von Willebrand Disease - VWD

Indications for Testing

• Initial evaluation (personal/family history and physical examination) suggestive of a bleeding disorder

Laboratory Testing

• Initial testing
  • Important to evaluate other potential causes of mucocutaneous bleeding
    • Disorders of the liver, kidneys, blood, or bone marrow
    • Undiagnosed thrombocytopenia (type 2B and platelet-type von Willebrand disease [PT-VWD] may have thrombocytopenia)
    • Anti-platelet medications (aspirin, NSAIDs, clopidogrel, others)
  • Initial evaluation for a bleeding disorder (to exclude other coagulation defects)
    • CBC with platelet count
      • VWD type 2B and platelet type may have thrombocytopenia
    • Prothrombin time/partial thromboplastin time (PT/PTT)
    • Fibrinogen, or thrombin time (TT)
      • Fibrinogen or TT are optional (ASH, 2012)
  • In the presence of a strong history of mucocutaneous bleeding, tests for VWD could be considered as part of the initial evaluation
  • VWD may prolong the PTT – it is a carrier for factor VIII
  • PTT often normal in VWD
  • If PTT abnormal, PTT mixing studies may be useful in the initial evaluation to differentiate factor deficiency from inhibitor as cause of prolonged PTT
    • In VWD, decreased factor VIII may result in a prolonged PTT that corrects with mixing study
  • Refer to Anticoagulants and Possible Coagulation Test Interferences table for possible interferences with coagulation parameters based on the specific drug administered
• VWD testing
  • Initial testing
    • VWF antigen (VWF:Ag) – measures the amount of protein
    • VWF ristocetin cofactor activity (VWF:Rco) – measures the function of the protein
    • Factor VIII activity – measures amount of protein
  • Selected special testing  – usually used for subtyping
    • Multimeric analysis
      • Shows the distribution of different-sized multimers
      • Not recommended for initial screening except in suspected cases of acquired VWD
        • Multimeric abnormalities may be the only abnormality identified in some cases of acquired VWD
      • Types 2A, 2B, and platelet type and acquired cases have abnormal multimeric distributions
      • Abnormal result defined as absence of high- and/or intermediate-molecular-weight multimers
    • VWF:Rco to VWF:Ag ratio
      • VWD types 2A, 2B, platelet type, and 2M characteristically have lower levels of VWF:Rco compared to VWF:Ag, resulting in a decreased VWF:Rco-to-VWF:Ag ratio
        • Ratios <0.7 or <0.6 suggest one of these qualitative subtypes
    • Ristocetin-induced platelet aggregation (RIPA)
      • Not sensitive to mild forms of VWD (most type 1 cases)
      • Typically used to confirm and distinguish between type 2 subtypes (2A, 2B/platelet type)
        • Low-dose RIPA detects abnormally increased aggregation seen in type 2B and platelet-type VWD
    • vWF:platelet binding
      • Detects abnormally increased platelet binding seen in type 2B
      • Differentiates type 2B from platelet-type VWD
        • Test is normal in platelet type
    • VWF:FVIII binding
      • Differentiates between type 2N and hemophilia A
        • Test is normal in hemophilia A
    • Genetic/molecular testing
      • Confirm phenotypic diagnosis of VWD where it affects therapeutic decisions
      • Distinguish VWD type 2B from platelet-type VWD
      • Distinguish VWD type 2N from hemophilia A
      • Evaluate family members of individuals with known mutations
  • Expected laboratory values in VWD by subtype

    Expected Laboratory Values in VWD by Subtype (derived from Favaloro, 2014)
    Type	1	2A	2B	2M	2N	3
    VWF:Ag	Mild to moderate decrease	Frequently mild to moderate decrease	Normal to moderate decrease	Mild to severe decrease	Normal to moderate decrease	Marked decrease or absence
    VWF:RCo	Mild to moderate decrease	Moderate to severe decrease	Mild to severe decrease	Mild to severe decrease	Normal to moderate decrease	Marked decrease or absence
    FVIII	Normal to moderate decrease	Normal to moderate decrease	Normal to moderate decrease	Normal to moderate decrease	Mild to severe decrease	Marked decrease (<10) or absence
    Platelet count	Normal	Usually normal	Often slightly low; exacerbated by surgery, stress, pregnancy	Normal	Normal	Normal
    Multimer pattern	Normal pattern, but reduced intensity	Abnormal; loss of HMW and intermediate-weight (IMW) multimers	Abnormal; loss of HMW multimers	Normal	Normal	No VWF present
    * RIPA	Often normal	Reduced aggregation at high ristocetin concentrations	Abnormal; enhanced aggregation at low ristocetin concentrations	Reduced at high ristocetin concentrations	Normal	Absent
    +VWF:FVIII binding	Normal	Normal	Normal	Normal	Decreased	NA
    RCo:Ag ratio	Normal (>0.5-0.7)	Decreased (<0.5-0.7)	Decreased or normal (usually <0.5-0.7)	Decreased (<0.5-0.7)	Normal (>0.5-0.7)	NA
    * RIPA must be performed by a local laboratory due to limited stability of specimen + Measures ability of VWF to bind to factor VIII
• Factors that may affect laboratory testing in VWD
  • VWF values fluctuate over time
    • If clinical suspicion is high and values are normal, repeat testing may be required for diagnosis
  • With mild disease – may have normal test results
  • Mildly decreased VWF values are not diagnostic
  • VWF and FVIII are acute phase reactants and may be elevated by stress, illness, or medications (false-negative)
    • Conditions include pregnancy, estrogen-containing medications, inflammation, infection, liver disease, malignancy, exercise, stress/anxiety, and trauma (including traumatic venipuncture)
  • VWF values and FVIII activity are affected by ABO blood type
    • Type O individuals have ~25% lower values than non-ABO individuals
  • VWF and FVIII results can be affected by preanalytical variables such as collection technique, specimen preparation, storage, and transport
    • Cold storage of citrated whole blood prior to centrifugation
      • Can markedly reduce VWF and FVIII values
      • Can also induce multimeric abnormalities
      • Can lead to incorrect diagnosis or subtyping

Differential Diagnosis

• Functional platelet disorders
• Hemophilia A or other coagulation factor deficiencies
• Underlying malignancy (cause of acquired VWD)
  • Lymphoproliferative disease
    • B-cell lymphoma
    • T/NK-cell lymphoma
  • Myeloproliferative neoplasms
  • Leukemia
    • Acute myeloid leukemia
    • Acute lymphoblastic leukemia