What labs should be checked for abnormal bruising?

Laboratory Tests for Abnormal Bruising

For patients with abnormal bruising, the initial laboratory workup should include a complete blood count (CBC) with platelets, prothrombin time (PT)/INR, activated partial thromboplastin time (aPTT), and if mucocutaneous bleeding is present, von Willebrand disease testing. 1

First-Line Laboratory Tests

• Complete blood count (CBC) with platelets and peripheral blood smear to evaluate for thrombocytopenia or abnormal platelet morphology 1, 2
• Prothrombin time (PT)/INR to assess the extrinsic coagulation pathway 1, 3
• Activated partial thromboplastin time (aPTT) to evaluate the intrinsic coagulation pathway 1, 4
• Fibrinogen level to assess for fibrinogen disorders 1, 3

Von Willebrand Disease Testing

If mucocutaneous bleeding is prominent or initial tests are normal but clinical suspicion remains high, von Willebrand disease testing should be performed:

• Von Willebrand factor antigen (VWF:Ag) 5
• Von Willebrand factor ristocetin cofactor activity (VWF:RCo) 5
• Factor VIII coagulant activity (FVIII) 5

These three tests are recommended for initial VWD evaluation, as they can establish the diagnosis and suggest the type and severity of VWD if present 5.

Additional Testing Based on Initial Results

• If one or more VWD test results are abnormally low and/or if the ratio of VWF:RCo to VWF:Ag is abnormally low (below 0.5–0.7), specialized VWD assays should be considered 5
• VWF multimer analysis should only be performed if initial VWD testing identifies an abnormal result or clinical information suggests a high likelihood of abnormal VWF multimer analysis 5, 6
• For children with easy bruising, consider testing for bone metabolism disorders with serum calcium, phosphorus, alkaline phosphatase, parathyroid hormone, 25-hydroxy-vitamin D, serum copper, and ceruloplasmin 1

Specialized Testing for Persistent Unexplained Bleeding

If initial testing is normal but clinical suspicion remains high:

• Platelet function testing using light transmission aggregometry with multiple agonists (ADP, collagen, epinephrine, ristocetin, arachidonic acid) 6
• Platelet flow cytometry to evaluate platelet surface glycoproteins and activation markers 6
• Factor XIII activity testing, as it is often overlooked in routine coagulation panels 6
• Rare coagulation factor assays (FII, FV, FVII, FX), especially with a family history pattern 6

Common Pitfalls to Avoid

• Relying solely on PT and aPTT to rule out bleeding disorders will miss von Willebrand disease and mild platelet function disorders 1, 2
• Failing to consider non-hematologic causes of easy bruising, such as connective tissue disorders, medication effects, and non-accidental trauma 1, 7
• Not obtaining a thorough bleeding history using a structured assessment tool 1
• Overlooking the need for specific VWD testing in patients with mucocutaneous bleeding despite normal PT/aPTT 1, 3
• Not recognizing that normal coagulation studies (INR, PTT) and von Willebrand parameters do not rule out all bleeding disorders, as some disorders may have variable expression 6, 8

Interpretation of Results

• Normal PT and aPTT with abnormal bleeding suggest a platelet disorder, most commonly von Willebrand disease 2
• Normal PT with prolonged aPTT indicates a deficit in the intrinsic pathway, requiring a mixing study 2
• Prolonged PT with normal aPTT warrants a vitamin K challenge 2
• Prolonged PT and aPTT suggest liver failure or multiple factor deficiencies 2

If initial testing does not reveal an etiology in a patient with high suspicion for a bleeding disorder, referral to a hematologist is warranted for additional evaluation 2.