What causes bruising?

Causes of Bruising

Bruising is most commonly caused by trauma or injury, but can also result from bleeding disorders, certain medical conditions, medications, or non-accidental trauma in vulnerable populations. 1, 2

Common Causes of Bruising

Traumatic Causes

• Normal accidental trauma (most common cause)
• Non-accidental trauma/abuse (especially concerning when bruises appear in unusual locations like ears, neck, torso, buttocks, or genitals) 1, 2
• Patterned bruising suggesting implements or squeezing 2

Medical Conditions

1. Bleeding Disorders:

   • Von Willebrand disease (most common inherited bleeding disorder) 2, 3
   • Hemophilia (factor VIII or IX deficiency) 1, 2
   • Factor XIII deficiency 1
   • Platelet function disorders 1, 2
   • Fibrinolytic defects (rare) 1

2. Other Medical Conditions:

   • Ehlers-Danlos syndrome (connective tissue disorder) 1, 2
   • Scurvy (vitamin C deficiency) 1, 2
   • Cancer and infiltrative disorders 1, 2
   • Vitamin K deficiency (especially in infants) 1
   • Liver disease 3

3. Medication-Related Causes:

   • Anticoagulants (warfarin, heparin, DOACs)
   • Antiplatelet medications (aspirin, clopidogrel)
   • Certain antibiotics
   • NSAIDs 3, 4

Evaluation of Bruising

Key History Elements

• Pattern and location of bruising
• Timing and onset of bruises
• Family history of bleeding disorders
• Medication review
• History of excessive bleeding after procedures (circumcision, dental work, surgery) 1, 3
• In children: developmental stage and mobility 1

Physical Examination Findings

• Mucocutaneous bleeding: Suggests platelet dysfunction 3
• Hemarthroses or hematomas: More common in coagulopathy 3
• Bruising in unusual locations: May indicate non-accidental trauma, especially in non-mobile children 1, 2
• Multiple bruises in different stages of healing: May suggest ongoing trauma 2

Laboratory Evaluation

1. Initial screening tests:

   • Complete blood count (CBC) with platelet count
   • Peripheral blood smear
   • Prothrombin time (PT)
   • Activated partial thromboplastin time (aPTT) 3, 4

2. Interpretation of results:

   • Normal PT and aPTT: May indicate platelet disorder (e.g., von Willebrand disease) 3, 4
   • Normal PT, prolonged aPTT: Suggests intrinsic pathway deficit (requires mixing study) 3, 4
   • Prolonged PT, normal aPTT: Consider vitamin K deficiency or extrinsic pathway disorder 4
   • Prolonged PT and aPTT: Consider liver disease or multiple factor deficiencies 3

3. Additional testing when indicated:

   • Von Willebrand factor antigen and ristocetin cofactor activity tests 2
   • Platelet aggregation studies or PFA-100 1, 2
   • Factor assays 1
   • Fibrinogen level 1

Important Clinical Considerations

• Mild factor deficiencies can cause significant bruising despite minimal laboratory abnormalities 1, 2
• In children with unexplained bruising, consider both bleeding disorders and non-accidental trauma 1, 5
• The "easy bruising syndrome" can occur in patients (predominantly women) with normal platelet counts and coagulation profiles 6
• Hematology consultation is warranted when initial evaluation suggests a bleeding disorder or when suspicion remains high despite normal laboratory results 2, 4

Red Flags Requiring Urgent Evaluation

• Bruising in non-mobile infants
• Bruising in unusual locations (ears, buttocks, genitals)
• Patterned bruising
• Bruising accompanied by other concerning symptoms (headache, abdominal pain)
• Family history of bleeding disorders with new or worsening bruising 1, 2