In a 10‑year‑old child with an otherwise normal complete blood count but elevated absolute eosinophil count and absolute basophil count, what are the most likely etiologies and the recommended initial evaluation and management?

Elevated Eosinophils and Basophils in a 10-Year-Old Child

In a 10-year-old child with isolated elevation of absolute eosinophil and basophil counts, allergic disorders are by far the most likely etiology (accounting for 80% of pediatric eosinophilia cases), and your initial evaluation should focus on identifying atopic conditions—particularly asthma, allergic rhinitis, atopic dermatitis, and food allergies—while simultaneously ruling out parasitic infections if there is any travel or exposure history. 1

Understanding the Clinical Context

The simultaneous elevation of both eosinophils and basophils in a child with otherwise normal labs strongly suggests a type 2 inflammatory process, most commonly driven by allergic disease. 2, 1

Most Likely Etiologies by Frequency

Allergic disorders dominate the differential diagnosis:

• Allergic diseases account for 80% of all pediatric eosinophilia cases, with the majority presenting as mild eosinophilia (0.5-1.5 × 10⁹/L). 1
• In atopic children, 20-100% demonstrate elevated peripheral eosinophil counts, though elevations are typically modest (2-fold increase). 3
• 50-80% of children with allergies are atopic based on coexistence of atopic dermatitis, allergic rhinitis, and/or asthma. 3

Food allergy and primary immunodeficiency emerge as independent risk factors:

• Multiple logistic regression analysis identified food allergy (OR: 1.866) and primary immunodeficiencies (OR: 2.200) as independent factors for childhood eosinophilia. 1

Initial Evaluation Algorithm

Step 1: Detailed Clinical History (Focus on Specific Red Flags)

Atopic symptom assessment:

• Document presence of asthma symptoms (wheezing, chronic cough, exercise intolerance), allergic rhinitis (nasal congestion, sneezing, rhinorrhea), atopic dermatitis (eczematous rash, pruritus), and food allergies (urticaria, angioedema, gastrointestinal symptoms after specific foods). 2, 3
• Gastrointestinal symptoms such as dysphagia or food impaction warrant consideration of eosinophilic esophagitis, though peripheral eosinophilia occurs in only 10-50% of adults and 20-100% of children with this condition. 2, 3

Travel and exposure history:

• Obtain detailed travel history focusing on fresh water exposure in Africa/tropical regions, raw/undercooked meat consumption, as helminth infections account for 19-80% of cases in returning travelers or migrants. 2
• Even without travel history, consider parasitic infections in endemic-exposed populations or those with pica behavior. 2

Family history:

• Document family history of atopy and consanguinity, as primary immunodeficiencies are not rare causes of eosinophilia, especially in regions where consanguineous marriages are common. 1

Step 2: Severity Classification and Risk Stratification

Classify the eosinophilia level:

• Mild eosinophilia (0.5-1.5 × 10⁹/L) is most commonly caused by allergic disorders or medications in non-endemic areas. 2
• Moderate eosinophilia (1.5-5.0 × 10⁹/L) requires more extensive evaluation if persistent. 4
• Severe eosinophilia (≥5.0 × 10⁹/L) demands urgent evaluation for primary immunodeficiencies, malignancies, or hypereosinophilic syndrome. 1

Assess for end-organ damage (critical in moderate-to-severe cases):

• Any patient with eosinophilia presenting with symptoms suggesting end-organ damage needs urgent medical evaluation—specifically cardiac involvement (chest pain, dyspnea, heart failure symptoms), pulmonary involvement (persistent cough, wheezing, infiltrates), or neurological involvement (altered mental status, focal deficits, peripheral neuropathy). 2

Step 3: Initial Laboratory Workup

For all children with persistent eosinophilia:

• Repeat complete blood count to confirm persistence and document absolute eosinophil count (not just percentage). 2, 3
• Total serum IgE level: A level >150 U/ml is strongly suggestive of atopic disease in 3-year-olds, though this threshold may vary by age. 5
• Aeroallergen sensitivity testing (skin-prick or specific IgE assays) to identify trigger allergens, as 50-80% of eosinophilic patients have concurrent atopic conditions. 2

Parasitic evaluation (essential even in mild cases with any exposure risk):

• Stool microscopy for ova and parasites (3 separate concentrated specimens). 2
• Strongyloides serology and culture immediately, as this parasite can persist lifelong and cause fatal hyperinfection syndrome in immunocompromised patients. 2
• Schistosomiasis serology if fresh water exposure in endemic areas. 2

Step 4: Symptom-Directed Investigations

If gastrointestinal symptoms present:

• Upper endoscopy with multiple biopsies (minimum 6 biopsies: 2-3 from proximal and 2-3 from distal esophagus) to evaluate for eosinophilic esophagitis, as peripheral eosinophil counts do not reliably correlate with tissue eosinophilia. 2, 3

If respiratory symptoms present:

• Pulmonary function tests and fractional exhaled nitric oxide (FeNO) measurements serve as surrogate markers for eosinophilic airway inflammation. 6
• Sputum eosinophil counts (if available in specialist settings) provide compelling evidence of beneficial response to corticosteroid therapy. 6

If severe eosinophilia (≥5.0 × 10⁹/L) or concerning features:

• Bone marrow examination with cytogenetics and molecular testing for PDGFRA/PDGFRB rearrangements to exclude clonal eosinophilia or myeloproliferative disorders. 7
• Immunodeficiency workup including immunoglobulin levels, lymphocyte subsets, and functional assays, as primary immunodeficiencies were the most common etiology in the severe eosinophilia group. 1

Management Approach

For Allergic Disease (Most Likely Scenario)

Initial management targets the underlying atopic condition:

• Corticosteroid therapy (topical, inhaled, or systemic depending on manifestation) decreases eosinophil counts 2- to 7-fold, with effects potentially visible as early as 6 hours. 6
• Management strategies targeting eosinophil normalization in asthma reduce severe exacerbations by up to 60%. 6
• In eosinophilic esophagitis, topical swallowed corticosteroids (fluticasone or budesonide) decrease blood eosinophil counts in 88% of patients. 2, 3

For Parasitic Infections (If Identified)

Empiric treatment may be warranted in endemic-exposed patients:

• Ivermectin 200 μg/kg daily for 2 days for Strongyloidiasis. 2
• Albendazole 400 mg twice daily for 3 days for Loeffler's syndrome (Ascaris, hookworm). 2
• Praziquantel 40 mg/kg as a single dose for Schistosomiasis, repeated at 6-8 weeks. 2

Critical warning: Do not use diethylcarbamazine (DEC) if Loa loa microfilariae are seen in blood, as it may cause fatal encephalopathy; use corticosteroids with albendazole first to reduce microfilarial load. 2

Monitoring and Follow-Up

For persistent eosinophilia without identified cause:

• Moderate to severe eosinophilia (≥1.5 × 10⁹/L) requires referral to hematology if it persists for more than 3 months after infectious causes have been excluded or treated. 2
• Regular clinic visits to assess for development of symptoms or end-organ damage. 2
• Repeat laboratory testing at 4-week intervals to document persistence, as hypereosinophilia is defined by eosinophil count >1.5 × 10⁹/L in at least two consecutive tests with a minimum 4-week interval. 4

Critical Pitfalls to Avoid

Do not assume eosinophilia alone is adequate screening for helminth infection, as many infected patients have normal eosinophil counts, and only tissue-invasive helminthic parasites cause eosinophilia. 2

Do not rely solely on peripheral eosinophil counts to assess tissue eosinophilia in conditions like eosinophilic esophagitis, as tissue biopsy is the gold standard. 2, 3

Do not wait for symptoms to develop before investigating persistent moderate-to-severe eosinophilia, as end-organ damage can be subclinical initially. 2

Document absolute eosinophil counts (not just percentages) and clearly define what constitutes "elevated" in your clinical context, as there is significant variability in defining "peripheral eosinophilia" with thresholds ranging from >350 to >800 eosinophils/mm³ across different studies. 3

Evaluate for concurrent atopic conditions (rhinitis, asthma, eczema) in all children with elevated eosinophils, as 50-80% will have multiple allergic manifestations. 3