von Willebrand factor antigen (vWF:Ag)

What it measures

Measures the amount of von Willebrand factor, the protein that helps platelets stick to damaged vessels and carries factor VIII. Used with activity assays to diagnose von Willebrand disease.

Specimen and preparation

• Specimen: Citrated plasma (3.2% sodium citrate)
• Tube: Light_blue top
• Preparation: Avoid testing during acute illness, pregnancy or estrogen use, which raise levels. Do not chill whole blood.

Reference range

Reference ranges differ between laboratories, methods and populations. Always use the range printed on your own lab report.

Causes of high values

• Inflammation, stress, exercise
• Pregnancy, estrogen
• Vascular endothelial injury
• Liver disease

Causes of low values

• von Willebrand disease type 1 and 3
• Type 2 (activity lower than antigen)
• Acquired von Willebrand syndrome
• Hypothyroidism
• Blood group O (mildly lower)

Method

Latex immunoturbidimetric assay or ELISA

Good to know

Interpret with vWF activity (GP1bM or ristocetin cofactor) and factor VIII. An activity/antigen ratio below 0.7 suggests type 2 disease.

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