for preparation of platelet-poor plasma may be used if validated by the laboratory.
Note: Storage of whole blood at refrigerated temperatures prior to processing may lead to cryoprecipitate formation and falsely low Factor VIII and von Willebrand Factor studies.
Note: Storage of whole blood at refrigerated temperatures prior to processing may lead to cryoprecipitate formation and falsely low Factor VIII and von Willebrand Factor studies.
Transport Temperature
Frozen
Specimen Stability
Room temperature: Unacceptable
Refrigerated: Unacceptable
Frozen: 90 days
Refrigerated: Unacceptable
Frozen: 90 days
Methodology
Latex-based Turbidimetric
Setup Schedule
Set up: Tue, Thu, Sat; Report available: 2-5 days
Clinical Significance
Von Willebrand disease (VWD) is the most frequent inherited bleeding disorder and is characterized by either a quantitative or qualitative defect of von Willebrand Factor (VWF). During primary hemostasis, VWF mediates platelet adhesion and aggregation via binding to the platelet glycoprotein Ib (GPIB) receptor at the site of injury. VWF is also the specific carrier protein of Factor VIII, protecting FVIII from proteolytic degradation in circulation. The initial screening evaluation of VWD includes testing for VWF antigen, VWF activity, and Factor VIII activity. Historically, the most commonly performed VWF activity assay has been the Ristocetin Cofactor assay (VWF:RCo). The GPIbM activity assay is a ristocetin independent activity assay and provides several advantages over the VWF:RCo assay - improved sensitivity (eg. lower reporting limit) and precision, and insensitivity to benign VWF variants (seen in 60-70% and 15-20% of African and Caucasian descent, respectively) that reduce ristocetin interaction and potentially leading to a potentially false diagnosis of VWD or type 2 VWD (VWD associated with markedly decreased VWF activity compared to VWF antigen level). It should be noted that reference intervals are from non-ABO typed donors.
