VWF Activity by Ristocetin Cofactor

Profile or Test Panel
If the APTT is  prolonged and the factor VIII is normal, this panel reflexes to an APTT Reflexive Evaluation Profile. 
Indications Requires VW Antigen and FVIII levels to interpret results
Method Turbidometric
Test Information 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. Elevated values may occur with stress, inflammation, pregnancy, estrogen therapy, or exercise. 
Additional Test Information Normal Range:  37-154% effective 11/1/11
Sample Requirements Whole Blood:  3.2% Sodium Citrated (blue top)  OR
Frozen Plasma
Requested Volume Two 5 ml 3.2 sodium citrated (blue top) tubes as whole blood  OR
Frozen plasma in 4 X 1mL aliquots in plastic tubes 
Sample Information Whole blood is preferred for testing but if it is not possible to send whole blood tubes TO ARRIVE HERE WITHIN 3 HOURS of collection then send frozen plasma. To prepare plasma centrifuge blue top tubes at 1500g for 15 minutes and remove the plasma and centrifuge a second time at 1500g for an additional 15 minutes.  Aliquot approximately 1 ml of plasma into 4 plastic tubes, and freeze.  
Shipping Information Whole Blood:  Send at amibient temperature (18-25C) and must be received within the lab in less than or equal to 3 hours after collection.
Frozen Plasma:  send on dry ice 

Send samples to:

Bloodworks Northwest
Attn: Hemostasis Laboratory
921 Terry Ave
Seattle, WA 98104

For additional information, please see Ordering Information
Requisition Form RFT- Hemostasis Reference Laboratory
Transaction Code 3210-03
CPT Codes 85245
Turn around Time (analytic time) Run once weekly; depending upon requests, available STAT.
Report/ Results Fax number required to receive report