What labs do I start with for an initial bruising visit?

Initial Laboratory Evaluation for Bruising

For an initial bruising visit, start with a complete blood count (CBC), prothrombin time (PT), and activated partial thromboplastin time (PTT) as the essential first-line laboratory tests. 1, 2

First-Line Laboratory Tests

• Complete Blood Count (CBC) with platelet count

  • Evaluates for thrombocytopenia or other hematologic abnormalities
  • Allows examination of peripheral blood smear
  • Grade C recommendation per NHLBI guidelines 1

• Prothrombin Time (PT)/International Normalized Ratio (INR)

  • Assesses the extrinsic coagulation pathway
  • Grade C recommendation per NHLBI guidelines 1

• Activated Partial Thromboplastin Time (aPTT)

  • Evaluates the intrinsic coagulation pathway
  • Grade C recommendation per NHLBI guidelines 1

When to Add Von Willebrand Disease (VWD) Testing

If the mucocutaneous bleeding history is strong, consider adding these tests during the initial visit 1, 2:

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

These are grade B recommendations per NHLBI guidelines and should be ordered together as they help establish both diagnosis and VWD type/severity if present 1.

Interpretation of Initial Results

• Normal PT and PTT: May indicate platelet disorder (most commonly von Willebrand disease) 3, 4
• Normal PT, prolonged PTT: Suggests deficit in intrinsic pathway; perform mixing study 3, 4
• Prolonged PT, normal PTT: Consider vitamin K deficiency or factor VII deficiency 3
• Both PT and PTT prolonged: Consider liver disease or multiple factor deficiencies 3, 4

Important Collection Considerations

• Transport blood samples for VWF assays at room temperature to prevent cryoprecipitation 1, 2
• Separate plasma from blood cells promptly at room temperature 1
• Centrifuge plasma thoroughly to remove platelets 1

Common Pitfalls to Avoid

1. Patient factors affecting results:

   • Stress, crying in children, or anxiety can falsely elevate VWF and FVIII levels 1, 2
   • Recent exercise can elevate VWF levels 1, 2
   • Inflammatory illness, pregnancy, or estrogen use can elevate VWF and FVIII 1, 2
   • Blood group O individuals have VWF levels ~25% lower than other blood groups 1, 2

2. Test limitations:

   • PFA-100 and bleeding time tests are not recommended for routine screening due to insufficient sensitivity/specificity 1, 2
   • VWF multimer analysis should not be used for initial screening but only if initial VWD testing identifies abnormalities 1

3. Timing considerations:

   • Medications affecting platelet function should be discontinued 7-10 days before testing 2

If initial testing is normal but clinical suspicion remains high, referral to a hematologist is recommended for specialized testing 2, 4.

By following this systematic approach to laboratory evaluation of bruising, you can efficiently identify or rule out common bleeding disorders while avoiding unnecessary testing.