Indications for Testing
Laboratory testing for VWD is appropriate in the following circumstances :
- 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
Laboratory Testing
Diagnosis
Initial Hemostasis Tests
Initial tests in those with suspected bleeding disorders typically include CBC with platelet count, prothrombin time (PT), and activated partial thromboplastin time (aPTT); fibrinogen or thrombin time (TT) tests can also be considered. 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, inflammatory conditions, illness, and some medications can affect VWD test results, 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 Lab Tests below.
The table below, Expected Laboratory Values in VWD by Type, describes typical results for these tests. If initial results are incompatible with VWD but there is high clinical suspicion for VWD, consider repeating tests in 1-3 months.
Von Willebrand Factor Antigen
The VWF antigen concentration, or amount of the protein present in the patient’s plasma, is generally determined using an immunoassay. VWF antigen levels usually range from 50-200 IU/dL. Levels <50 IU/dL are considered low, and levels <30 IU/dL (<20-30% of normal) are considered diagnostic for VWD. 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, as it can be influenced by sequence variations in the VWF gene, which can affect the ability of VWF to bind to ristocetin 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.
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, while 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 ability and therefore can aid in distinguishing between type 1 and most cases of type 2 VWD, since 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. In type 2 disease, VWF activity is more greatly affected than is VWF quantity, and the decreased ratio reflects that difference. A ratio of <0.6 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.
Second-Line Tests
Multimeric Analysis
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 after antigen and VWF:RCo testing have been performed. However, multimeric analysis may be a useful initial test if acquired VWD 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 is an abnormal result. Types 2A, 2B, and platelet type (also called pseudo VWD) demonstrate abnormal multimeric distributions, while types 1, 2N, and 2M VWD are expected to show a normal pattern of multimers. Type 3 VWD shows a marked decrease in multimers 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. Additional testing, such as genetic testing, is usually necessary to distinguish type 2B from platelet-type 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. (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 and distinguish it from mild hemophilia A, in which there are FVIII binding defects. (This testing is not performed at ARUP Laboratories.)
Von Willebrand Factor-Collagen Binding
The VWF-collagen binding assay is sometimes used for VWD testing and is helpful for distinguishing type 1 VWD from types 2A, 2B, and 2M, similar to VWF:RCo or other activity tests. Ordering should be limited to specialists. (This testing is less commonly used in the United States.)
Genetic Tests
Genetic testing is recommended primarily for specific situations, such as for subtype confirmation when results might affect therapeutic decisions. Molecular 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 Additional Technical Information document, von Willebrand Disease Genetic Subtyping – Type 2 and Platelet Type, for more information about specific mutations associated with VWD types.
Expected Laboratory Values in VWD by Type
| VWD Type/Subtype |
|---|
| Lab Test |
1 |
2A |
2B and Platelet Type |
2M |
2N |
3 |
|---|
| VWF Ag (IU/dL) |
<30a |
<30-200 (commonly <50) |
<30-200 (commonly <50) |
<30-200 (commonly <50) |
30-200 |
Absent |
| VWF:RCo (IU/dL) |
<30a |
<30a |
<30a |
<30a |
30-200 |
Absent |
| FVIII |
Low or normal |
Low or normal |
Low or normal |
Low or normal |
Mildly to markedly low |
Severely low (<10 IU/dL) |
| RCo:VWF Ag ratio |
>0.5-0.7 |
<0.5-0.7 |
Typically <0.5-0.7 |
<0.5-0.7 |
>0.5-0.7 |
n/a |
| Multimer pattern |
Normal pattern but reduced intensity |
Abnormal; loss of HMW and IMW multimers |
Abnormal; loss of HMW multimers |
Normal pattern, may have reduced intensity |
Normal |
No VWF present |
| RIPAb |
Usually normal |
Often reduced aggregation at high ristocetin concentrations but no enhanced aggregation at low ristocetin concentrations |
Abnormal; enhanced aggregation at low ristocetin concentrations |
Reduced at high ristocetin concentrations |
Normal |
Absent |
| VWF:FVIII binding |
Normal |
Normal |
Normal |
Normal |
Low |
n/a |
| aThe NHLBI designates levels of either VWF antigen or VWF:RCo <30 IU/dL as diagnostic for VWD; however, some patients with subtype 1 or 2 will have values of 30-50 IU/dL
bRIPA must be performed by a local laboratory due to limited stability of specimen.
Ag, antigen; HMW, high molecular weight; IMW, intermediate molecular weight; n/a, not applicable; NHLBI, National Heart, Lung and Blood Institute
Sources: NHLBI, 2008 ; Favaloro, 2014
|
Monitoring
VWD assays are recommended for monitoring patients receiving medications such as desmopressin or VWF concentrates for VWD (appropriate treatment depends on subtype). VWF:RCo and FVIII activity tests are recommended at baseline and should be repeated within 1 hour of desmopressin administration to determine adequate response prior to 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.
