What is the initial test for von Willebrand disease?

Initial Testing for von Willebrand Disease

The initial laboratory evaluation for von Willebrand disease should include three specific tests: VWF antigen (VWF:Ag), VWF ristocetin cofactor activity (VWF:RCo), and factor VIII coagulant activity (FVIII). 1

Primary Testing Panel

• VWF antigen (VWF:Ag) - measures the quantity of von Willebrand factor protein in plasma 1
• VWF ristocetin cofactor activity (VWF:RCo) - assesses the functional ability of VWF to bind to platelets 1
• Factor VIII coagulant activity (FVIII) - evaluates the level of factor VIII, which is carried and protected by VWF 1

These three tests are considered grade B recommendations by the 2008 NHLBI/NIH guidelines and should be ordered together as the initial evaluation panel when VWD is suspected 1.

Testing Algorithm

1. Begin with clinical assessment for bleeding risk:

   • If mucocutaneous bleeding history is strong, proceed directly to VWD-specific testing 1
   • For patients with less clear presentation, initial hemostasis tests (CBC, PT, PTT) may be ordered first 1

2. Order all three initial VWD tests (VWF:Ag, VWF:RCo, FVIII) simultaneously 1

   • These tests not only help establish diagnosis but also suggest type and severity of VWD if present 1

3. Interpret results:

   • Abnormally low values in any of these tests may indicate VWD 1
   • The ratio of VWF:RCo to VWF:Ag is particularly important - a ratio below 0.5-0.7 suggests type 2 VWD 1, 2

Important Considerations

• VWF multimer analysis is NOT recommended for initial screening but should be reserved for cases where initial testing shows abnormalities 1

• Bleeding time and platelet function analyzer (PFA-100) tests are sometimes used but have conflicting data regarding sensitivity and specificity; current evidence does not support their routine use as screening tests 1

• Testing should ideally be performed in the absence of conditions that elevate baseline VWF (such as pregnancy, inflammation, or stress) 1

• Laboratory variability can affect results, so careful attention to blood specimen collection, processing, transportation, and storage is essential 1

Common Pitfalls to Avoid

• Relying on a single test for VWD diagnosis - no single laboratory test can screen for all forms of VWD 1, 3

• Ordering VWF multimer analysis as part of initial screening - this complex test should be reserved for reflex testing when initial results are abnormal 1

• Failing to consider timing of testing - VWF levels can be affected by various physiological and pathological conditions 1

• Misinterpreting mildly decreased VWF levels (30-50% of normal) - these require correlation with clinical assessment and family history of bleeding 1, 2

For patients with abnormal initial test results, consultation with a hemostasis specialist is recommended for further evaluation and management 1.