What is the appropriate management for elevated eosinophil (white blood cell) counts?

Management of Elevated Eosinophil Count

Begin with a systematic evaluation based on the degree of eosinophilia and clinical presentation, prioritizing exclusion of parasitic infections in those with travel history, followed by assessment for allergic conditions, eosinophilic organ-specific disorders, and hematologic causes. 1

Initial Risk Stratification by Eosinophil Count

Mild eosinophilia (0.5-1.5 × 10⁹/L):

• Allergic disorders are the predominant cause, including asthma, allergic rhinitis, and atopic dermatitis 2
• Parasitic infections account for 19-80% of cases in patients with travel history to tropical regions 3
• A watch-and-wait approach with close follow-up is appropriate for asymptomatic patients without organ involvement 4, 5

Moderate to severe eosinophilia (≥1.5 × 10⁹/L):

• Requires urgent hematology referral if persisting >3 months after infectious causes are excluded 3
• Any count >5.0 × 10⁹/L requires immediate evaluation regardless of duration 3
• Cardiac evaluation is mandatory to detect endomyocardial involvement, which can be fatal 3, 6

Essential Diagnostic Workup

History and targeted evaluation:

• Obtain detailed travel history focusing on fresh water exposure in Africa, tropical regions endemic for Strongyloides stercoralis, and consumption of raw or undercooked meat 3
• Assess for gastrointestinal symptoms (dysphagia, food impaction) suggesting eosinophilic esophagitis 1
• Evaluate for allergic conditions including allergic rhinitis, atopic dermatitis, and asthma 1

Laboratory investigations:

• Stool microscopy for parasitic infections and serology for specific helminth infections (schistosomiasis, strongyloidiasis) based on travel history 1, 3
• Peripheral blood smear to assess eosinophil morphology and exclude myeloid neoplasms 3, 4
• Bone marrow evaluation with cytogenetics, FISH, and next-generation sequencing to detect PDGFRA, PDGFRB, FGFR1 rearrangements or PCM1-JAK2 fusion in persistent cases 4, 5

Cardiac assessment for eosinophilia ≥1.5 × 10⁹/L:

• ECG, echocardiogram, and troponin to detect endomyocardial involvement 3
• Delaying cardiac evaluation can lead to subclinical endomyocardial damage 3

Organ-specific evaluation:

• If gastrointestinal symptoms present, perform endoscopy with six biopsies from at least two different sites to evaluate for eosinophilic esophagitis (>15 eosinophils per 0.3 mm² diagnostic) 1
• Peripheral eosinophilia occurs in only 10-50% of adults with eosinophilic esophagitis, so normal blood counts don't exclude tissue disease 1, 2

Treatment Algorithm

For parasitic infections:

• Empiric treatment with albendazole 400 mg single dose plus ivermectin 200 μg/kg single dose for returning travelers with asymptomatic eosinophilia when initial testing is negative 1, 3
• For confirmed strongyloidiasis: ivermectin 200 μg/kg as a single dose 1
• For schistosomiasis: praziquantel 40 mg/kg single dose, repeated at 6-8 weeks, plus prednisone 20 mg daily for 5 days if Katayama syndrome present 3

For eosinophilic esophagitis:

• Topical steroids (fluticasone) decrease blood eosinophil counts in 88% of patients 1, 2
• Target histological remission defined as <15 eosinophils per 0.3 mm² 1
• Support from an experienced dietitian for two-food elimination diet for 8-12 weeks 1

For primary hematologic eosinophilia:

• Identification of PDGFRA or PDGFRB rearrangements is critical—these respond exquisitely to imatinib 4, 5
• Corticosteroids are first-line therapy for lymphocytic variant hypereosinophilia and idiopathic hypereosinophilic syndrome 4, 5
• Hydroxyurea and interferon-α for steroid-refractory cases 4, 5
• Mepolizumab (IL-5 antagonist) is FDA-approved for idiopathic hypereosinophilic syndrome 4

For allergic conditions:

• Optimize treatment for concomitant atopic disease 1
• Consider joint management by gastroenterologist and specialist allergy clinic for refractory cases with significant atopic disease 1

Critical Pitfalls to Avoid

• Missing Strongyloides in immunocompromised patients can lead to fatal hyperinfection syndrome 3
• Assuming normal peripheral eosinophil count excludes eosinophilic esophagitis—tissue biopsy remains the gold standard 1, 2
• Attributing all eosinophilia to allergies without excluding parasitic and hematologic causes results in delayed diagnosis 3
• Peripheral blood eosinophil counts may not correlate with tissue eosinophilia in organ-specific disorders 1, 2

Monitoring Response

• Obtain follow-up eosinophil counts after treatment to assess response 1
• If symptoms recur while on treatment, repeat endoscopy for assessment and obtain further histology 1
• Management strategies targeting eosinophil normalization reduce severe asthma exacerbations by up to 60% 2