How should a patient with elevated eosinophil count be evaluated and treated?

Evaluation and Management of Elevated Eosinophil Count

A patient with elevated eosinophil count should undergo a systematic diagnostic workup starting with confirmation of absolute eosinophil count, detailed history focusing on allergies, medications, and travel, followed by targeted testing based on suspected etiology, with treatment directed at the underlying cause. 1

Understanding the Patient's Eosinophilia

The patient's lab results show:

• Eosinophil percentage: 7.0% (HIGH)
• Absolute eosinophil count: 0.57 × 10³/μL (HIGH)
• Basophil percentage: 1.1% (HIGH)

This represents mild eosinophilia, defined as an absolute eosinophil count >0.5 × 10⁹/L 1, 2. The elevated basophil count may also suggest an allergic or inflammatory process.

Diagnostic Approach

Step 1: Confirm and Classify Eosinophilia

• Absolute eosinophil count of 0.57 × 10³/μL confirms mild eosinophilia 1
• Severity classification:
  • Mild: >0.5 × 10⁹/L
  • Moderate: >1.5 × 10⁹/L
  • Severe: >5.0 × 10⁹/L 1

Step 2: Detailed Clinical History

Focus on:

• Medication history (current and recent medications)
• Allergy history
• Travel to tropical/subtropical regions
• Exposure to freshwater
• Consumption of raw foods
• Walking barefoot in endemic areas
• Symptoms of organ involvement 1, 2

Step 3: Initial Laboratory Workup

• Complete blood count with differential (already done)
• Peripheral blood smear to evaluate blood cell morphology
• Comprehensive metabolic panel with liver function tests
• Urinalysis with protein-to-creatinine ratio
• C-reactive protein
• Serum tryptase
• Vitamin B12 levels 1

Step 4: Additional Testing Based on Clinical Suspicion

For suspected parasitic infection:

• Concentrated stool microscopy (multiple samples increase yield)
• Serological tests for parasitic infections based on geographical exposure
• Note: Most serological tests become positive 4-12 weeks after infection 1

For suspected allergic disorders:

• Allergy testing (skin prick testing or specific IgE)
• Evaluation for eosinophilic esophagitis if GI symptoms present 3, 1

For persistent unexplained eosinophilia:

• Consider bone marrow examination
• Flow cytometry
• Genetic testing for PDGFRA, PDGFRB, or FGFR1 rearrangements 1, 4

Treatment Approach

Treatment should target the underlying cause:

For Parasitic Infections:

• Hookworm: Albendazole 400 mg daily for 3 days
• Schistosomiasis: Praziquantel 40 mg/kg twice daily for 5 days
• Strongyloides: Ivermectin 200 μg/kg/day for 1-2 days
• Filariasis: Diethylcarbamazine (specialist consultation)
• Cutaneous larva migrans: Ivermectin (200 μg/kg single dose) or Albendazole (400 mg/day for 3 days) 1

For Drug-Induced Eosinophilia:

• Immediate withdrawal of the causative medication 1

For Eosinophilic Esophagitis:

• Topical steroids as first-line treatment
• Proton pump inhibitors
• Consider dietary modifications
• Endoscopic dilatation for strictures 1

For Idiopathic Hypereosinophilic Syndrome:

• Corticosteroids as first-line therapy
• Hydroxyurea and interferon-α for steroid-refractory cases
• Mepolizumab (IL-5 antagonist) for idiopathic HES 1, 4

Follow-Up and Monitoring

• Regular monitoring of blood counts to confirm resolution 1
• For mild and transient eosinophilia, follow-up with complete blood counts 1
• For persistent eosinophilia, regular monitoring for end-organ damage 1
• Prompt diagnosis and treatment to prevent irreversible organ damage, particularly cardiac complications 1

Important Caveats

• Hypereosinophilia (>1.5 × 10⁹/L) is rarely explained by allergy alone and should always prompt further workup 1, 2
• Further investigation is warranted if eosinophilia persists >3 months, eosinophil count exceeds 1.5 × 10⁹/L, associated symptoms develop, or evidence of end-organ damage appears 1
• Transient eosinophilia may be associated with the tissue migration phase of parasitic infections, allergic reactions, or medication effects 1
• Only tissue-invasive helminthic parasites cause eosinophilia, which limits its general application as a screening tool for all parasitic infections 5

This systematic approach will help identify the underlying cause of the patient's eosinophilia and guide appropriate treatment to prevent potential complications.