Ristocetin Cofactor

*Take to processing ASAP.
CENTRIFUGE AND FREEZE PLASMA IMMEDIATELY

4459

LAB335
FACTOR 8
VON WILLEBRAND
CON VILLEBRAND ASSAY
F8 COFACTOR

1 mL frozen platelet-poor plasma collected in a 3.2% sodium citrate (light blue-top) tube

0.5 mL

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/mcL). Freeze immediately and ship on dry ice.

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 tube

Frozen

Room temperature: Unacceptable
Refrigerated: Unacceptable
Frozen: 30 days

Hemolysis • Lipemia • Thawed plasma received room temperature or refrigerated

Mon-fri

2-5 days

42-200 % normal

von Willebrand disease is the most common hereditary bleeding disorder. von Willebrand Factor is necessary for platelet adhesion to injured endothelium. Ristocetin cofactor is useful in assessing binding of von Willebrand Factor to platelet factor GP1b. When combined with other tests, results are useful in categorizing the type of von Willebrand disease.