What lab tests are indicated for a patient with increased bruising?

Laboratory Workup for Increased Bruising

Order a complete blood count (CBC) with peripheral smear, PT/INR, and aPTT as your initial laboratory panel for any patient presenting with increased bruising. 1

Initial First-Line Laboratory Tests

The following tests should be ordered together as your baseline evaluation:

• CBC with platelet count and peripheral blood smear to identify thrombocytopenia, abnormal platelet morphology, or signs of bone marrow disorders 1
• PT/INR to assess the extrinsic coagulation pathway and screen for factor VII deficiency, vitamin K deficiency, or liver disease 1
• aPTT to evaluate the intrinsic coagulation pathway and detect deficiencies in factors VIII, IX, XI, or XII 1
• Fibrinogen level to screen for fibrinogen disorders 1

These basic tests can identify thrombocytopenia, coagulation factor deficiencies, or suggest other bleeding disorders, but they will not detect von Willebrand disease or mild platelet function disorders 1. This is a critical pitfall to avoid.

When to Add Von Willebrand Disease Testing

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

The three essential VWD tests to order together are:

• VWF antigen (VWF:Ag) - measures the quantity of von Willebrand factor protein 2, 3
• VWF ristocetin cofactor activity (VWF:RCo) - assesses functional ability of VWF to bind platelets 2, 3
• Factor VIII coagulant activity (FVIII) - evaluates factor VIII levels, which are protected by VWF 2, 3

All three tests must be ordered together because they establish not only the diagnosis but also suggest the type and severity of VWD 2, 3. A VWF:RCo to VWF:Ag ratio below 0.5-0.7 indicates abnormal VWF function and warrants specialized testing 2.

Special Considerations for Pediatric Patients

In children with easy bruising, expand your workup to include:

• Serum calcium, phosphorus, and alkaline phosphatase to screen for bone metabolism disorders 1
• Parathyroid hormone and 25-hydroxy-vitamin D for metabolic bone disease 1
• Serum copper and ceruloplasmin to evaluate for copper deficiency 1

Critical Pitfalls to Avoid

• Do not rely solely on PT and aPTT to rule out bleeding disorders - this approach will miss von Willebrand disease and mild platelet function disorders, which are among the most common inherited bleeding disorders 1
• Do not order VWF multimer analysis as part of initial screening - this complex test should only be performed if initial VWD testing shows abnormalities (low VWF levels or abnormal VWF:RCo/VWF:Ag ratio) 2, 3
• Consider non-hematologic causes including connective tissue disorders (Ehlers-Danlos syndrome), medication effects (aspirin, NSAIDs, anticoagulants), vitamin C deficiency, and non-accidental trauma 1
• Timing matters - VWF levels can be falsely elevated by stress, inflammation, pregnancy, or estrogen therapy, and are naturally 25% lower in blood type O individuals 3

Algorithm for Interpretation

If PT and aPTT are both normal but bruising persists with mucocutaneous bleeding:

• Order the three VWD tests (VWF:Ag, VWF:RCo, FVIII) 2, 1
• Consider platelet function testing if VWD testing is normal 4

If aPTT is prolonged but PT is normal:

• Perform mixing study to distinguish factor deficiency from inhibitor 5
• Check factors VIII, IX, and XI levels 5

If PT is prolonged but aPTT is normal:

• Consider vitamin K deficiency or factor VII deficiency 5
• Evaluate for liver disease 5

If both PT and aPTT are prolonged:

• Evaluate for liver failure, disseminated intravascular coagulation, or multiple factor deficiencies 5

When to Refer to Hematology

Refer to a hematology specialist if:

• Initial testing reveals abnormal VWD parameters requiring specialized assays 3
• Normal screening tests but high clinical suspicion for bleeding disorder persists 4, 5
• Abnormal results require interpretation of complex patterns or genetic testing 4