What blood tests are used to evaluate for bleeding disorders?

Blood Tests for Evaluating Bleeding Disorders

The standard first-line laboratory evaluation for bleeding disorders should include a complete blood count (CBC), prothrombin time (PT), activated partial thromboplastin time (aPTT), and von Willebrand factor (VWF) testing. 1

First-Line Testing

When evaluating a patient for a potential bleeding disorder, the following first-line tests should be ordered:

1. Basic hemostasis tests:

   • Complete blood count (CBC) with platelet count
   • Prothrombin time (PT)
   • Activated partial thromboplastin time (aPTT)

2. Von Willebrand disease (VWD) testing:

   • VWF antigen (VWF:Ag)
   • VWF ristocetin cofactor activity (VWF:RCo)
   • Factor VIII coagulant activity (FVIII)

These tests are recommended by 100% of hemostasis specialists for initial evaluation of bleeding disorders 1. The CBC helps identify thrombocytopenia or anemia, while PT and aPTT can detect coagulation factor deficiencies. VWD testing is essential as it is the most common inherited bleeding disorder and may be missed with only basic coagulation tests 1.

Second-Line Testing

If first-line tests are normal but clinical suspicion remains high, the following second-line tests should be considered:

• Platelet function testing (60% of specialists use this as second-line) 1
• Additional factor assays:
  • Factor II, V, VII, X (extrinsic pathway factors)
  • Factor XIII (60% of specialists test as second-line) 1
• Platelet flow cytometry (42% of specialists) 1
• Fibrinolysis assays (38% of specialists) 1

Specialized Testing

For specific clinical scenarios or when first and second-line testing is inconclusive:

• VWF multimer analysis - only when initial VWD testing identifies abnormalities 1
• Genetic testing - used by 48% of specialists as second-line testing 1
• Thrombin generation assay (28% of specialists) 1

Testing for Specific Bleeding Disorders

Von Willebrand Disease

The most sensitive test for VWD is VWF activity (VWF:RCo), which should be included in the initial evaluation of any patient with mucosal bleeding 1, 2. The combination of VWF activity, bleeding time, and aPTT can identify 92% of VWD patients 2.

Hemophilia and Other Factor Deficiencies

An isolated prolonged aPTT may indicate deficiencies in factors VIII, IX, or XI 3. If aPTT is prolonged, specific factor assays should be performed.

Platelet Disorders

Platelet function disorders may be present despite normal platelet counts. If clinical suspicion is high, platelet function testing should be performed 1.

Common Pitfalls to Avoid

1. Relying solely on PT and aPTT - These tests will miss VWD and many platelet function disorders 1
2. Not considering pre-analytical variables - Ensure proper sample collection and handling
3. Overlooking medication effects - NSAIDs and other medications can affect platelet function
4. Not testing for VWD - Despite being the most common inherited bleeding disorder, VWD is often missed without specific testing 1
5. Using bleeding time or PFA-100 alone - These have limited sensitivity and specificity for VWD screening 1

Special Considerations

• Blood type affects VWF levels - Type O individuals have 25-35% lower VWF levels than non-O individuals 3
• Stress, pregnancy, and inflammation can elevate VWF levels, potentially masking mild VWD 3
• Pediatric patients with suspected bleeding disorders should have VWF activity included in their initial evaluation 2

By following this systematic approach to laboratory testing for bleeding disorders, clinicians can efficiently diagnose the underlying cause of bleeding symptoms and provide appropriate management to reduce morbidity and mortality associated with these conditions.