What labs are included in the initial workup for a patient presenting with eosinophilia?

Initial Workup for Eosinophilia

The initial laboratory workup for a patient presenting with eosinophilia should include complete blood count with differential, peripheral blood smear, comprehensive metabolic panel with liver function tests, urinalysis with protein-to-creatinine ratio, C-reactive protein, serum tryptase, and vitamin B12 levels. 1

Definition and Classification

• Eosinophilia is defined as a peripheral blood eosinophil count >0.5 × 10⁹/L
• Severity classification:
  • Mild: >0.5 × 10⁹/L
  • Moderate: >1.5 × 10⁹/L
  • Severe: >5.0 × 10⁹/L 1

Initial Laboratory Workup

1. Complete blood count with differential

   • Confirms eosinophilia
   • Determines absolute eosinophil count (AEC)
   • Assesses for other hematologic abnormalities

2. Peripheral blood smear

   • Evaluates blood cell morphology
   • Helps identify potential hematologic malignancies

3. Comprehensive metabolic panel with liver function tests

   • Assesses organ function
   • Identifies potential end-organ damage

4. Urinalysis with protein-to-creatinine ratio

   • Evaluates kidney function
   • Screens for renal involvement

5. C-reactive protein

   • Assesses inflammation
   • Helps differentiate between inflammatory and non-inflammatory causes

6. Serum tryptase

   • Evaluates mast cell activation
   • Helps rule out mast cell disorders

7. Vitamin B12 levels

   • Assesses nutritional status
   • May be elevated in certain myeloproliferative disorders 1

Additional Diagnostic Considerations

Travel and Exposure History

For patients with travel history to tropical/subtropical regions, additional tests should include:

• Concentrated stool microscopy (three samples)
• Serological tests for parasitic infections based on geographical exposure:
  • Schistosomiasis (Africa, parts of Asia, South America)
  • Strongyloidiasis (worldwide, especially tropics)
  • Filariasis (tropical regions)
  • Other helminth infections 2, 1

Medication Review

• Complete medication history to identify potential drug-induced eosinophilia
• Consider withdrawal of suspected medications 1

Further Investigation

Further investigation is warranted if:

• Eosinophilia persists >3 months
• Eosinophil count exceeds 1.5 × 10⁹/L
• Associated symptoms develop
• Evidence of end-organ damage 1

Common Pitfalls to Avoid

1. Failing to calculate the absolute eosinophil count

   • Always calculate AEC by multiplying the percentage of eosinophils by the total white blood cell count 3

2. Attributing hypereosinophilia (≥1500 eosinophils/μL) to allergy alone

   • Hypereosinophilia is rarely, if ever, explained by allergy alone and should always prompt further workup 3

3. Overlooking transient eosinophilia

   • Transient eosinophilia may disappear days later and is commonly associated with tissue migration phase of parasitic infections, allergic reactions, or medication effects 1

4. Missing the timing of serological tests

   • Most serological tests for parasitic infections do not become positive until 4-12 weeks after infection 2

5. Neglecting to repeat stool examinations

   • All patients returning from the tropics with eosinophilia should be investigated with concentrated stool microscopy, and multiple samples increase diagnostic yield 2

By following this systematic approach to the initial workup of eosinophilia, clinicians can efficiently identify the underlying cause and implement appropriate treatment to prevent potential end-organ damage.