What are the causes of an elevated white blood cell count of 11.8 × 10⁹/L with eosinophilia in a 64‑year‑old woman?

Elevated WBC and Eosinophilia in a 64-Year-Old Woman

In a 64-year-old woman with a WBC of 11.8 × 10⁹/L and elevated eosinophils, the most likely causes are allergic conditions (asthma, eczema, drug reactions), parasitic infections (particularly if there is travel history), or medications—these account for approximately 80% of eosinophilia cases. 1

Understanding the Laboratory Values

The WBC of 11.8 × 10⁹/L is mildly elevated but falls within the normal range for hospitalized patients (reference range 1.6-14.5 × 10⁹/L) 2. The critical question is the absolute eosinophil count (AEC), which determines the diagnostic approach:

• Eosinophilia: AEC >0.5 × 10⁹/L
• Hypereosinophilia: AEC ≥1.5 × 10⁹/L 1, 3

This distinction is crucial because hypereosinophilia (≥1.5 × 10⁹/L) is rarely explained by allergy alone and mandates comprehensive workup 3.

Most Common Causes (in Order of Frequency)

1. Allergic/Atopic Conditions (~80% of cases)

• Allergic asthma, atopic dermatitis, eczema, hay fever
• Drug reactions (review ALL medications)
• These are the dominant causes in countries with low endemic helminth infections 1, 4

2. Parasitic Infections (Second Most Common)

Strongyloides stercoralis is the most important parasitic cause, particularly because:

• It can persist lifelong
• Can cause fatal hyperinfection syndrome if the patient becomes immunocompromised 1
• Other helminths (worms) account for 19-80% of eosinophilia in travelers/migrants 1

Key travel history questions:

• Any travel to endemic areas (tropical/subtropical regions)?
• West Africa exposure (for filarial infections)? 1
• Immigration history?

3. Medications

Review all current and recent medications—drug-induced eosinophilia is extremely common 1

4. Less Common but Serious Causes

Hematologic malignancies (rare but critical to exclude):

• Myeloproliferative neoplasms with eosinophilia
• Lymphomas (Hodgkin, T-cell lymphomas)
• Only 2% of eosinophilia cases in one large series were myeloproliferative disease 5

Other conditions:

• Systemic vasculitis (eosinophilic granulomatosis with polyangiitis/Churg-Strauss)
• Solid tumors (usually advanced stage)
• Autoimmune/inflammatory disorders 4

Diagnostic Approach

Immediate Assessment

1. Calculate the absolute eosinophil count (percentage × total WBC)

2. Screen for end-organ damage (this is life-threatening):

   • Cardiac: Troponin, NT-proBNP, ECG, echocardiogram (endomyocardial fibrosis is the most dangerous complication) 4
   • Pulmonary: Chest imaging, pulmonary function if symptomatic
   • Neurological: Any focal deficits, confusion, seizures
   • Dermatologic: Rashes, urticaria
   • Gastrointestinal: Diarrhea, abdominal pain

If end-organ damage is present, this is a medical emergency requiring urgent specialist consultation 1.

First-Line Investigations

For mild eosinophilia (<1.5 × 10⁹/L):

• Detailed medication review (stop any non-essential drugs)
• Assess for allergic conditions (asthma, eczema, rhinitis)
• Travel history (if positive, helminth serology) 1
• Repeat CBC in 1 month to confirm persistence

For hypereosinophilia (≥1.5 × 10⁹/L):

• Parasitic workup: Stool ova and parasites (×3), Strongyloides serology, schistosomiasis serology if travel history 1
• Serum IgE: If ≥1000 IU/L, 91% have fungal allergy or parasitic infection 5
• Serum tryptase: Elevated in 14.5% of eosinophilia cases (suggests myeloproliferative disease if markedly elevated) 5
• Peripheral blood smear: Look for dysplasia, immature cells, blasts
• Flow cytometry with T-cell immunophenotyping: To detect aberrant T-cell clones (lymphocyte-variant HES) 4

Second-Line/Specialist Investigations

If hypereosinophilia persists >3 months without identified cause:

• Bone marrow biopsy with cytogenetics and molecular testing for PDGFRA, PDGFRB, FGFR1 rearrangements 4, 6
• Refer to hematology once infectious causes excluded or treated 1

Critical Pitfalls to Avoid

1. Missing Strongyloides: Always test for this if any travel history—it can be fatal with immunosuppression 1

2. Assuming allergy explains hypereosinophilia: Allergy rarely causes AEC ≥1.5 × 10⁹/L alone 3

3. Delaying cardiac evaluation: Eosinophil-mediated cardiac damage is the most life-threatening complication and can occur at any eosinophil level 1, 4

4. Not repeating the count: Single elevated values may be transient; persistence (>1 month) is required for diagnosis 1

5. Overlooking medications: This is one of the most common and reversible causes 1

Age and Comorbidity Considerations

In this 64-year-old patient, consider:

• Diabetes and obesity are associated with higher baseline eosinophil counts 7
• Solid tumors with eosinophilia typically occur in advanced disease 4
• Myeloproliferative disorders increase with age but remain rare 5

When to Refer

Urgent hematology referral if:

• Hypereosinophilia (≥1.5 × 10⁹/L) persisting >3 months after excluding/treating infections 1
• Any evidence of end-organ damage 1
• Elevated serum tryptase, abnormal peripheral smear, or suspected clonal disorder 5

Infectious disease referral if:

• Travel history with suspected parasitic infection 1, 4