Von Willebrand Disease Type 2 Diagnosis with vWF 0.93 and Antigen Activity Ratio of 0.7
A von Willebrand factor (vWF) level of 0.93 does NOT rule out type 2 von Willebrand disease when the antigen activity ratio is 0.7, as type 2 VWD is primarily diagnosed by a low VWF:RCo/VWF:Ag ratio (<0.5-0.7), regardless of the absolute vWF level. 1
Understanding VWD Type 2 Diagnosis
Type 2 VWD is characterized by qualitative defects in vWF function rather than just quantitative deficiency. The key diagnostic features include:
- VWF:RCo/VWF:Ag ratio: A ratio below 0.5-0.7 strongly suggests type 2 VWD, even when individual values appear normal 1, 2
- Normal vWF levels: Type 2 VWD can present with normal vWF antigen levels (30-200 IU/dL) but functional defects 1
- Multimer analysis: Different patterns distinguish between subtypes 2A, 2B, 2M, and 2N 3
Your Specific Case Analysis
With a vWF level of 0.93 (93%) and an antigen activity ratio of 0.7:
- The vWF level is within normal range, which is common in type 2 VWD
- The antigen activity ratio of 0.7 is at the borderline cutoff for diagnosing type 2 VWD
- This pattern is most consistent with type 2M VWD, which often shows normal or near-normal multimer patterns but decreased VWF activity relative to antigen levels 3
Diagnostic Algorithm for Type 2 VWD
Initial screening:
- Assess VWF:Ag and VWF activity (VWF:RCo)
- Calculate VWF:RCo/VWF:Ag ratio
Interpretation:
- Ratio >0.7: Type 2 VWD unlikely
- Ratio 0.5-0.7: Borderline, consider type 2 VWD (especially 2M)
- Ratio <0.5: Strong evidence for type 2 VWD
Further testing for borderline cases:
- VWF multimer analysis
- Ristocetin-induced platelet aggregation (RIPA)
- Collagen binding assay (VWF:CB)
- Genetic testing for confirmation
Common Pitfalls in Diagnosis
- Overreliance on absolute vWF levels: Type 2 VWD diagnosis depends on the activity-to-antigen ratio, not absolute levels 2
- Stress-induced elevation: VWF is an acute phase reactant that can be falsely elevated during stress, masking underlying defects 1
- Single testing: The American Academy of Pediatrics notes that VWF testing may need to be repeated up to 3 times for reliable results 1
- Missing subtle variants: Type 2M VWD is frequently misdiagnosed as type 1 or 2A VWD 2
Conclusion for Clinical Decision Making
The doctor's statement that a vWF level of 0.93 makes type 2 VWD impossible is incorrect based on current guidelines. The antigen activity ratio of 0.7 places this case at the borderline for type 2 VWD diagnosis, most likely type 2M. Further specialized testing including multimer analysis and possibly genetic testing would be appropriate to confirm the diagnosis.