Synopsis
Interpret persistent eosinophilia and basophilia by absolute count, tempo and organ involvement, distinguish reactive from clonal disease and escalate eosinophilic organ injury or a myeloid-neoplasm phenotype promptly.
- Use absolute eosinophil and basophil counts, not percentages, and confirm persistence and trajectory. A high percentage during neutropenia may represent a normal absolute population.
- Eosinophilia is most often reactive to allergy, asthma, medicines or infection, but severity, duration, constitutional symptoms, splenomegaly and organ injury determine the need for clonal testing.
- Take a precise medicine timeline including antibiotics, anticonvulsants, allopurinol, supplements and recent stopped drugs; systemic drug hypersensitivity can continue after the culprit is withdrawn.
- Travel and residence history should identify helminth risk, freshwater, soil, raw food and animal exposure. Send species-directed tests with infectious-disease or microbiology advice rather than an indiscriminate parasite panel.
- Eosinophil count does not measure organ damage. Ask about chest pain, dyspnoea, neuropathy, rash, abdominal symptoms, fever, thrombosis and weight loss and examine heart, lungs, skin, nerves, nodes and spleen.
- Persistent basophilia is uncommon in ordinary allergy and is a strong clue to myeloid disease when accompanied by neutrophilia, left shift, thrombocytosis, splenomegaly or constitutional symptoms.
- The first clonal branch uses film, BCR::ABL1 and phenotype-directed molecular testing, followed by marrow morphology and genetics when a myeloid neoplasm remains plausible.
- In organ-threatening eosinophilic disease, take blood, molecular, infection and tissue samples promptly, then use specialist-directed corticosteroid or targeted treatment without waiting for every slow result.
Key red flags
Fever, widespread rash, facial oedema, lymphadenopathy, liver or kidney injury after a medicine suggests DRESS or another systemic hypersensitivity syndrome.
Chest pain, heart failure, neuropathy, pulmonary infiltrates, thrombosis or progressive organ dysfunction with eosinophilia indicates a time-critical eosinophilic syndrome.
Adult asthma, sinus disease, pulmonary infiltrates, neuropathy, purpura or renal and cardiac involvement raises eosinophilic granulomatosis with polyangiitis.
Investigation priorities
Confirm persistence, verify basophils and identify reactive or clonal accompanying changes.
Management branches
Eosinophilia accompanies cardiac, respiratory, neurological, thrombotic or rapidly progressive systemic disease.
- Use ABCDE and obtain urgent FBC, film, renal, liver, coagulation, troponin, ECG and phenotype-led imaging, involving haematology plus the threatened-organ specialty immediately.
- Take parasite, molecular, flow and tissue samples before treatment where feasible; preferred initial anti-inflammatory treatment is specialist-directed systemic corticosteroid when eosinophilic organ injury is strongly supported.
- If Strongyloides exposure is credible, arrange urgent infectious-disease assessment and treatment alongside immunosuppression decisions; escalate shock, myocarditis, hypoxaemia or neurological deficit to critical care.