What is the appropriate diagnostic and treatment approach for a patient with elevated eosinophils (high eosinophil count) on lab results?

Diagnostic and Management Approach for Elevated Eosinophils

For patients with elevated eosinophils, immediately assess for end-organ damage (cardiac, pulmonary, neurologic) and obtain a detailed travel history to exclude helminth infections, which account for 19-80% of cases in endemic-exposed patients, before proceeding with systematic evaluation based on eosinophil severity. 1

Immediate Red Flag Assessment

Any patient with eosinophilia presenting with the following requires urgent evaluation:

• Cardiac symptoms (chest pain, dyspnea, heart failure, arrhythmias) suggest eosinophilic myocarditis requiring immediate ECG, troponin, NT-proBNP, and echocardiography 2, 1
• Neurological deficits (altered mental status, focal weakness, peripheral neuropathy) demand immediate imaging and treatment 1
• Pulmonary involvement (persistent cough, wheezing, infiltrates on imaging) necessitates urgent pulmonary function tests and chest X-ray 1
• Absolute eosinophil count ≥5.0 × 10⁹/L at any time requires immediate evaluation regardless of duration 1

Severity-Based Diagnostic Algorithm

Mild Eosinophilia (0.5-1.5 × 10⁹/L)

Most commonly caused by allergic disorders or medications in non-endemic areas 1:

• Evaluate for asthma, allergic rhinitis, atopic dermatitis, or drug reactions 3
• In patients with travel history to endemic regions, helminth infections are the leading cause (19-80% of cases) 1
• Obtain three separate concentrated stool specimens for ova and parasites 1
• Send Strongyloides serology and culture immediately 1
• If fresh water exposure in Africa/tropical regions, add Schistosomiasis serology 1

Moderate to Severe Eosinophilia (≥1.5 × 10⁹/L)

This threshold defines hypereosinophilic syndrome and carries significant risk of end-organ damage 1, 4:

• Mandatory cardiac evaluation: ECG, cardiac troponin, NT-proBNP, and echocardiography to screen for myocardial injury 1
• If cardiac troponin elevated or clinical cardiac features present, obtain cardiac MRI 1
• Complete parasitic workup as above, even if asymptomatic 1
• If persisting >3 months after infectious causes excluded or treated, refer to hematology 1

Essential Travel and Exposure History

Obtain specific details about:

• Fresh water exposure in Africa or tropical regions (Schistosomiasis risk) 1
• Raw or undercooked meat consumption (helminth risk) 1
• Timing of travel relative to eosinophilia onset 1
• Geographic regions visited, particularly Strongyloides-endemic areas 1

Critical pitfall: Many helminth-infected patients do not have eosinophilia, so normal eosinophil counts do not exclude parasitic infection 1, 5

Organ Damage Assessment Protocol

For any patient with eosinophils ≥1.5 × 10⁹/L, systematically evaluate:

Cardiac

• ECG, troponin, NT-proBNP in all patients 1
• Echocardiography if troponin elevated or symptoms present 1
• Cardiac MRI when elevated troponin or clinical cardiac injury features 1

Pulmonary

• Pulmonary function tests if respiratory symptoms 1
• Chest X-ray to identify infiltrates 1
• Bronchoscopy with bronchoalveolar lavage if imaging suggests parenchymal disease 1

Neurologic

• Electromyography if sensory or motor deficits 1
• Nerve biopsy if EMG consistent with neuropathy 1

Gastrointestinal

• If dysphagia or food impaction: upper endoscopy with multiple biopsies (minimum 6: 2-3 proximal, 2-3 distal esophagus) to evaluate for eosinophilic esophagitis 1
• Peripheral eosinophilia occurs in only 10-50% of adults with eosinophilic esophagitis, so tissue diagnosis remains essential 1

Treatment Algorithm

For Helminth Infections (Endemic Exposure)

Empiric treatment when initial testing negative in returning travelers: Albendazole 400 mg single dose plus Ivermectin 200 μg/kg single dose 6

Confirmed Strongyloidiasis: Ivermectin 200 μg/kg daily for 2 days 1

Schistosomiasis: Praziquantel 40 mg/kg single dose, repeated at 6-8 weeks 1

Acute Katayama syndrome: Add prednisolone 20 mg daily for 5 days 1

CRITICAL WARNING for Loa loa: Do not use diethylcarbamazine if microfilariae seen on blood film—may cause fatal encephalopathy. Use corticosteroids with albendazole first to reduce microfilarial load to <1000/ml before definitive treatment 1

For Eosinophilic Esophagitis

First-line treatment: Topical swallowed corticosteroids (fluticasone or budesonide) decrease blood eosinophil counts in 88% of patients 1, 3

Maintenance therapy mandatory after achieving remission due to high relapse rates 1

Endoscopic dilation safe for fibrostenotic disease but must combine with anti-inflammatory therapy 1

For Hypereosinophilic Syndrome

After excluding secondary causes 4:

• Corticosteroids are first-line therapy for lymphocyte-variant hypereosinophilia and idiopathic HES 2, 4
• Imatinib for myeloid neoplasms with PDGFRA/PDGFRB rearrangements (exquisitely responsive) 4, 7
• Hydroxyurea or interferon-alfa for steroid-refractory cases 4

Hematology Referral Indications

Refer immediately if:

• Eosinophils ≥1.5 × 10⁹/L persisting >3 months after infectious causes excluded 1
• Any count >5.0 × 10⁹/L at any time 1
• Evidence of end-organ damage at any eosinophil level 1
• Suspected myeloid neoplasm (requires bone marrow biopsy, cytogenetics, molecular testing for PDGFRA/PDGFRB/FGFR1 rearrangements) 4, 7

Critical Pitfalls to Avoid

• Do not delay cardiac evaluation in moderate-to-severe eosinophilia—subclinical endomyocardial damage can occur 1, 7
• Do not assume eosinophilia alone screens for helminth infection—many infected patients have normal counts 1, 5
• Do not miss Strongyloides in immunocompromised patients—can cause fatal hyperinfection syndrome 1
• Do not rely solely on peripheral eosinophil counts for eosinophilic esophagitis—tissue biopsy is gold standard 1
• Do not wait for symptoms before investigating persistent moderate-to-severe eosinophilia—end-organ damage can be subclinical initially 1