Collagen-Binding Assay Work-up for Von Willebrand Disease

September 2024
Ampath | ampath.co.za

Overview

Von Willebrand Disease (VWD) is the most common inherited bleeding disorder, affecting approximately 1 in 1,000 people. It is caused by:

• Defects in or reduced levels of Von Willebrand Factor (VWF)

Role of VWF in Haemostasis:

• Carrier protein for Factor VIII
• Facilitates platelet adhesion to vessel walls
• Promotes platelet aggregation

Classification of VWD

✅ Type 1 – Mild Quantitative Defect

• Reduced amount of VWF

✅ Type 2 – Qualitative/Functional Defect

• Normal quantity but defective activity
• Subtypes:
  • Type 2A: Impaired multimerisation (loss of high molecular weight multimers – HMWM)
  • Type 2B: Hyper-functional platelet binding (also with HMWM loss)
  • Type 2M: Decreased GP1b binding
  • Type 2N: Decreased Factor VIII binding

✅ Type 3 – Severe Total Quantitative Defect

• No VWF production

Laboratory Diagnosis of VWD

🧪 Initial Screening Panel (Three Tests):

1. VWF: Antigen (VWF: Ag)
2. VWF: Ristocetin cofactor activity (VWF: RCo)
3. Factor VIII level

🔎 Interpretation by VWF: RCo / VWF: Ag Ratio:

• Type 1 VWD:
  • Proportional reduction in both VWF antigen and activity
  • Ratio: > 0.7
• Type 2 VWD:
  • Discrepant levels: VWF activity is reduced more than antigen
  • Ratio: < 0.7

Role of the Collagen-Binding Assay (VWF: CB)

• Performed when VWF: RCo / VWF: Ag ratio < 0.7 (suggests type 2 VWD)
• Detects binding of high molecular weight multimers (HMWM) to collagen
• Helps differentiate type 2 subtypes:
  • VWF: CB / VWF: Ag ratio < 0.7 suggests Type 2A or 2B VWD

Ampath’s 4-Test VWD Panel Includes:

1. VWF: Ag
2. VWF: RCo
3. Factor VIII
4. Collagen-Binding Assay (VWF: CB) (performed only if needed based on initial results)

Test Information – VWF: CB (Collagen-Binding Assay)

• Mnemonic: VWCB
• Specimen type: Venous blood
• Container: Citrate tube (3.2% trisodium citrate solution)
• Volume required:
  • 9 parts venous blood to 1 part citrate
• Transport instructions:
  • Must reach the lab within 4 hours
  • If delayed: centrifuge, freeze, and send frozen
• Turnaround time: 72 hours
• Indications for testing:
  • Family history of bleeding
  • Mucosal bleeding
  • Easy bruising
  • Epistaxis (nosebleeds)
  • Gingival bleeding
  • Excessive surgical bleeding
  • Heavy menstrual bleeding

📌 For additional support, contact your Ampath haematology consultant or local representative.