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von Willebrand Factor Antigen (VWF:Ag)

Measures how much von Willebrand factor is in your blood. It is usually ordered with VWF activity and factor VIII to look into von Willebrand disease.

AI-verified against cited sources. Awaiting expert reviewAlso called VWF:Ag, vWF Ag, VWF AgLOINC 27816-8

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What it is

Von Willebrand factor (VWF) is a large protein made by the cells that line your blood vessels and by platelets. When you are cut, it helps platelets stick to the wound. It also carries factor VIII, another clotting protein, in the blood. This test counts how much VWF protein is present, which is called the antigen level, and does not measure how well it works. The result is a percent of normal. Labs usually report it next to VWF activity and factor VIII.

Why it matters

A low VWF antigen level is a main lab sign of von Willebrand disease (VWD), the most common inherited bleeding disorder. Some people whose levels fall below the range never have a bleeding problem, and low levels are common in people with blood group O. The 2021 ASH/ISTH/NHF/WFH guideline uses a VWF level under 30 IU/dL, or under 50 IU/dL together with unusual bleeding, to confirm type 1 VWD. Comparing antigen with activity helps tell the types of VWD apart: when both are low in step, it is more typical of type 1, and when activity is much lower than antigen, it can point to a type 2 form.

If it’s low

A low value can be a sign of von Willebrand disease, but it can also be a normal variation. People with blood group O often have lower VWF, and some healthy people fall just below any lab range. A single low result is usually repeated, because levels change with stress, illness and pregnancy. Your clinician reads it with your bleeding history, VWF activity and factor VIII. The 2021 ASH/ISTH/NHF/WFH guideline uses a level under 30 IU/dL to confirm type 1 VWD whether or not you bleed, and a level under 50 IU/dL only if you also have unusual bleeding.

Common causes

  • Blood group O, which runs lower and is common
  • Natural variation, since some healthy people fall below the lab range
  • Inherited von Willebrand disease
  • Acquired von Willebrand syndrome, which is uncommon and happens alongside other health conditions

What can help

  • Ask whether the test should be repeated when you are well
  • Ask whether VWF activity and factor VIII were measured too, and what they show
  • If von Willebrand disease is confirmed, ask your care team for a plan for surgery, dental work, injuries and heavy periods

If it’s high

VWF antigen above the range is usually temporary. VWF rises with stress, pregnancy, infection, injury or surgery, and it tends to be higher with age and in people who do not have blood group O. A high value is not a diagnosis. If the test was done during an illness or injury, your clinician may repeat it when you are well.

Common causes

  • Stress, including hard exercise
  • Pregnancy
  • Infection, inflammation, injury or surgery (VWF is an acute-phase protein)
  • Older age
  • Blood groups A, B and AB, which run higher than group O

What can help

  • Usually nothing needs to be done
  • Ask your clinician whether the test should be repeated when you are well, because VWF changes with stress and illness

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

The usual range depends on age. Choose an age to see the one that applies.

Children and teens 6 ranges

See VWF Antigen by age and sex, with the U.S. survey numbers where they exist.

ASH/ISTH/NHF/WFH 2021 VWF level thresholds for confirming type 1 VWD (VWF antigen and/or platelet-dependent VWF activity; the guideline says to use the lab's own lower limit if it is below 50)

  • Under 30: supports a type 1 VWD diagnosis whether or not there is bleedingbelow 30 %
  • 30 to under 50: supports a type 1 VWD diagnosis only when there is unusual bleeding30 to under 50 %
  • 50 and above: above the guideline's type 1 thresholds (this does not rule out other types)50 and above %

What can affect your result

  • Blood group: group O runs lower than other groups
  • Stress, hard exercise, illness, injury and pregnancy raise VWF
  • Age: levels tend to rise with age
  • A recent blood transfusion or factor replacement
  • Sample handling: platelet-poor plasma that is frozen promptly
  • Blood group O gives lower VWF than other blood groups, so a result near the bottom of the range can be a normal variation.
  • VWF is an acute-phase protein. Stress, hard exercise, injury, surgery, infection and pregnancy can push it up, so the guideline asks for testing at baseline health.
  • A recent blood transfusion or factor replacement can change the result. Mayo asks that the sample be collected before factor replacement and, after a transfusion, not within 48 hours.
  • The sample must be platelet-poor plasma that was spun twice and frozen promptly. Platelets left in the sample can give spurious results.

VWF moves with stress, illness and pregnancy. The underlying inherited level stays about the same.

When to talk to a clinician

A low result is not an emergency by itself, but ask the clinician who ordered it to review it with you. Contact your clinician about heavy or long-lasting bleeding, such as nosebleeds that are hard to stop, very heavy periods, easy bruising, or bleeding after dental work or surgery. Call 911 or your local emergency number for bleeding that will not stop with firm pressure, a head injury, vomiting blood, or black stools.

Questions you could ask

  • How do my antigen and activity results compare with each other?
  • Was I ill, stressed or pregnant when this was drawn, and should we repeat it?
  • Should this test be repeated when I am well?
  • Were VWF activity and factor VIII measured too, and what do they show?
  • Does my blood type affect how this result should be read?
  • What should I know about bleeding risk before surgery or dental work?

Questions people ask

Does my blood type change my result?

Yes. People with blood group O often have lower VWF. Mayo notes that apparently healthy people in group O can have antigen as low as 40% to 50%, while the lower limit for other blood groups may be 60% to 70%. The 2021 guideline does not require blood-group-specific ranges, so your clinician will read your result with your bleeding history.

What is the difference between VWF antigen and VWF activity?

Antigen counts how much VWF protein is in your blood. Activity measures how well it works at helping platelets stick. Comparing the two helps your clinician tell the types of von Willebrand disease apart, and labs usually run both with factor VIII.

Can one result in the usual range rule out von Willebrand disease?

Not always. VWF levels change with stress, illness and pregnancy, so a borderline or unexpected result is often repeated when you are well. Your clinician decides what testing makes sense for you.

Show the science and sources

Units

  • 1 % = 1 %
  • 1 % = 1 IU/dL
  • 1 % = 0.01 IU/mL

Open the VWF Antigen unit converter

Is a change real?

VWF Antigen naturally varies about 12.7% from test to test in the same healthy person. Between two results from the same lab, a change of roughly 39% or more is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: Systematic review and meta-analysis of within-subject and between-subject biological variation data of coagulation and fibrinolytic measurands (Hollestelle MJ et al.).

For clinicians and researchers

VWF antigen is measured with an immunoassay, usually a latex-enhanced (microlatex or LIA) automated assay at ARUP and Mayo, and it quantifies VWF protein regardless of function. VWF is a multimeric glycoprotein that carries factor VIII and tethers platelets to damaged vessel walls through glycoprotein Ib. The ASH/ISTH/NHF/WFH 2021 guideline treats VWF antigen and/or platelet-dependent activity as the VWF level, confirms type 1 VWD at under 0.30 IU/mL regardless of bleeding or under 0.50 IU/mL with unusual bleeding (using the lab's own lower limit when it is below 0.50), says ABO-specific reference ranges are not required, and suggests an activity-to-antigen ratio under 0.7, rather than 0.5, to confirm type 2 VWD. A low antigen with a similar low activity fits type 1 or type 3 patterns, and a disproportionately low activity fits type 2. VWF is an acute-phase reactant, so testing belongs at baseline health. In a classic study of 1,117 healthy people, mean VWF antigen was 75 IU/dL in group O and 123 IU/dL in group AB, and the group O range extended below 50 IU/dL. Mayo's profile adds an RCo assay when VWF activity is under 55% and a multimer analysis when antigen or activity is under 40%.

LOINC 27816-8 (primary), 6012-9, 41867-3. Specimen: plasma.

Sources

  1. von Willebrand Factor Antigen (test 0030285), ARUP Laboratories
  2. Thrombosis & Hemostasis Reference Ranges (updated 1/11/2021), Indiana University Health Pathology Laboratory (2021)
  3. von Willebrand Disease Profile, Plasma (test ID AVWPR), Mayo Clinic Laboratories (Extended Catalog, via testcatalog.org)
  4. Von Willebrand Factor Antigen (test code VWFAG), UW Medicine, Department of Laboratory Medicine and Pathology
  5. ASH ISTH NHF WFH 2021 guidelines on the diagnosis of von Willebrand disease, Blood Advances (2021)
  6. Laboratory diagnosis of von Willebrand disease in the age of the new guidelines: considerations based on geography and resources, Research and Practice in Thrombosis and Haemostasis (2023)
  7. Relationship between ABO blood group and von Willebrand factor levels: from biology to clinical implications, Thrombosis Journal (2007)
  8. Influences of ABO blood group, age and gender on plasma coagulation factor VIII, fibrinogen, von Willebrand factor and ADAMTS13 levels in a Chinese population, PeerJ (2017)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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