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von Willebrand Factor Activity (Ristocetin Cofactor / GPIb Binding)

Measures how well von Willebrand factor helps platelets stick to a wound. It is one of the main tests used to look into von Willebrand disease.

AI-verified against cited sources. Awaiting expert reviewAlso called VWF:RCo, VWF:GPIbM, VWF:GPIbRLOINC 68324-3

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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 grabs platelets and helps them stick to the wound. It also carries factor VIII, another clotting protein, in the blood. This test measures how well VWF binds platelets, which is called its activity. Labs use ristocetin cofactor (RCo) tests or newer GPIb-binding tests, which aim at the same job. The result is a percent of normal, and it is usually ordered with VWF antigen and factor VIII.

Why it matters

Low VWF activity is the 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. Activity is also compared with antigen, because activity that is much lower than antigen can point to a type 2 form. The test is also used to follow treatment.

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 antigen 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 antigen 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 activity 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 Activity 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
  • The method: the older ristocetin cofactor test is less reproducible at low levels than newer GPIb-binding tests
  • 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.
  • Methods differ. The older ristocetin cofactor test is less reproducible at low levels than newer GPIb-binding tests, so the same blood can give different numbers by method.

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

  • Which method did my lab use, ristocetin cofactor or GPIb binding?
  • 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 antigen 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 activity 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 activity and VWF antigen?

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 Activity unit converter

Is a change real?

VWF Activity naturally varies about 17% from test to test in the same healthy person. Between two results from the same lab, a rise of 69% or more, or a fall of 41% 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 is a multimeric glycoprotein that carries factor VIII and tethers platelets to damaged vessel walls through glycoprotein Ib (GPIb). Activity assays measure this platelet-dependent function. The older ristocetin cofactor assay (VWF:RCo) measures ristocetin-induced agglutination of platelets. Newer assays use latex particles with recombinant GPIb, either with ristocetin (VWF:GPIbR) or with a gain-of-function GPIb that needs no ristocetin (VWF:GPIbM). They are easier to automate, and a 2023 review expects them to be more robust than RCo, which historically has high variability and poor sensitivity at low VWF levels. ARUP runs both RCo (platelet agglutination) and GPIbM (immunoturbidimetry) with the same adult interval of 51–215%. Mayo uses a latex immunoassay (55–200%) and adds an RCo assay when the activity is under 55%. The ASH/ISTH/NHF/WFH 2021 guideline treats VWF antigen and/or platelet-dependent activity (such as VWF:GPIbM) 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. 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.

LOINC 68324-3 (primary), 6014-5, 107372-5, 107378-2, 4680-5. Specimen: plasma.

Sources

  1. von Willebrand Factor Activity (Ristocetin Cofactor) (test 0030250), ARUP Laboratories
  2. von Willebrand Factor (VWF) GPIbM Activity (test 3019671), ARUP Laboratories
  3. von Willebrand Factor Activity, Plasma (test ID VWACT), Mayo Clinic Laboratories (Extended Catalog, via testcatalog.org)
  4. Thrombosis & Hemostasis Reference Ranges (updated 1/11/2021), Indiana University Health Pathology Laboratory (2021)
  5. von Willebrand Disease Profile, Plasma (test ID AVWPR), Mayo Clinic Laboratories (Extended Catalog, via testcatalog.org)
  6. Von Willebrand Factor Activity (test code VWFACT), UW Medicine, Department of Laboratory Medicine and Pathology
  7. ASH ISTH NHF WFH 2021 guidelines on the diagnosis of von Willebrand disease, Blood Advances (2021)
  8. 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)
  9. Relationship between ABO blood group and von Willebrand factor levels: from biology to clinical implications, Thrombosis Journal (2007)
  10. 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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