What labs should I check for spontaneous bruising?

Laboratory Evaluation for Spontaneous Bruising

For patients presenting with spontaneous bruising, initial laboratory evaluation should include complete blood count (CBC) with platelet count, prothrombin time (PT), activated partial thromboplastin time (aPTT), and von Willebrand factor (VWF) assays. 1, 2, 3

First-Line Laboratory Tests

• Complete blood count (CBC) with platelet count

  • Screens for thrombocytopenia and other hematologic abnormalities
  • Essential for ruling out immune thrombocytopenia (ITP), which can be transient and self-resolving 1

• Coagulation studies

  • Prothrombin time (PT) with INR
  • Activated partial thromboplastin time (aPTT)
  • These tests detect most factor deficiencies but not all bleeding disorders 1

• Von Willebrand disease testing

  • VWF antigen (VWF:Ag)
  • VWF ristocetin cofactor activity (VWF:RCo)
  • Factor VIII coagulant activity (FVIII:C)
  • VWD is the most common inherited bleeding disorder but is not reliably detected by PT/aPTT 1, 2

• Fibrinogen concentration and thrombin time

  • Detects rare defects of fibrinogen that can cause significant bleeding 1

Additional Tests Based on Initial Results

If PT is prolonged and aPTT is normal:

• Consider vitamin K deficiency or early liver disease
• Perform vitamin K challenge test 4

If PT is normal and aPTT is prolonged:

• Perform mixing study to differentiate between factor deficiency and inhibitor presence
• Consider specific factor assays for factors VIII, IX, XI 1, 3

If both PT and aPTT are prolonged:

• Evaluate for liver disease with liver function tests
• Consider multiple factor deficiencies or DIC 1

If initial tests are normal but clinical suspicion remains high:

• Consider platelet function testing
  • Platelet aggregation studies (requires specialist interpretation)
  • PFA-100 (can screen for many platelet function disorders and some types of VWD) 1
• Consider testing for factor XIII deficiency (clot solubility test) 1
• Evaluate for fibrinolytic defects (euglobin lysis test) 1

Special Considerations

• Medication review is essential as many medications can cause or worsen bleeding tendencies:

  • Anticoagulants
  • Antiplatelet agents
  • NSAIDs
  • Certain antibiotics 1, 2

• Inflammatory markers (ESR, CRP) should be checked to identify potential underlying inflammatory conditions 1

• Standardized bleeding assessment tool should be used to objectively quantify bleeding history 2

• Vitamin K deficiency should be considered, especially in infants, and can be detected by prolonged PT and possibly aPTT 1

• Repeat testing may be necessary for von Willebrand disease, as levels can vary in response to clinical status 1

When to Refer to Hematology

• When initial testing indicates a bleeding disorder
• When clinical suspicion remains high despite normal initial laboratory results
• For specialized platelet function testing and interpretation 3

Remember that no single laboratory test can definitively screen for all bleeding disorders, and some conditions like mild platelet disorders may require specialized testing under the guidance of a hematologist 1, 2.