Is a von Willebrand factor level of 0.82 considered normal and does it rule out von Willebrand disease?

Von Willebrand Factor Level of 0.82 and Von Willebrand Disease

A von Willebrand factor level of 0.82 (82 IU/dL) is within the normal range and generally rules out von Willebrand disease, though it does not completely exclude type 2 variants that have qualitative defects rather than quantitative deficiencies.

Understanding VWF Levels and Normal Ranges

Von Willebrand factor (VWF) levels are typically reported in international units per deciliter (IU/dL) or as a percentage of normal. The interpretation of VWF levels must consider several important factors:

• Normal VWF levels generally range from 0.50-2.00 IU/dL (50-200%)
• Blood type significantly affects VWF levels - individuals with blood type O have VWF levels approximately 25% lower than other blood groups 1
• VWF is an acute phase reactant that can be elevated by:
  • Stress, anxiety, or crying in children
  • Recent exercise
  • Acute or chronic inflammatory conditions
  • Pregnancy
  • Estrogen/oral contraceptives 2

Diagnosing Von Willebrand Disease

The diagnosis of VWD requires more than just a single VWF level measurement. According to the 2008 NHLBI/NIH guidelines, no single laboratory test can definitively screen for VWD 2, 1. The diagnostic approach should include:

1. Initial VWD assays:

   • VWF antigen (VWF:Ag)
   • VWF activity (VWF:RCo or other platelet-binding assays)
   • Factor VIII coagulant activity (FVIII:C)
   • Calculation of VWF:RCo/VWF:Ag ratio 2

2. Interpretation of results:

   • Type 1 VWD: VWF:RCo and VWF:Ag both reduced (<30 IU/dL), with normal ratio (>0.5-0.7)
   • Type 2 VWD: VWF:RCo disproportionately decreased compared to VWF:Ag, with ratio <0.5-0.7
   • Type 3 VWD: Severe deficiency of VWF (typically <10 IU/dL) 2, 1

Significance of a 0.82 VWF Level

With a VWF level of 0.82 (82 IU/dL):

• This value falls within the normal reference range
• It is well above the typical cutoff of <30 IU/dL used to diagnose type 1 VWD
• However, it does not completely rule out type 2 variants of VWD, which are characterized by qualitative defects 2, 1

Important Considerations

1. Laboratory variability:

   • The VWF:RCo assay has a high coefficient of variation (10-30%)
   • Results can vary between laboratories
   • Proper sample handling is critical - samples must be processed at room temperature and promptly frozen 2, 1

2. Type 2 VWD possibility:

   • Even with normal or borderline VWF levels, type 2 variants can still be present
   • The key diagnostic feature of type 2 VWD is a reduced VWF:RCo/VWF:Ag ratio (<0.5-0.7)
   • Additional testing including VWF multimer analysis may be needed if clinical suspicion remains high 2, 1

3. Clinical correlation:

   • Bleeding symptoms should always be considered alongside laboratory values
   • A standardized bleeding assessment tool (BAT) can help quantify bleeding history objectively 1
   • Mild bleeding symptoms are common in healthy populations and may have causes other than VWF defects 3

When Further Testing Is Warranted

Despite a normal VWF level of 0.82, additional testing should be considered if:

• There is a significant personal or family history of bleeding
• The patient has characteristic bleeding symptoms (mucosal bleeding, heavy menstrual bleeding, etc.)
• There is a known family history of VWD 2, 1

In such cases, a complete VWD panel including VWF:RCo/VWF:Ag ratio calculation and possibly VWF multimer analysis would be appropriate to rule out type 2 variants.

Conclusion

While a VWF level of 0.82 is within normal range and makes type 1 VWD unlikely, it's important to remember that VWD diagnosis requires comprehensive evaluation including activity assays and ratio calculations, especially to exclude type 2 variants that have qualitative rather than quantitative defects.