Von Willebrand Factor (VWF) Level Test
von Willebrand Factor (VWF) Level Testing
Key Points
- Essential for diagnosing von Willebrand Disease (VWD)
- Comprises multiple assays for comprehensive assessment
- Age and blood type influence reference ranges
- Requires careful timing and sample handling
Overview
VWF testing is a complex panel of laboratory assessments designed to evaluate both quantitative and qualitative aspects of von Willebrand Factor, crucial for proper hemostasis and platelet function.
Core VWF Assays
- VWF Antigen (VWF:Ag)
- Measures total VWF protein quantity
- Normal range: 50-200 IU/dL
- Basic screening test for VWD
- VWF Activity Assays
- VWF:RCo (Ristocetin Cofactor Activity)
- Measures functional ability to bind platelets
- Gold standard for VWF function
- Normal range: 50-200 IU/dL
- VWF:GPIbR (Gain-of-function GPIb binding assay)
- Alternative to VWF:RCo
- More precise and reproducible
- Less affected by technical variables
- VWF:RCo (Ristocetin Cofactor Activity)
- VWF:CB (Collagen Binding)
- Assesses binding to subendothelial collagen
- Important for high molecular weight multimer function
- Helps differentiate VWD subtypes
Additional Specialized Tests
- VWF Multimer Analysis
- Evaluates size distribution of VWF molecules
- Critical for typing VWD variants
- Complex technical requirements
- FVIII:C (Factor VIII Activity)
- Often included in VWF assessment
- Reflects VWF's carrier function
- Important for phenotype assessment
Diagnostic Applications
- Primary VWD Diagnosis
- Initial screening
- Type differentiation
- Severity assessment
- Monitoring
- Treatment response
- Prophylaxis adequacy
- Perioperative management
- Risk Assessment
- Preoperative evaluation
- Bleeding risk stratification
- Family screening
Specific Clinical Scenarios
- Unexplained bruising or bleeding
- Family history of bleeding disorders
- Preoperative assessment
- Heavy menstrual bleeding in adolescents
- Excessive bleeding after minor procedures
Age-Specific Considerations
- Neonates and Infants
- Higher baseline levels
- Age-specific reference ranges crucial
- Developmental hemostasis impact
- Children and Adolescents
- Gradual normalization to adult ranges
- Puberty-related changes
- Activity level considerations
Result Patterns and Significance
- Type 1 VWD Pattern
- Proportional reduction in VWF:Ag and activities
- Normal multimer distribution
- VWF:RCo/VWF:Ag ratio > 0.7
- Type 2 VWD Patterns
- Discordant activity and antigen levels
- Abnormal multimer patterns
- Variant-specific characteristics
- Type 3 VWD Pattern
- Virtually absent VWF
- Very low FVIII
- No detectable multimers
Preanalytical Variables
- Sample Collection
- Proper citrate concentration
- Fill volume requirements
- Temperature control
- Processing time limits
- Patient Factors
- Recent exercise
- Stress levels
- Time of day
- Medications
Quality Assurance
- Laboratory Standards
- Method validation
- Internal quality control
- External quality assessment
- Result Verification
- Repeat testing protocols
- Critical value handling
- Result correlation
