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Test Code VWF von Willebrand Factor Functional, Risto Cofactor (GPIb Binding) Activity

Specimen Type



Light blue top tube, 3.2% sodium citrate

Preferred Volume

2.7 mL

Offsite Collection Instructions

Whole blood sample must arrive in the laboratory within three hours of specimen collection.


If transport time exceeds three hours, follow centrifugation instructions:

  • Samples must be centrifuged at >1500 x g for 10 minutes at room temperature.
  • Carefully remove the plasma from the cells using a plastic transfer pipette avoiding the buffy coat.
  • Aliquot removed plasma into 2 plastic tubes containing a minimum of 500 uL of specimen in each tube.
  • The plasma samples must then be frozen at -20ºC.
  • Once solidly frozen, they must be shipped on dry ice. Samples that have thawed in transit will be rejected.

Note: For clients who do not have access to dry ice DO NOT freeze the specimen. Follow the centrifugation instructions and send fresh plasma or send whole blood sample. It now becomes vital that the specimen arrives in the lab within three hours of collection.

UCMC Collection Instructions

Specimens may be collected and sent to the laboratory at any time.

Test can be added on to an existing order up to 4 hours following the time of blood draw.


Sample may be collected 24/7. Test is performed Monday – Friday, 8:00 am – 2:00 pm

Turnaround Time

Monday-Friday 12 hours

STAT Availability

Not Available

Test Methodology


Additional Information

All 3.2% sodium citrate light blue top tubes require a ratio of 9 parts blood to 1 part anticoagulant (example: a 3.0 mL tube requires 2.7 mL blood added to 0.3 mL of anticoagulant).

CPT Code


Test Includes

vWF, Risto Cofactor (GPIb Binding) Activity

Reference Range

55-165%; range established 8/21/12

Minimum Volume

2.7 mL

Fee Code