How should I evaluate and manage a 64-year-old woman with a mild eosinophilia (eosinophil count 1080 cells/µL) and a total white‑blood‑cell count of 11.8 × 10⁹/L?

Evaluation and Management of Eosinophilia (1080 cells/µL)

This 64-year-old woman has mild eosinophilia (1.08 × 10⁹/L) that requires systematic evaluation to identify the underlying cause, with particular attention to travel history, medication use, and atopic conditions, as these account for the vast majority of cases in this range.

Immediate Assessment

The eosinophil count of 1.08 × 10⁹/L falls into the mild eosinophilia category (defined as >0.5 × 10⁹/L but <1.5 × 10⁹/L) 1. This level does not require urgent intervention unless there are signs of end-organ damage affecting the heart, lungs, or central nervous system 1.

Critical First Steps:

• Assess for end-organ damage: Check for cardiac symptoms (chest pain, dyspnea), pulmonary symptoms (cough, shortness of breath), or neurological symptoms (confusion, focal deficits). If present, urgent medical assessment is needed 1
• No immediate haematology referral needed: Referral to haematology is only indicated if eosinophilia ≥1.5 × 10⁹/L persists for >3 months after infectious causes are excluded 1

Diagnostic Algorithm

1. Detailed History (Most Critical)

Focus on these specific elements:

• Travel and residence history: Any travel to or residence in endemic areas, particularly West Africa (for filariasis), tropical regions (for helminth infections) 1
• Medication review: All current and recent medications, as drugs are among the commonest non-infectious causes 1
• Atopic history: Asthma, eczema, hay fever—the most common causes in low-endemic countries 1, 2
• Gastrointestinal symptoms: Diarrhea, abdominal pain (parasitic infections)
• Respiratory symptoms: Wheezing, cough (ABPA, eosinophilic pneumonia)
• Skin manifestations: Rashes, urticaria

2. First-Line Laboratory Investigations

Based on the 2025 UK guidelines 1:

For patients with travel/residence history:

• Stool microscopy (×3 samples on separate days) for ova, cysts, and parasites
• Helminth serology: Strongyloides, Schistosoma, Filaria (only if West Africa exposure)
• Serum IgE: If ≥1000 IU/L, strongly suggests fungal allergy or parasitic infection 3

For all patients:

• Complete blood count with differential: Confirm eosinophil count, assess for other cytopenias
• Comprehensive metabolic panel: Assess organ function
• Serum tryptase: Elevated in 14.5% of eosinophilia cases across diagnostic groups 3

3. Diagnostic Probability by Category

In secondary care settings, the most common causes are 2, 3:

1. Atopic diseases (38-53%): Asthma, eczema, allergic rhinitis
2. Fungal allergy (21%): Particularly ABPA
3. Parasitic infections (16%): Strongyloides, Schistosoma, hookworm
4. Severe eosinophilic asthma (13%)
5. Drug reactions: NSAIDs, antibiotics, others
6. Hypereosinophilic syndrome/EGPA (20% combined): Less common at this eosinophil level

Management Strategy

If Travel/Migration History Present:

Empirical treatment may be considered for asymptomatic patients with travel history to endemic areas while awaiting test results 1. The specific regimen depends on geographic exposure and should target likely helminth infections.

Critical caveat: Strongyloides stercoralis requires specific attention as it can persist lifelong and cause fatal hyperinfection syndrome in immunocompromised patients 1.

If No Travel History:

1. Review and discontinue potential causative medications
2. Optimize management of atopic conditions if present
3. Consider specialist referral based on clinical presentation:
   • Pulmonology: If respiratory symptoms or infiltrates
   • Gastroenterology: If GI symptoms
   • Dermatology: If significant skin involvement
   • Allergy/Immunology: For comprehensive evaluation

Follow-Up Protocol:

• Repeat eosinophil count in 4-6 weeks to assess persistence
• If persistently elevated (≥1.5 × 10⁹/L for >3 months) after excluding/treating infectious causes: Refer to haematology for evaluation of primary eosinophilic disorders including bone marrow examination, cytogenetics, and molecular testing for tyrosine kinase gene fusions 4
• If remains <1.5 × 10⁹/L: Continue monitoring and treat underlying cause

Common Pitfalls to Avoid:

• Don't assume all eosinophilia is benign: Even mild persistent eosinophilia can cause end-organ damage over time 1
• Don't rely on single stool sample: Sensitivity is low; require 3 separate samples 1
• Don't overlook medication causes: Carefully review all medications including over-the-counter and supplements
• Don't forget Strongyloides: This requires specific testing and treatment due to risk of fatal hyperinfection 1
• Don't order day/night blood samples for filariasis: Updated 2025 guidelines recommend serology as sole first-line test 1