Should You Order a CT Scan for an Asymptomatic Patient with Eosinophilia?
No, CT scanning is not recommended for asymptomatic patients with eosinophilia; instead, obtain three separate concentrated stool specimens for ova and parasites, Strongyloides serology, and schistosomiasis serology if there is any history of freshwater exposure in Africa, as these investigations identify the most common and treatable causes of eosinophilia without radiation exposure. 1, 2
Initial Diagnostic Approach for Asymptomatic Eosinophilia
The cornerstone of evaluation is identifying the underlying cause through targeted laboratory testing rather than imaging:
Obtain three separate concentrated stool specimens collected on consecutive days for ova and parasite examination, as helminth infections account for 19-80% of eosinophilia in returning travelers and migrants, and a single negative stool test has only 50% sensitivity 1, 2, 3
Order Strongyloides serology immediately in all patients with any travel history to tropical/subtropical regions, as this parasite can persist lifelong asymptomatically and cause fatal hyperinfection syndrome if immunosuppression is later required 1, 2, 3
Obtain schistosomiasis serology when there is any history of freshwater swimming in African lakes or rivers, even if asymptomatic, as chronic infection can lead to hepatosplenic disease 1, 2, 4
Risk Stratification by Eosinophil Count
The absolute eosinophil count (AEC) determines urgency and specialist referral needs:
Mild eosinophilia (0.5-1.5 × 10⁹/L) can be managed in primary care after appropriate workup if the patient remains asymptomatic and has no end-organ damage 3
Hypereosinophilia (≥1.5 × 10⁹/L) requires hematology referral if it persists for more than 3 months after excluding and treating infectious causes, regardless of symptoms 3, 5, 6
Hypereosinophilia is never explained by allergy alone and always requires investigation to exclude secondary causes (parasites, drugs, malignancy) and primary causes (myeloproliferative disorders) 4, 5
When CT Imaging IS Indicated
CT scanning becomes appropriate only when specific clinical scenarios develop:
Acute schistosomiasis (Katayama syndrome) with fever, urticaria, hepatosplenomegaly, and marked eosinophilia 4-8 weeks after freshwater exposure in Africa may show hepatic lesions characteristic of fluke migration through the liver 1
Abdominal ultrasound (not CT) is the preferred initial imaging for suspected hepatosplenic schistosomiasis in migrants with chronic infection 1, 2
Chest radiograph (not CT) is indicated if respiratory symptoms develop to identify migratory pulmonary infiltrates from larval migration (Loeffler's syndrome) 1, 2, 7, 8
CT chest may be considered if chest radiograph is negative or equivocal but clinical suspicion for eosinophilic lung disease remains high with respiratory symptoms 1, 7, 8
Essential History Elements to Guide Testing
Document specific exposures that determine which serologic tests to order:
Exact timing and location of freshwater swimming in Africa (schistosomiasis risk with 2-9 week incubation for acute disease) 1, 2, 4
Walking barefoot on soil or sand in tropical/subtropical regions (hookworm and Strongyloides with weeks-to-months incubation) 1, 2
Consumption of raw or undercooked meat (beef tapeworm, pork tapeworm/cysticercosis, fish flukes) 1, 2
All medications started within the past 3 months, particularly NSAIDs, beta-lactam antibiotics, and nitrofurantoin, as drug reactions are common causes 4
Additional Laboratory Workup
Beyond stool and serology, obtain:
Complete blood count with differential to calculate absolute eosinophil count and review peripheral smear for dysplasia, monocytosis, or circulating blasts suggesting myeloproliferative disease 4, 9, 5
Serum tryptase and vitamin B12 levels if hypereosinophilia (≥1.5 × 10⁹/L) is present, as elevated levels are characteristic of PDGFRA/PDGFRB rearrangements that respond to imatinib 4, 5, 6
Comprehensive metabolic panel with liver function tests to assess for organ damage even in asymptomatic patients 4
Critical Pitfalls to Avoid
Never assume a single negative stool test excludes helminth infection—three consecutive specimens are required for adequate sensitivity 1, 2, 3
Never initiate immunosuppressive therapy (including corticosteroids) without first screening for Strongyloides in patients from endemic areas, as this can precipitate fatal hyperinfection syndrome 1, 2, 3
Recognize that eosinophilia may be transient during tissue migration phases and can resolve when parasites reach the intestinal lumen, creating false reassurance despite active infection 1, 2
Serology becomes positive 4-12 weeks after infection—early testing may yield false-negative results, so timing matters 2, 4
Follow-Up Strategy for Asymptomatic Patients
Recheck absolute eosinophil count in 3 months if initial workup is negative and eosinophilia is mild 3
Instruct patients to return immediately if any symptoms develop: dysphagia, abdominal pain, rash, neurologic symptoms, cardiac symptoms, or respiratory symptoms 3
Refer to hematology if eosinophilia ≥1.5 × 10⁹/L persists beyond 3 months after excluding/treating infectious causes 3, 5