Von Willebrand disease (VWD) is the most common inherited bleeding disorder and is classified into three major types. Types 1 and 3 VWD involve quantitative deficiencies in von Willebrand factor (VWF); these deficiencies are less severe in type 1 (the most common type, which includes the 1C subtype ) and more severe in type 3. Type 2 VWD involves qualitative abnormalities in VWF and includes subtypes 2A, 2B, 2M, and 2N. Acquired VWD (known as acquired von Willebrand syndrome [aVWS]) can also occur, although it is rare. A broad range of clinical bleeding is associated with VWD. Although no single laboratory test can be used to diagnose VWD, the initial panel of tests typically includes VWF antigen, VWF factor activity (such as ristocetin cofactor activity [VWF:RCo]), and factor VIII (FVIII) activity tests. These tests should be performed if VWD is suspected. Additional tests may be indicated for subtyping or genetic counseling.
Quick Answers for Clinicians
A workup for von Willebrand disease (VWD) initially involves evaluation of von Willebrand factor (VWF) quantity and function and factor VIII (FVIII) activity. Specific laboratory tests include VWF antigen, VWF ristocetin cofactor (VWF:RCo) activity (or another activity assay), and FVIII activity tests. The National Heart, Lung, and Blood Institute (NHLBI) and American Society of Hematology (ASH) guidelines designate levels of either VWF antigen or VWF:RCo <30 IU/dL (30% of normal) as diagnostic for VWD, regardless of bleeding, and a level of <50 IU/dL with abnormal bleeding as confirmatory for the diagnosis of VWD. Additional tests can be used to distinguish subtypes, and genetic testing may be used for diagnosis and subtyping of difficult cases, genetic counseling, or to assist with treatment decisions (see Laboratory Testing).
Von Willebrand factor (VWF) values fluctuate over time, mild disease can yield normal lab test results, and VWF levels that are only mildly decreased are not diagnostic for von Willebrand disease (VWD). VWF is an acute phase reactant, and VWF levels are affected by stress, recent exercise, illness, estrogen, inflammatory states, and some medications. For that reason, repeat testing on a new plasma sample collected at a different time may be necessary for conclusive results. In addition, blood type influences test results: Patients with blood type O have 25% lower VWF antigen concentrations than those with blood type A. VWF and factor VIII (FVIII) results can also be affected by pretest factors such as collection technique and specimen handling. (Refer to ARUP’s Special Specimen Collection and Handling guidelines for hemostasis/thrombosis specimens.)
Genetic testing is typically not part of the initial workup for von Willebrand disease (VWD), but can be useful for phenotype confirmation, to help distinguish subtypes with similar phenotypes, and in the evaluation of family members of individuals who have known variants. Genetic testing can differentiate between type 2B and platelet-type VWD, and type 2N VWD and hemophilia A. In patients diagnosed with type 1 VWD on the basis of clinical history and laboratory tests, genetic analysis is not indicated.
Von Willebrand disease (VWD) assays, specifically von Willebrand factor ristocetin cofactor (VWF:RCo) activity (or another activity assay) and factor VIII (FVIII) activity, are recommended for monitoring patients with VWD who are being treated with medications such as desmopressin or VWF concentrates. These tests are also recommended before surgery or during pregnancy in patients with VWD. See Monitoring.
Indications for Testing
- Diagnosis of VWD in individuals with a personal history and physical examination that suggest a mucocutaneous bleeding disorder, particularly those with epistaxis, bleeding of gums, menorrhagia, or excessive mucosal bleeding after surgery
- Diagnosis in individuals with a family history of VWD or mucocutaneous bleeding disorder
- Monitoring in patients with an established diagnosis of VWD who are undergoing treatment or have a planned surgery
Initial Hemostasis Tests
Initial tests in those with suspected bleeding disorders typically include CBC with platelet count, prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen, and thrombin time (TT). However, basic clotting times and CBC have limited use in the diagnosis of VWD because they are normal in most VWD subtypes.
Platelet function and aPTT tests are neither sensitive nor specific for VWD, but will give abnormal results in severe VWD and often normal results in mild/moderate VWD.
If the patient has no abnormalities detected by initial hemostasis tests or has an isolated prolonged aPTT result that corrects with a 1:1 mixing study, an initial VWD assay panel is indicated for further evaluation.
Initial Von Willebrand Disease Assays
If the patient has a significant history of mucocutaneous bleeding, VWD assays should be included as part of the initial workup. No single test is used for diagnosis; it is necessary to use the tests in combination.
A variety of factors, such as stress, recent exercise, estrogen treatment (or pregnancy), inflammatory conditions, illness, and some medications can affect VWD levels, so it may be necessary to repeat the tests on a new plasma sample collected at a different time for definitive results. These tests are available as panel tests; see ARUP Laboratory Tests below.
The Expected Laboratory Values in VWD by Type table describes typical results for these tests. If initial results are not diagnostic of VWD but there is high clinical suspicion for VWD, consider repeating tests in 1-3 months.
Von Willebrand Factor Antigen
VWF antigen levels usually range from 50-200 IU/dL (50-200% of normal). Levels <50 IU/dL are considered low and are diagnostic of VWD in a patient with abnormal bleeding, and levels <30 IU/dL (30% of normal) are considered diagnostic for VWD regardless of bleeding history. However, some patients with type 1 or 2 VWD may have levels in the range of 30-50 IU/dL ; these patients may also be asymptomatic or have minimal symptoms. In addition, patients with blood type O have 25% lower concentrations than those with blood type A.
Von Willebrand Factor (Ristocetin Cofactor) Activity
The VWF:RCo assay is used to measure how effectively the VWF in plasma is able to bind platelets when ristocetin is present. However, the VWF:RCo assay has some limitations because it can be influenced by sequence variations in the VWF gene, which can affect the ability of VWF to bind to ristocetin in the test while not interfering with VWF activity in vivo. In such cases, the test result can suggest VWD when the disease is not present (false-positive result). There are also other types of VWF activity tests that do not utilize ristocetin, such as collagen binding assays or glycoprotein 1b (GP1b) binding assays.
Von Willebrand Factor GPIbM Activity
The von Willebrand factor GPIbM activity (VWF:GPIbM) assay, or other newer activity assays, can be used as an alternative to VWF:RCo. Certain genetic variants (eg, p.D1472H) affect the ability of VWF to bind to ristocetin but do not affect VWF function. Unlike the VWF:RCo assay, the VWF:GPIbM assay does not use ristocetin and thus does not give false results due to these genetic variants. (This test has limited availability in the United States.) There are also other newer activity assays that continue to use ristocetin as a reagent.
Factor VIII Activity
An FVIII activity assay can be used to measure the activity levels of this factor in plasma. VWF is a carrier protein for FVIII, and individuals with type 1 or 2 VWD may have reduced levels of FVIII, whereas concentrations of FVIII in type 3 VWD are markedly reduced. FVIII levels may also be greatly decreased in type 2N VWD.
Von Willebrand Factor Activity/Antigen Ratio
The ratio of VWF activity (VWF:RCo or other activity) to VWF antigen can be used to detect a qualitative deficiency in VWF platelet binding (or collagen binding) ability and therefore can aid in distinguishing between type 1 and most cases of type 2 VWD, given that type 1 involves a quantitative and type 2 a qualitative deficiency. Type 1 VWD generally causes a decrease in both the VWF antigen and the VWF:RCo, so the ratio of the two would be approximately 1 in type 1 disease (the activity is low because the protein amount is low). In type 2 disease, VWF activity is more greatly affected than is VWF quantity due to decreased function, and the decreased ratio reflects that difference. A ratio of <0.7 is common in type 2 disease, although patients with type 2N disease often do not show a decreased ratio and instead have a discrepancy between VWF antigen and the FVIII level.
A desmopressin trial with postinfusion bloodwork after 1 hour and again after 4 hours should be performed when type 1C VWD is suspected. Type 1C VWD is a result of increased VWF clearance, which is caused by variants such as the VWF missense variant R1205H and can be detected by a desmopressin trial. A >30% decrease in VWF from peak concentrations, as identified by 4-hour postinfusion bloodwork, indicates an increased VWF clearance compatible with type 1C VWD. This testing should not be performed in individuals who cannot safely undergo the test (eg, very old or very young patients).
Analysis of VWF multimers using a qualitative assay is helpful in distinguishing type 1 and type 2 VWD and is therefore useful as a second-line test if type 2 VWD is suspected after antigen and activity testing have been performed. However, multimeric analysis can be a useful initial test if aVWS is suspected. The assay results indicate the presence and pattern of the different sizes of multimers. VWF multimers are considered normal if there is a full spectrum of sizes from large to small; the absence of high- and/or intermediate-molecular-weight multimers (large multimers) is an abnormal result. Types 2A, 2B, and platelet type (also called pseudo VWD) usually demonstrate abnormal multimeric distributions, whereas types 1, 2N, and 2M VWD are expected to show a normal pattern of multimers. Type 3 VWD shows a marked decrease in multimers of all sizes or a complete absence of multimers.
Ristocetin-Induced Platelet Aggregation
The low-dose ristocetin-induced platelet aggregation (RIPA) test, or low-dose RIPA, uses a lower dose of ristocetin than that used for the VWF:RCo test described above. Designed to detect the VWF hyperactivity associated with type 2B VWD and platelet-type VWD, it can be useful for subtype evaluation, particularly to distinguish type 2B and platelet-type VWD from other VWD types. However, genetic testing is typically preferred to diagnose patients with type 2B VWD. RIPA testing is less sensitive than the standard testing panel for detecting most subtypes of VWD.
RIPA testing must be performed by a local laboratory because of limited specimen stability.
Von Willebrand Factor-Platelet Binding
The VWF-platelet binding test is designed to detect the abnormally increased platelet binding seen in type 2B disease and helps to differentiate type 2B from platelet-type VWD. Ordering should be limited to specialists. (This testing is not performed at ARUP Laboratories.)
Von Willebrand Factor-Factor VIII Binding
The VWF-FVIII binding test measures the degree to which VWF can bind recombinant FVIII and can be used to characterize type 2N VWD (FVIII binding defects) and distinguish it from mild hemophilia A. Ordering should be limited to specialists. (This testing is not performed at ARUP Laboratories.)
Von Willebrand Factor-Collagen Binding
The VWF-collagen binding assay (VWF:CB) is sometimes used for VWD testing and is helpful for distinguishing type 1 VWD from type 2 VWD, similar to the way that VWF:RCo or other activity tests can be used for type differentiation. The VWF:CB/VWF antigen (VWF:Ag) ratio may also be useful to distinguish among VWD types 2A, 2B, and 2M. Ordering should be limited to specialists. (This testing is less commonly used in the United States and is not performed at ARUP Laboratories.)
Genetic testing is recommended for specific situations, such as for subtype confirmation when results might affect therapeutic decisions. Genetic testing is not widely available for types 1 and 3 VWD and is most useful for type 2 diagnosis.
Genetic/molecular testing can help distinguish subtype 2B from platelet-type VWD, and subtype 2N from hemophilia A, and can be useful in the evaluation of family members of individuals with known variants. Refer to the Von Willebrand Disease (VWF) Sequencing Test Fact Sheet for more information about specific variants associated with VWD types.
VWD assays are recommended for monitoring patients receiving medications such as desmopressin or VWF concentrates for VWD (appropriate treatment depends on subtype). VWF:RCo (or another activity assay) and FVIII activity tests are recommended at baseline and should be repeated within 1 hour of desmopressin administration to determine adequate response before use as a therapy. Repeat testing is suggested 2-4 hours after drug administration to assess the possibility of rapid clearance. VWF:RCo and FVIII activity tests are also indicated before surgery in patients with VWD to assess whether target activity levels have been achieved with prophylaxis.
ARUP Laboratory Tests
Electrophoresis/Clotting/Microlatex Particle-Mediated Immunoassay/Platelet Agglutination
Components: VWF multimers, VWF antigen, VWF:RCo, and FVIII activity
Quantitative Enzyme-Linked Immunosorbent Assay (ELISA)
Enzyme-Linked Immunosorbent Assay
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