Blood Tests for Evaluating Bleeding Disorders
The essential first-line laboratory tests for evaluating bleeding disorders include complete blood count (CBC), prothrombin time (PT), activated partial thromboplastin time (aPTT), and von Willebrand factor (VWF) assays. 1
First-Line Testing
Basic Hemostatic Tests
- Complete Blood Count (CBC) - Evaluates for thrombocytopenia and anemia 1
- Peripheral Blood Smear - Assesses platelet morphology and size 1
- Prothrombin Time (PT) - Evaluates extrinsic and common coagulation pathways 1
- Activated Partial Thromboplastin Time (aPTT) - Evaluates intrinsic and common coagulation pathways 1
- Fibrinogen Level - Typically Clauss method (90% of centers use this in first-line testing) 1
Von Willebrand Disease Testing
- VWF Antigen (VWF:Ag) - Measures quantity of VWF protein 1
- VWF Ristocetin Cofactor Activity (VWF:RCo) - Measures VWF function 1
- Factor VIII Coagulant Activity (FVIII) - Often decreased in VWD 1
Additional First-Line Tests
- ABO Blood Group - Affects VWF levels (70% of centers include this) 1
- Iron Studies - Important as iron deficiency can affect bleeding (69% of centers) 1
- Factor VIII, IX, and XI Assays - Evaluates for hemophilia and other factor deficiencies (62% of centers) 1
Second-Line Testing
When first-line tests are normal but clinical suspicion remains high:
Platelet Function Testing
- Light Transmission Aggregometry - Gold standard for platelet function disorders (60% of centers use as second-line) 1
- Platelet Function Analyzer (PFA-100/200) - Screens for platelet dysfunction 1
- Platelet Flow Cytometry - Evaluates platelet surface receptors (42% of centers) 1
Additional Factor Assays
- Factor XIII Assay - 60% of centers include in second-line testing 1
- Factors II, V, VII, X - Each tested by >50% of centers in second-line evaluation 1
Specialized Tests
- VWF Multimer Analysis - Evaluates structure of VWF multimers to determine VWD subtype 1
- Fibrinolysis Assays - Evaluates for disorders of clot breakdown (38% of centers) 1
- Thrombin Generation Assay - Provides global assessment of coagulation (28% of centers) 1
- Genetic Testing - For suspected hereditary disorders (48% of centers use as second-line) 1
Interpretation of Results
PT/aPTT Patterns
- Normal PT, Prolonged aPTT - Suggests deficiency in intrinsic pathway factors (VIII, IX, XI) or presence of inhibitor 2
- Prolonged PT, Normal aPTT - Suggests deficiency in extrinsic pathway factors (VII) 3
- Both PT and aPTT Prolonged - Consider liver disease, vitamin K deficiency, or DIC 3
Von Willebrand Disease Evaluation
- VWF:RCo is the most sensitive test for VWD diagnosis (79% sensitivity) 4
- The combination of VWF:RCo, bleeding time, and aPTT identifies 92% of VWD patients 4
- VWF:RCo to VWF:Ag ratio <0.5-0.7 suggests qualitative VWF defect (Type 2 VWD) 1
Common Pitfalls to Avoid
- Failing to consider preanalytical variables - Proper sample collection and handling is crucial for accurate results
- Not accounting for physiologic variables - VWF levels are affected by blood type, stress, pregnancy, and thyroid function 1
- Relying solely on screening tests - Normal PT and aPTT do not rule out common bleeding disorders like VWD or platelet function disorders 2
- Overlooking medication effects - Many medications affect platelet function and should be documented
- Single testing only - Some bleeding disorders may require repeat testing due to variability in test results
Special Considerations
- Pediatric Patients - Consider specialized bleeding assessment tools for children 1
- Bleeding of Unknown Cause - 75% of specialists register patients with convincing bleeding history even with normal laboratory tests 1
- Pre-surgical Screening - Targeted testing based on bleeding history is more valuable than universal screening 1
By following this systematic approach to laboratory evaluation of bleeding disorders, clinicians can efficiently diagnose the underlying cause and guide appropriate management to reduce morbidity and mortality associated with bleeding complications.