Evaluation of Hypereosinophilia

Initial Diagnostic Approach

The initial diagnostic approach for hypereosinophilia should include a detailed travel history, medication review, and calculation of absolute eosinophil count (AEC) from a complete blood count (CBC) with differential, as recommended by the American College of Physicians 1

Geographic exposure details should be documented, including timing relative to symptom onset, as eosinophilia typically appears 4-12 weeks post-exposure during tissue migration phases when stool studies may still be negative, according to the Centers for Disease Control and Prevention 1, 2
A medication timeline should be noted, including any recent additions within the past 3 months, as drug-induced eosinophilia is a common non-infectious cause, as reported by the Journal of Infection 3, 4, 5
Atopic history should be assessed, including asthma, eczema, and allergic rhinitis, which account for approximately 80% of eosinophilia cases in non-tropical populations, according to the American Academy of Allergy, Asthma, and Immunology 6, 2

Concentrated stool microscopy should be performed on three separate samples on different days, regardless of symptoms, as helminth infection causes 14-64% of eosinophilia in returning travelers, as recommended by the World Health Organization 3, 4, 1
Strongyloides serology is essential for all patients given the risk of fatal hyperinfection syndrome in immunocompromised hosts, even >50 years after exposure, according to the Infectious Diseases Society of America 3, 6
Schistosomiasis serology should be performed if freshwater exposure in endemic areas (particularly Africa) within the past 4-8 weeks, as recommended by the Centers for Disease Control and Prevention 1, 2

Hypereosinophilia (≥1.5 × 10⁹/L) is never explained by allergy alone and always requires comprehensive workup to exclude secondary causes, according to the American College of Physicians 6
Long-standing hypereosinophilia can cause significant end-organ damage affecting heart, lungs, CNS, and skin, as reported by the Journal of Infection 3, 4, 6

Eosinophilic myocarditis is the number one cause of morbidity and mortality in hypereosinophilic syndrome, presenting in 20% of cases, according to the American Heart Association 7
Cardiac evaluation is mandatory in hypereosinophilic syndrome given high mortality risk, as recommended by the American College of Cardiology 7

Universal screening for Strongyloides is essential given the risk of hyperinfection syndrome with mortality rates approaching 70% in immunocompromised patients, according to the Infectious Diseases Society of America 3, 6
Katayama syndrome should be suspected with freshwater exposure 4-8 weeks prior, fever, urticarial rash, and eosinophilia, as recommended by the Centers for Disease Control and Prevention 1

Refer to hematology if eosinophilia persists ≥1.5 × 10⁹/L for more than 3 months without identified cause after treatment or exclusion of infectious causes, as recommended by the American Society of Hematology 6