Will a Complete Blood Count (CBC) indicate if an increase in bruising is worrisome?

CBC's Role in Evaluating Increased Bruising

A Complete Blood Count (CBC) is an essential first-line test for evaluating increased bruising, but it only detects certain causes such as thrombocytopenia and cannot identify many bleeding disorders that require additional specialized testing. 1

What a CBC Can Detect

• Platelet count abnormalities:

  • Thrombocytopenia (<150,000/μL) is a common cause of increased bruising 2, 1
  • The CBC confirms the presence and severity of thrombocytopenia 3

• Other hematologic abnormalities:

  • Leukemia or other bone marrow disorders that may present with bruising 4
  • Anemia that may accompany certain bleeding disorders 3

What a CBC Cannot Detect

• Von Willebrand Disease (VWD): The most common inherited bleeding disorder requires specific testing beyond CBC 1, 5

• Coagulation factor deficiencies: Many factor deficiencies will not be detected by CBC alone 2

• Platelet function disorders: Patients may have normal platelet counts but abnormal platelet function 2, 1

Appropriate Testing Algorithm for Increased Bruising

1. Initial evaluation with CBC to assess for thrombocytopenia or other hematologic abnormalities 1, 5

2. If CBC is normal but clinical suspicion remains high:

   • Prothrombin Time (PT) and activated Partial Thromboplastin Time (aPTT) should be ordered 2, 5
   • Von Willebrand factor testing (VWF:Ag, VWF:RCo, and Factor VIII activity) 1

3. If initial coagulation tests are abnormal:

   • Abnormal PT with normal aPTT: Consider vitamin K deficiency 5
   • Normal PT with prolonged aPTT: Consider intrinsic pathway defect; mixing study indicated 5
   • Both PT and aPTT prolonged: Consider liver failure workup 5

4. If all initial tests are normal but clinical suspicion remains high:

   • Referral to a hematologist for specialized testing 1, 5
   • Platelet function testing may be required 2

Clinical Considerations

• The pattern of bruising provides important diagnostic clues:

  • Mucocutaneous bleeding suggests platelet dysfunction 5
  • Hemarthroses or deep hematomas suggest coagulopathy 5

• Medical conditions associated with increased bruising that may not be detected by CBC:

  • Thyroid disorders (Graves' disease, Hashimoto's thyroiditis) can cause elevated platelet IgG and easy bruising 6
  • Ehlers-Danlos syndrome, scurvy, and other medical conditions 2

Common Pitfalls to Avoid

• Relying solely on CBC: Many bleeding disorders present with normal CBC results 2, 1

• Overlooking medication effects: Many medications can cause increased bruising without affecting CBC parameters 2, 5

• Misinterpreting abnormal results: Specimen handling can lead to false-positive coagulation test results 2

• Failing to repeat testing: Von Willebrand factor levels can vary with clinical status and may require repeated testing 2

In summary, while CBC is an important first step in evaluating increased bruising, clinicians should recognize its limitations and be prepared to pursue additional testing when clinically indicated.