Diagnosis of von Willebrand Disease

Clinical Evaluation

• The American Society of Hematology recommends using a validated bleeding assessment tool to systematically evaluate bleeding symptoms, as 80% of specialists rely on these instruments to guide testing decisions, with a focus on mucocutaneous bleeding patterns, such as epistaxis, menorrhagia, and easy bruising 1, 2, 3
• A strong family history of bleeding disorders or similar symptoms is a key factor in diagnosing von Willebrand disease, particularly in patients with a history of bleeding after surgical or invasive procedures 2
• Physical examination findings, including ecchymoses, hematomas, petechiae, or active bleeding sites, can indicate von Willebrand disease, and should be considered in conjunction with laboratory test results 4

Laboratory Testing

• The National Heart, Lung, and Blood Institute (NHLBI) guidelines recommend initial laboratory testing, including complete blood count (CBC) with platelet count and peripheral smear, prothrombin time (PT), and activated partial thromboplastin time (aPTT), to rule out other bleeding disorders 1, 4
• Mandatory initial VWD assays, including VWF antigen (VWF:Ag), VWF ristocetin cofactor activity (VWF:RCo), and Factor VIII coagulant activity (FVIII), should be ordered simultaneously for patients with strong mucocutaneous bleeding history, with normal reference ranges of 50-200 IU/dL for all three tests 1, 4
• Critical pre-analytical considerations, including atraumatic blood draw, minimizing patient stress, avoiding testing during acute illness or pregnancy, and proper sample handling, are essential for accurate test results 1, 2, 3

Interpretation of Test Results

• Diagnostic thresholds, including VWF:RCo <30 IU/dL for definitive diagnosis of VWD, and VWF:RCo 30-50 IU/dL with supportive clinical/family history for likely VWD, should be considered in conjunction with clinical evaluation and other laboratory test results 1, 4
• The VWF:RCo/VWF:Ag ratio <0.5-0.7 suggests Type 2 (qualitative) VWD rather than Type 1 (quantitative deficiency), and may require additional specialized testing, such as VWF multimer analysis or genetic sequencing of the VWF gene 1, 4

Specialized Testing

• VWF multimer analysis is not for initial screening, but rather for subtyping, and should be performed in specialized laboratories with expertise, to distinguish Type 2A, 2B, and 2M subtypes 4
• Additional specialized assays, including VWF collagen binding (VWF:CB), ristocetin-induced platelet aggregation (RIPA), and FVIII binding assay, may be necessary to confirm diagnosis and guide treatment selection 1, 4

Referral to Hemostasis Specialist

• Immediate referral to a hemostasis specialist is indicated for abnormal initial VWD assay results requiring subtyping, strong bleeding history with repeatedly normal tests, suspected acquired von Willebrand syndrome (AVWS), and guidance on repeat testing interpretation or access to specialized assays 1, 2, 3, 4

Diagnosis of von Willebrand Disease

Initial Laboratory Evaluation

• The American College of Hematology recommends that the diagnosis of von Willebrand disease requires three essential initial blood tests: VWF antigen (VWF:Ag), VWF ristocetin cofactor activity (VWF:RCo), and factor VIII coagulant activity (FVIII) 5, 6
• Complete blood count (CBC), prothrombin time (PT), and activated partial thromboplastin time (PTT) should be ordered if a bleeding disorder is suspected, though these do not specifically diagnose VWD 6, 7
• VWF antigen (VWF:Ag) measures the quantity of VWF protein, VWF ristocetin cofactor activity (VWF:RCo) measures VWF function, and factor VIII coagulant activity (FVIII) measures FVIII levels which are often affected in VWD 5, 8

Interpretation of Initial Tests

• A VWF:RCo/VWF:Ag ratio below 0.5-0.7 suggests qualitative VWD (Type 2) rather than quantitative deficiency (Type 1) 9
• Normal ranges for these tests are typically 50-200 IU/dL for VWF:Ag, VWF:RCo, and FVIII 9, 10
• A definitive diagnosis of VWD is typically made when VWF:RCo is <30 IU/dL 10

Specialized Testing

• VWF multimer analysis should be performed if initial testing reveals abnormal results or if clinical suspicion remains high despite normal initial tests 5, 8

Important Considerations for Testing

• Blood samples for VWF assays must be transported to the laboratory at room temperature, plasma should be separated from blood cells promptly at room temperature, and if testing will be delayed beyond 2 hours, samples must be frozen at or below -40°C 10
• Patient factors that can elevate VWF and FVIII levels include stress, recent exercise, inflammatory illness, pregnancy, and oral contraceptives 11
• The VWF:RCo assay has high coefficient of variation (10-30%), which may affect result interpretation 9, 10
• Repeat testing may be necessary due to variability in test results 10, 11
• Relying solely on a single test can lead to misdiagnosis - all three initial tests are required 11
• Failure to consider ABO blood type when interpreting results (type O is associated with lower VWF levels) 10
• Improper sample handling can significantly affect test results, potentially leading to false negatives or positives 10, 11
• Patients with VWF:RCo between 30-50 IU/dL may still have VWD if there is supporting clinical or family evidence 10

Diagnosis and Management of von Willebrand Disease

Clinical and Laboratory Assessment

• The American Heart Association recommends considering acquired von Willebrand syndrome (AVWS) in patients with aortic stenosis, lymphoproliferative disorders, or monoclonal gammopathies 12

Specialized Testing and Referral

• The American College of Cardiology suggests referral to a hemostasis specialist for VWF multimer analysis if the VWF:RCo/VWF:Ag ratio is <0.7 or clinical suspicion remains high despite borderline results, with a coefficient of variation of 10-30% for the VWF:RCo assay 12

Updated von Willebrand Factor Activity Assays

Automated Alternatives to the VWF:RCo Reference Test

• The traditional VWF ristocetin cofactor (VWF:RCo) assay continues to serve as the reference standard for measuring VWF functional activity, although newer automated assays are increasingly used for greater accuracy. 13
• VWF:GPIbR – an automated assay that uses recombinant wild‑type GPIb fragments combined with ristocetin; it provides improved analytical precision and a lower limit of detection (≈ 1–10 IU/dL) compared with VWF:RCo. 13
• VWF:GPIbM – an automated assay employing gain‑of‑function mutant GPIb fragments that bind VWF spontaneously without ristocetin, thereby removing false‑positive results that can occur with certain patient groups. 13
• VWF:Ab – an assay measuring the interaction between the VWF A1 domain and monoclonal antibodies; it cannot replace VWF:RCo because it misses some type 2M mutations (e.g., p.G1324A) and shows limited sensitivity for loss of high‑molecular‑weight multimers. 13

Laboratory Evaluation and Referral Recommendations for von Willebrand Disease

Initial Hemostasis Panel

• A complete blood count with platelet count should be obtained to detect thrombocytopenia, which can be isolated in qualitative Type 2B von Willebrand disease. 14
• Prothrombin time (PT) is recommended as a screening test for defects of the extrinsic coagulation pathway. 14
• Activated partial thromboplastin time (aPTT) may be prolonged when factor VIII levels are markedly reduced, but it is often normal in mild von Willebrand disease. 14
• Fibrinogen measurement or thrombin time can be performed optionally to exclude primary fibrinogen disorders. 14

Specialized Reflex Testing (ordered only after abnormal core results)

• Von Willebrand factor multimer analysis should be reserved for cases with abnormal initial assays or persistent high clinical suspicion, as it is not part of the initial screening. 15
• Multimer analysis differentiates Type 2A, 2B, and 2M subtypes by evaluating the electrophoretic pattern of von Willebrand multimers. 15
• Platelet‑derived von Willebrand factor studies measure the amount of von Willebrand factor stored in platelets and are useful in selected diagnostic algorithms. 15
• Individuals with blood group O have approximately 25 % lower baseline von Willebrand factor levels compared with non‑O groups, influencing interpretation of quantitative results. 15

Pre‑Analytical Considerations

• Testing should be avoided during acute illness, pregnancy, systemic inflammation, or within 48 hours after strenuous exercise because these conditions can falsely elevate von Willebrand factor levels. (Guideline recommendation) 15
• Stress during venipuncture can increase von Willebrand factor; therefore, minimizing patient anxiety is advised. (Guideline recommendation) 15

Pitfalls and Test Interpretation

• Bleeding time and PFA‑100 are not recommended as screening tools for von Willebrand disease due to inconsistent sensitivity and specificity. 15
• Ordering von Willebrand factor multimer analysis as an upfront test is discouraged because it is complex, costly, and should follow abnormal initial assay results. 15

Referral to a Hemostasis Specialist

• Refer patients when initial von Willebrand disease assays reveal abnormalities that require subtyping (e.g., atypical ratios or multimer patterns). 14
• Refer patients with a strong bleeding history despite repeatedly normal laboratory results; repeat testing or specialist evaluation is warranted. 14
• Referral is indicated for individuals whose von Willebrand factor ristocetin cofactor activity (VWF:RCo) falls between 30–50 IU/dL when supported by clinical or family history. 14
• Suspect acquired von Willebrand syndrome in the context of conditions such as aortic stenosis, lymphoproliferative disorders, or monoclonal gammopathies, and refer for specialized assessment. 14
• When specialized assays (e.g., multimer analysis, genetic sequencing) are needed for definitive diagnosis, a hemostasis specialist should be consulted. 14