What labs are indicated for atypical bleeding?

Laboratory Tests for Atypical Bleeding

For patients with atypical bleeding, initial laboratory evaluation should include complete blood count (CBC), prothrombin time (PT), activated partial thromboplastin time (aPTT), von Willebrand factor antigen (VWF:Ag), von Willebrand factor ristocetin cofactor activity (VWF:RCo), and factor VIII coagulant activity (FVIII). 1, 2

First-Line Testing

Essential Initial Tests:

• Complete Blood Count (CBC) with platelet count
• Prothrombin Time (PT)
• Activated Partial Thromboplastin Time (aPTT)
• Von Willebrand Factor testing:
  • VWF antigen (VWF:Ag)
  • VWF ristocetin cofactor activity (VWF:RCo)
  • Factor VIII coagulant activity (FVIII)
• Fibrinogen levels (Clauss and/or derived method)
• ABO blood group (influences VWF levels)

According to the NHLBI VWD Guidelines, the first three tests (CBC, PT, aPTT) are grade C recommendations, while the three VWF tests are grade B recommendations 1. The International Society on Thrombosis and Haemostasis (ISTH) reports that 100% of surveyed hematologists include PT and aPTT in first-line testing, with 84% including VWF testing 1.

Second-Line Testing

If first-line tests are normal but clinical suspicion remains high:

Platelet Function Tests:

• Light Transmission Aggregometry (LTA) with agonists (epinephrine, ADP, collagen, arachidonic acid, ristocetin)
• Platelet Function Analyzer (PFA-100/200)
• Platelet flow cytometry

Additional Factor Assays:

• Factor II, V, VII, X (extrinsic pathway)
• Factor IX, XI (intrinsic pathway)
• Factor XIII
• VWF multimer analysis (if initial VWF tests are abnormal)

Specialized Tests:

• Fibrinolysis assays
• Thrombin Generation Assay (TGA)
• Thromboelastography (TEG) or Rotational Thromboelastometry (ROTEM)
• Genetic testing for suspected hereditary disorders

The ISTH survey shows that 60% of hematologists include platelet function testing in second-line evaluation, followed by factor assays (52-60%) and genetic testing (48%) 1.

Important Considerations

Sample Handling:

• Transport blood samples for VWF testing at room temperature to prevent cryoprecipitation
• Separate plasma from blood cells quickly at room temperature
• Centrifuge completely to eliminate platelets

Patient Factors That May Affect Results:

• Stress, exercise, inflammation can elevate VWF and FVIII levels
• Pregnancy or estrogen use can mask disorders by elevating VWF
• ABO blood type (type O individuals have approximately 25% lower VWF levels)
• Medications affecting platelet function should be discontinued 7-10 days before testing

Common Pitfalls:

1. Inadequate clinical history: Laboratory results must be interpreted in the context of the patient's bleeding history
2. Improper sample collection: Can lead to falsely prolonged clotting times
3. Testing during acute phase reactions: Can mask underlying bleeding disorders
4. Failure to consider ABO blood type: Type O individuals normally have lower VWF levels
5. Relying solely on screening tests: Up to 60-70% of patients with mild-moderate bleeding may have a bleeding disorder of unknown cause (BDUC) despite normal screening tests 2

Remember that the PFA-100 and skin bleeding time tests are not recommended for initial screening due to insufficient specificity/sensitivity 2.