What laboratory tests should be ordered for a patient presenting with easy bruising?

Laboratory Workup for Easy Bruising

Order a complete blood count (CBC) with platelet count and peripheral smear, PT/INR, aPTT, and fibrinogen as your initial screening panel for any patient presenting with easy bruising. 1, 2, 3

Initial Screening Tests (First-Line)

The following tests evaluate for the most common bleeding disorders with prevalence greater than 1 per 500,000 people:

• CBC with platelet count and peripheral smear screens for thrombocytopenia (including ITP), thrombocytosis, and platelet morphology abnormalities 1, 2, 3
• Prothrombin time (PT/INR) evaluates the extrinsic coagulation pathway and vitamin K-dependent factors 1, 2, 3
• Activated partial thromboplastin time (aPTT) assesses the intrinsic coagulation pathway and can detect hemophilia and some cases of von Willebrand disease 1, 2, 3
• Fibrinogen level identifies fibrinogen disorders and helps rule out disseminated intravascular coagulation 1, 2

Von Willebrand Disease-Specific Testing

If the patient has strong mucocutaneous bleeding symptoms (nosebleeds, heavy menstrual bleeding, gum bleeding, prolonged bleeding from minor cuts), proceed directly to VWD testing even if PT/aPTT are normal. 1, 4, 2

The three essential VWD tests that must be ordered together are:

• VWF antigen (VWF:Ag) measures the quantity of von Willebrand factor protein 1, 4, 2
• VWF ristocetin cofactor activity (VWF:RCo) assesses functional platelet binding ability 1, 4, 2
• Factor VIII coagulant activity (FVIII) evaluates factor VIII levels, which are stabilized by VWF 1, 4, 2

These three tests establish both diagnosis and VWD subtype, with abnormal results defined as low individual values or a VWF:RCo to VWF:Ag ratio below 0.5-0.7. 1, 4

Algorithmic Approach Based on Initial Results

Normal PT and aPTT: Suspect platelet dysfunction or von Willebrand disease—proceed to VWD-specific testing 3, 5

Prolonged aPTT with normal PT: Indicates intrinsic pathway defect (factors VIII, IX, XI deficiency or VWD)—order VWD panel and consider hemophilia workup 1, 3, 5

Prolonged PT with normal aPTT: Suggests extrinsic pathway defect or vitamin K deficiency—consider vitamin K challenge 3, 5

Both PT and aPTT prolonged: Evaluate for liver disease, vitamin K deficiency, or disseminated intravascular coagulation 3, 5

Isolated thrombocytopenia: Consider ITP, drug-induced thrombocytopenia, or bone marrow disorders 1

Critical Pitfalls to Avoid

• Do not rely solely on PT/aPTT to exclude bleeding disorders—these tests will miss von Willebrand disease (the most common inherited bleeding disorder affecting up to 1% of the population) and platelet function disorders 1, 4, 2

• Do not order VWF multimer analysis as initial screening—this complex test should only be performed when initial VWD testing shows abnormalities or discrepant VWF:RCo/VWF:Ag ratios 1, 4

• Do not order PFA-100 or bleeding time tests routinely—these have conflicting sensitivity/specificity data and are not recommended for screening 1, 4

• Avoid testing during conditions that falsely elevate VWF levels—stress, inflammation, pregnancy, and estrogen therapy can mask VWD 4, 6

• Remember blood type O individuals have 25% lower baseline VWF levels—interpret results accordingly 4, 6

Special Considerations for Pediatric Patients

In children with easy bruising, also consider:

• Serum calcium, phosphorus, alkaline phosphatase to screen for bone metabolism disorders 2
• Parathyroid hormone and 25-hydroxy-vitamin D for metabolic bone disease 2
• Serum copper and ceruloplasmin for copper deficiency 2
• Careful assessment for non-accidental trauma—bleeding disorders do not resolve with change of caregivers, whereas abuse-related bruising typically does 1

When to Consult Hematology

Refer to a hematologist when:

• Initial screening tests reveal abnormalities suggesting a bleeding disorder 3, 5
• Clinical suspicion remains high despite normal laboratory results 3, 5
• VWD testing shows abnormal results requiring specialized testing or multimer analysis 1, 4
• Patient has positive bleeding history with increasing number of affirmative responses to structured bleeding questionnaires 1