What lab tests are recommended for evaluating easy bruising?

Laboratory Tests for Evaluating Easy Bruising

For patients with easy bruising, initial laboratory evaluation should include a complete blood count (CBC), prothrombin time (PT), activated partial thromboplastin time (aPTT), and von Willebrand factor (VWF) assays. 1, 2

Initial Evaluation Algorithm

1. First-line laboratory tests:

   • Complete blood count (CBC) with platelet count
   • Peripheral blood smear
   • Prothrombin time (PT) with INR
   • Activated partial thromboplastin time (aPTT)
   • Fibrinogen level 2, 3

2. If mucocutaneous bleeding pattern is prominent, add:

   • VWF antigen (VWF:Ag)
   • VWF ristocetin cofactor activity (VWF:RCo)
   • Factor VIII coagulant activity (FVIII) 1

Interpretation of Initial Test Results

• Normal PT and aPTT with abnormal bleeding: Suggests platelet dysfunction or von Willebrand disease 3, 4
• Normal PT with prolonged aPTT: Indicates disorder in the intrinsic coagulation pathway (factors VIII, IX, XI, XII) - proceed with mixing studies 3, 4
• Prolonged PT with normal aPTT: Suggests disorder in the extrinsic pathway (factor VII) or vitamin K deficiency 4
• Both PT and aPTT prolonged: Consider liver disease, vitamin K deficiency, or disseminated intravascular coagulation 4, 5
• Low platelet count: Evaluate for thrombocytopenia causes (immune thrombocytopenia, bone marrow disorders, medication effects) 5

Additional Testing Based on Initial Results

If von Willebrand disease is suspected:

• If VWF:RCo or VWF:Ag is abnormally low, or if the ratio of VWF:RCo to VWF:Ag is below 0.5-0.7, proceed with:
  • VWF multimer analysis
  • Ristocetin-induced platelet aggregation (RIPA) 1, 2

If platelet dysfunction is suspected:

• Platelet function tests
• Platelet aggregation studies 6

If coagulation factor deficiency is suspected:

• Specific factor assays based on which pathway is abnormal 4

Common Pitfalls and Caveats

1. Pre-analytical variables affecting results:

   • Recent exercise, stress, or pregnancy can increase VWF levels and mask mild deficiencies
   • Blood collection technique can affect platelet function tests
   • Medications (especially NSAIDs, antiplatelet drugs) can cause platelet dysfunction 1, 6

2. Timing considerations:

   • VWF is an acute phase reactant and may be falsely normal during illness or stress
   • Multiple tests may be needed to confirm diagnosis, especially for von Willebrand disease 1

3. Special populations:

   • Consider thyroid function tests in patients with unexplained easy bruising, as both Graves' disease and Hashimoto's thyroiditis can be associated with platelet abnormalities and easy bruising 7
   • In children or vulnerable populations, consider non-accidental trauma as a cause of bruising 3

4. When to refer:

   • If initial testing is normal but clinical suspicion remains high
   • If a specific bleeding disorder is identified and requires specialized management
   • If bleeding symptoms are severe or persistent despite normal initial testing 3, 4

Remember that bleeding assessment tools can help quantify bleeding symptoms and determine the need for laboratory evaluation. The International Society on Thrombosis and Hemostasis bleeding assessment tool is particularly useful for identifying patients who require further testing 4.