What is the initial step in the workup of a patient presenting with eosinophilia?

Initial Workup of Eosinophilia

The initial step in the workup of a patient presenting with eosinophilia should include a thorough history focusing on travel, new medications, and symptoms of organ involvement, followed by targeted laboratory testing based on clinical presentation. 1

Understanding Eosinophilia

Eosinophilia is defined as a peripheral blood eosinophil count >0.5 × 10⁹/L 1. The severity can be classified as:

• Mild: 0.5-1.5 × 10⁹/L
• Moderate: 1.5-5.0 × 10⁹/L
• Severe: >5.0 × 10⁹/L

Initial Diagnostic Approach

Step 1: Focused History

• Travel history: Particularly to areas endemic for helminth infections 1
• Medication history: Focus on NSAIDs, beta-lactam antibiotics, and other common culprits 1
• Allergy/atopy history: Asthma, eczema, hay fever 1
• Symptom assessment: Evaluate for organ-specific symptoms that might indicate end-organ damage 1

Step 2: Laboratory Testing

The initial laboratory workup should include:

• Complete blood count with differential to confirm eosinophilia 1
• Comprehensive metabolic panel with uric acid, lactate dehydrogenase, and liver function tests 1
• Serum tryptase levels and vitamin B12 levels (elevated in myeloproliferative variants) 1
• Peripheral blood smear review for evidence of other blood count abnormalities 1

Step 3: Additional Testing Based on Clinical Context

For returning travelers or migrants:

• Parasite serology (particularly for Strongyloides) 1
• Stool examination for ova and parasites 1

For patients with persistent eosinophilia (≥1.5 × 10⁹/L for >3 months):

• Bone marrow aspirate and biopsy with immunohistochemistry 1
• Cytogenetic studies including FISH and/or RT-PCR to detect TK fusion gene rearrangements 1

Common Causes to Consider

1. Infectious causes: Helminth infections are the most common identifiable cause in returning travelers (19-80% of cases) 1
2. Allergic/atopic conditions: Common in countries with low rates of endemic helminth infections 1
3. Medication reactions: NSAIDs, beta-lactams, nitrofurantoin 1
4. Hematologic malignancies: Particularly myeloproliferative neoplasms 1
5. Autoimmune/connective tissue disorders: Less common but important to consider 1

Special Considerations

For Travelers/Migrants

Helminth infections are particularly important to exclude as they can cause long-term health problems. For example:

• Strongyloides stercoralis can persist lifelong and cause hyperinfection syndrome in immunocompromised patients 1
• Schistosoma haematobium is associated with bladder carcinoma 1

For Persistent Eosinophilia

Patients with eosinophilia ≥1.5 × 10⁹/L for more than 3 months require referral to a hematologist once infectious causes have been excluded or treated 1.

For High-Grade Eosinophilia

Any patient with evidence of end-organ damage needs urgent medical assessment and consideration of emergency treatment 1.

Common Pitfalls to Avoid

1. Failing to consider geographic exposure: Travel or residence history is crucial for identifying potential parasitic causes 1

2. Overlooking medication causes: Always review all medications, including over-the-counter drugs 1

3. Inadequate follow-up: Eosinophilia may be transient during tissue migration phases of parasitic infections, so negative initial tests don't rule out infection 1

4. Missing clonal disorders: In patients with persistent unexplained eosinophilia, next-generation sequencing and bone marrow evaluation are essential to exclude myeloid neoplasms 1

5. Neglecting end-organ damage assessment: Persistent eosinophilia can itself cause significant organ damage, particularly to the heart, lungs, and central nervous system 1