What workup is needed for a patient with spontaneous bruising after minor trauma, such as scratching a mosquito bite?

Workup for Spontaneous Bruising After Minor Trauma

A patient with spontaneous bruising after scratching a mosquito bite should undergo a focused hematologic workup including complete blood count with platelet count, prothrombin time, partial thromboplastin time, and bleeding time to rule out underlying bleeding disorders.

Initial Assessment

When evaluating a patient with spontaneous bruising after minor trauma such as scratching a mosquito bite, it's essential to determine whether the bruising is proportional to the trauma or suggests an underlying bleeding disorder. This distinction is critical for proper diagnosis and management.

Key History Elements to Obtain:

• Pattern and frequency of bruising
• Relation to trauma (spontaneous vs. post-traumatic)
• Family history of bleeding disorders
• Medication use (particularly anticoagulants, antiplatelets, SSRIs)
• Bleeding from other sites (gums, nose, menstrual bleeding)
• Previous surgical or dental procedures with abnormal bleeding

Laboratory Evaluation

The initial screening tests should include:

1. Complete blood count (CBC) with platelet count - to assess for thrombocytopenia
2. Prothrombin time (PT) - evaluates the extrinsic pathway
3. Partial thromboplastin time (PTT) - evaluates the intrinsic pathway
4. Bleeding time - assesses platelet function

These screening tests are adequate to rule out significant bleeding problems in most patients 1. Abnormal results in these initial tests would indicate the need for more specialized testing.

Extended Testing (if indicated)

If initial screening tests are abnormal or if there is a strong personal or family history of abnormal bleeding despite normal screening tests:

• von Willebrand factor antigen and activity - to rule out von Willebrand disease
• Platelet aggregation studies - to assess platelet function disorders
• Factor assays - particularly for factors VIII, IX, and XI

Special Considerations

Medication-Induced Bruising

Certain medications can cause or exacerbate bruising tendencies:

• SSRIs like fluoxetine can cause bruising by preventing serotonin-induced amplification of platelet aggregation 2
• Antiplatelet medications (aspirin, clopidogrel)
• Anticoagulants (warfarin, DOACs)

Child Abuse Considerations

In pediatric cases, it's important to consider both bleeding disorders and non-accidental injury as potential causes of bruising:

• Bleeding disorders and non-accidental injury are not mutually exclusive 3
• In one study, 16% of children with suspected non-accidental injury had abnormal initial coagulation test results 3
• The evaluation for bleeding disorders in children with suspected abuse should be guided by clinical presentation and laboratory findings 4

Algorithm for Management

1. Initial screening tests: CBC with platelet count, PT, PTT, bleeding time
2. If normal results but strong clinical suspicion of bleeding disorder:
   • Consider specialized testing for von Willebrand disease and platelet function disorders
   • Review medications that may affect coagulation
3. If abnormal results:
   • Refer to hematology for comprehensive evaluation
   • Consider mixing studies to differentiate factor deficiencies from inhibitors

Pitfalls to Avoid

• Do not rule out bleeding disorders solely based on patient and family history 4
• Do not assume that the presence of a bleeding disorder excludes the possibility of trauma or abuse 3
• Do not overlook medication-induced causes of increased bruising tendency 2

In cases where initial screening tests are normal but clinical suspicion remains high, referral to a specialized hemostasis center may be necessary for more extensive and repeated investigation 1.