Laboratory Diagnosis of Von Willebrand Disease

Standard Diagnostic Panel

• The essential laboratory work‑up for suspected von Willebrand disease (VWD) includes measurement of von Willebrand factor antigen (VWF:Ag), platelet‑dependent VWF activity using the newer VWF:GPIbM or VWF:GPIbR assays (preferred over the traditional VWF:RCo), and factor VIII coagulant activity (FVIII:C) [1][2].

Initial Screening Tests – Limited Utility

• Routine hemostasis screening (complete blood count, prothrombin time, activated partial thromboplastin time) is usually normal in VWD and therefore has limited diagnostic value [2][3].
• The platelet‑function analyzer (PFA‑100/200) is more sensitive than bleeding time for severe VWD but lacks sensitivity for mild disease and is not recommended for routine screening [2][3]4.
• Bleeding time is largely discontinued because of its invasiveness, poor reproducibility, and low sensitivity for VWD [2][3].
• When all screening tests are normal but clinical suspicion remains, specific VWF assays must still be performed [1][2].

Preferred Platelet‑Dependent VWF Activity Assays

• VWF:GPIbM (recombinant mutated GPIb, no ristocetin) and VWF:GPIbR (recombinant GPIb with ristocetin) are the recommended assays for platelet‑dependent VWF activity [1][5].
• These assays overcome the limitations of VWF:RCo, which suffers from poor reproducibility, high coefficient of variation, low sensitivity at very low VWF levels, and false‑low results in individuals of African ancestry carrying the D1472H variant [1][2].
• Current guidelines explicitly endorse the use of VWF:GPIbM or VWF:GPIbR over VWF:RCo for VWD evaluation [1][5].

Diagnostic Interpretation by VWD Type

• Type 1 VWD – Both VWF:Ag and VWF activity are reduced proportionally; FVIII:C may be normal or mildly decreased [5][6].
• Type 2 VWD – The ratio of VWF activity to VWF:Ag is < 0.7 (guideline cutoff, updated from the previous 0.5–0.7 range) [5][6]7.
• Type 3 VWD – VWF:Ag and VWF activity are < 0.05 IU/mL, and FVIII:C is < 0.10 IU/mL 8.

Specialized Assays

VWF Multimer Analysis

• Visualizes the distribution of plasma VWF multimers and is essential for distinguishing type 2A from type 2B and other type 2 variants [1][3].
• Not recommended for initial screening; performed only when core assays are abnormal or clinical suspicion is high [7][4].
• The technique is technically complex and yields qualitative results [7][4].

Ristocetin‑Induced Platelet Agglutination (RIPA)

• Differentiates type 2A from type 2B VWD [1][5]3.
• Requires a fresh blood sample, lacks standardization, and is unavailable in many laboratories [1][5].
• Guidelines now favor targeted genetic testing over RIPA for confirming type 2B VWD 8.

VWF:FVIII Binding Assay (VWF:FVIIIB)

• Assesses the ability of VWF to bind factor VIII and is essential for distinguishing type 2N VWD from mild hemophilia A [1][5]3.
• Either VWF:FVIIIB or targeted genetic testing is recommended for diagnosing type 2N VWD 8.

VWF Propeptide (VWFpp) Assay

• Detects accelerated VWF clearance (type 1C VWD); a VWFpp/VWF:Ag ratio > 3 strongly suggests type 1C [1][5][3][8].
• Only one commercial kit is available; the test is costly and limited to specialized laboratories [1][5].

Genetic Testing – Indications

• Genetic analysis is not part of the routine laboratory work‑up for all suspected VWD cases [1][5]3.
• Indications include: confirming type 2B VWD, distinguishing type 2N VWD from hemophilia A, clarifying uncertain phenotypes, and differentiating type 3 VWD from severe type 1 or type 1C [1][5][6][8].

Pre‑analytical and Timing Considerations

• Testing should be avoided during conditions that transiently raise VWF levels (e.g., stress, vigorous exercise, acute illness, pregnancy, estrogen therapy) [6][8].
• Individuals with blood group O have VWF levels ≈ 25–30 % lower than non‑O groups 6.
• VWF concentrations increase approximately 1–2 % per year with aging 6.
• For patients with heavy menstrual bleeding, defer testing until anemia and active bleeding have resolved 8.
• Repeat testing is often necessary to achieve a definitive diagnosis 8.

Common Pitfalls

• No single laboratory test can diagnose VWD; a comprehensive panel of assays is required [1][2]3.
• Mild VWD may present with completely normal screening results (aPTT, PT, PFA‑100) [2][3].
• The VWF:RCo assay can yield falsely low results in individuals of African ancestry due to the D1472H variant [1][2].
• Because screening tests lack sensitivity for mild disease, clinicians should proceed to specific VWF assays whenever clinical suspicion persists [2][3].

Laboratory Evaluation and Diagnostic Strategy for von Willebrand Disease

Core Diagnostic Panel

• The 2025 guidelines require a mandatory three‑test panel—VWF antigen (VWF:Ag), VWF platelet‑dependent activity measured by VWF:GPIbM (ristocetin‑free) or VWF:GPIbR (with ristocetin), and factor VIII coagulant activity (FVIII:C)—to evaluate suspected von Willebrand disease in any patient population. 9, 10
• No single laboratory assay is sufficient for a definitive VWD diagnosis; the comprehensive panel must be performed together. 9, 10

Preferred VWF Activity Assays

• VWF:GPIbM and VWF:GPIbR assays are recommended over the traditional VWF:RCo because the latter shows poor reproducibility, a high coefficient of variation, and low sensitivity when VWF levels are very low. 9, 10
• The VWF:RCo assay yields falsely low results in approximately 63 % of individuals of African ancestry due to the D1472H polymorphism, leading to misclassification. 9
• The 2025 guidelines explicitly endorse the use of VWF:GPIbM or VWF:GPIbR as the preferred activity tests for VWD evaluation. 9, 10

Routine Platelet and Hemostasis Screening (Limited Utility)

• Complete blood count, including platelet count, is typically normal in patients with VWD, providing little diagnostic value. 9, 10
• The platelet function analyzer (PFA‑100/200) is more sensitive than bleeding time for detecting severe VWD but lacks adequate sensitivity for mild disease; therefore it is not recommended for routine screening and should be reserved for cases of suspected severe VWD. 9, 10
• Bleeding‑time testing has been largely discontinued because it is invasive, poorly reproducible, and insensitive for VWD detection. 9, 10
• Standard coagulation screening (aPTT and PT) is frequently normal in VWD; aPTT may be prolonged in some cases but is often within reference range, especially in mild disease, while PT is typically normal. 9, 10
• When all screening tests are normal but clinical suspicion for VWD remains, specific VWF assays (the core panel) must still be ordered. 9, 10

Specialized Assays for VWD Subtyping

• VWF Multimer Analysis – Essential for distinguishing type 2A from type 2B and other type 2 variants; performed only after abnormal core assay results. 9
• Ristocetin‑Induced Platelet Agglutination (RIPA) – Differentiates type 2A from type 2B VWD, but requires fresh blood, lacks standardization, and is not widely available. 9
• VWF:FVIII Binding Assay (VWF:FVIIIB) – Used to separate type 2N VWD from mild hemophilia A. 9
• VWF Propeptide (VWFpp) Assay – Detects accelerated VWF clearance characteristic of type 1C VWD; a VWFpp/VWF:Ag ratio > 3 strongly suggests this subtype. Only one commercial kit exists, limiting widespread use. 9

Diagnostic Pitfalls and Clinical Recommendations

• Mild VWD may present with completely normal routine screening results (aPTT, PT, PFA‑100), underscoring the need for specific VWF testing when bleeding symptoms are present. 9, 10
• The VWF:RCo assay’s propensity for falsely low values in individuals of African ancestry (due to the D1472H variant) can lead to misdiagnosis; clinicians should preferentially use VWF:GPIbM or GPIbR assays. 9
• Because screening tests lack sensitivity for mild disease, the 2025 guidelines advise proceeding directly to the specific VWF panel whenever clinical suspicion persists despite normal screening. 9, 10

Strength of evidence: The cited statements are derived from the 2025 consensus guidelines published in Blood Advances; specific levels of evidence (e.g., Grade A/B) were not enumerated in the source material.