Test Directory

von Willebrand Factor Activity, Plasma

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Updated Test Information:

Test Description
von Willebrand Factor Activity, Plasma

Ristocetin cofactor; VFW Activity; Von Willebrand factor activity

Test ID
General Information

Useful for:

  • Diagnosis of von Willebrand disease (VWD) and differentiation of VWD subtypes or differentiation of VWD from hemophilia A

  • Monitoring therapeutic efficacy of treatment with DDAVP (desmopressin) or VWF concentrates in patients with VWD

  • If von Willebrand factor activity is less than 55%, then the von Willebrand factor ristocetin cofactor activity assay will be performed at an additional charge

Specimen Type

Citrated Plasma

Specimen Requirements

Light-blue top (3.2% sodium citrate)

Specimen Collection / Processing Instructions

  • Specimen Type: Platelet-poor plasma

  • Collection Container/Tube: Light-blue top (3.2% sodium citrate)

  • Submission Container/Tube: Plastic vial (polypropylene preferred)

  • Specimen Volume: 2 mL in 2 vials each containing 1 mL

  • Collection Instructions:

    • Specimen must be collected prior to factor replacement therapy

    • Centrifuge, transfer all plasma into a polypropylene vial, and centrifuge plasma again

    • Aliquot plasma (1-2 mL per aliquot) into 2 separate polypropylene vials leaving 0.25 mL in the bottom of centrifuged vial

    • Freeze plasma immediately (no longer than 4 hours after collection) at -20 degrees C or, ideally, ≤ -40 degrees C

    • Send specimens in the same shipping container

  • Additional Information:


Frozen 14 days

Unacceptable Specimen Conditions

  • Gross hemolysis

  • Gross lipemia

  • Gross icterus


  • Measurement of von Willebrand factor (VWF) activity alone has limited diagnostic value. The diagnosis of von Willebrand disease (VWD) requires a combination of clinical and laboratory information. VWF activity assay results generally must be used together with assays of VWF antigen and factor VIII coagulant activity for optimum clinical utility and diagnostic efficiency

  • Results may be affected by:

    • Unfractionated heparin >4.0 U/mL; may cause an overestimation of the test result

    • Hemoglobin >70 mg/dL; may cause the result to be underestimated

    • Bilirubin >4.2 mg/dL; may cause the result to be underestimated

    • Triglycerides >1020 mg/dL; may cause the result to be underestimated

    • Rheumatoid factor >200 IU/mL; may cause an overestimation of the test result

  • Specimens from patients who have received preparation of mouse monoclonal antibody for diagnosis or therapy may contain human antimouse antibody (HAMA). The presence of HAMA may cause an overestimation of results in immunoassays that utilize mouse monoclonal antibodies. This assay contains a blocking agent against HAMA to minimize this interference.


Latex Immunoassay (LIA)

Estimated TAT

3-7 days

Testing Schedule



7 days

CPT Code(s)


Additional Information
Minimum Sample Volume

0.5 mL

Reference Range


Normal, full-term newborns may have mildly increased levels which reach adult levels by 90 days postnatal. Healthy, premature infants (30-36 weeks gestation) may have increased levels that reach adult levels by 180 days.

Individuals of blood group "O" may have lower plasma von Willebrand factor (VWF) activity than those of other ABO blood groups, such that apparently normal individuals of blood group "O" may have plasma VWF activity as low as 40% to 50%, whereas the lower limit of the reference range for individuals of other blood groups may be 60% to 70%.

Reflex Conditions

RIST: Ristocetin Cofactor

Performing Lab


LOINC Code(s)