What blood tests are used to diagnose von Willebrand disease?

From the Guidelines

The diagnosis of von Willebrand disease typically requires several specialized blood tests, including von Willebrand factor antigen (VWF:Ag), von Willebrand factor activity (VWF:RCo or VWF:GPIbR), and factor VIII activity level, as well as additional tests such as VWF multimer analysis and platelet function tests like PFA-100 closure time. The initial screening may include a complete blood count, prothrombin time, and activated partial thromboplastin time, though these may be normal in mild cases.

• Key tests for diagnosis include:
  • VWF:Ag to measure the amount of VWF protein in blood
  • VWF:RCo or VWF:GPIbR to assess how well the protein functions in platelet binding
  • Factor VIII activity level, as VWF carries and protects factor VIII
• Additional tests that may be performed include:
  • VWF multimer analysis to determine the size distribution of VWF molecules
  • VWF collagen binding assay (VWF:CB) to evaluate another functional aspect of VWF
  • Platelet function tests like PFA-100 closure time
• For definitive typing, VWF propeptide to antigen ratio and genetic testing may be performed, as recommended by the 2008 NHLBI/NIH guidelines 1.
• It is essential to repeat these tests 2-3 times, as levels can fluctuate due to stress, exercise, pregnancy, or inflammation, and testing should be done when the patient is not taking medications that affect platelet function and ideally not during menstruation for female patients, as noted in studies 1.
• The most recent studies, such as those published in 2015, highlight the importance of accurate and sensitive assays for measuring VWF activity, including the use of monoclonal antibody binding-based VWF activity (VWF:Ab) assays, which have been shown to be effective in diagnosing VWD 1.

From the Research

Blood Tests for von Willebrand Disease

The diagnosis of von Willebrand disease (VWD) relies on a combination of clinical features and laboratory testing. The laboratory tests used to diagnose VWD include:

• VWF antigen (VWF:Ag) to assess the level of von Willebrand factor protein in the blood 2
• VWF activity assays, such as:
  • Ristocetin cofactor assay (VWF:RCo) to measure the ability of VWF to bind to platelets in the presence of ristocetin 2, 3
  • Collagen binding (VWF:CB) activity to measure the ability of VWF to bind to collagen 2
  • Platelet glycoprotein (GP) Ib binding activity to measure the ability of VWF to bind to platelet GP Ib 2

Types of VWF Activity Assays

There are several types of VWF activity assays, including:

• Platelet agglutination assays, which measure the ability of VWF to induce platelet agglutination in the presence of ristocetin 3
• Latex agglutination assays, which measure the ability of VWF to induce latex particle agglutination in the presence of ristocetin 3
• Chemiluminescent assay (CLIA), which measures the ability of VWF to bind to recombinant GP Ib 3
• Flow cytometry-based VWF:RCo assay, which measures the ability of VWF to induce platelet aggregation in the presence of ristocetin 4

Automated Assays for VWF:Ag and VWF:RCo

Automated assays for VWF:Ag and VWF:RCo are available, including immunoturbidimetric and chemiluminescent assays 5. These assays have been shown to be precise and comparable between centers, making them suitable for the diagnosis of VWD in non-specialized and reference laboratories.

Laboratory Diagnosis of VWD

The laboratory diagnosis of VWD involves a stepwise approach, including:

• Screening procedures, such as bleeding time, filter tests, platelet counts, and activated partial thromboplastin time (aPTT) 6
• Confirmatory tests, such as VWF:Ag, VWF:RCo, VWF:CB, and ristocetin-induced platelet aggregation (RIPA) 6
• Tests for final classification, such as multimeric analysis and FVIII binding capacity of VWF 6