Absolute Eosinophil Count

A high absolute eosinophil count (eosinophilia) usually signals allergic reactions, parasitic infections, certain medications, autoimmune diseases, or some cancers. It can cause symptoms like rashes, breathing problems, and gastrointestinal issues. Severe or persistent eosinophilia may damage organs (lungs, heart, nerves) and requires medical evaluation to identify the cause and start appropriate treatment to prevent complications.

Absolute eosinophil count (AEC) is calculated by multiplying the total white blood cell (WBC) count by the percentage of eosinophils from the differential, then dividing by 100. Units are cells per microliter (cells/µL). Example: WBC 6,000/µL with 3% eosinophils → AEC = 6,000 × 3 / 100 = 180 cells/µL.

Worry if your absolute eosinophil count (AEC) is persistently >500 cells/µL (0.5×10^9/L), and especially if it exceeds 1,500 cells/µL (1.5×10^9/L) or keeps rising. See a doctor sooner if you have symptoms—fever, weight loss, rashes, breathing or GI problems—or signs of organ involvement. Clinicians will repeat tests and investigate allergies, drugs, parasites, autoimmune disease or blood disorders.

High eosinophil counts (eosinophilia) may be asymptomatic or cause symptoms depending on the cause: skin rashes, itching, hives or eczema; nasal congestion and sinusitis; cough, wheeze or asthma flare-ups; gastrointestinal pain, nausea, diarrhea or weight loss; fever, fatigue and unexplained infections; and less commonly muscle weakness or nerve problems from organ involvement. Severity varies with the underlying condition.

Certain cancers can cause marked eosinophilia. Hematologic malignancies include Hodgkin lymphoma, T‑cell and other non‑Hodgkin lymphomas, chronic eosinophilic leukemia and other myeloproliferative neoplasms, and some acute leukemias. Paraneoplastic eosinophilia also occurs with solid tumors — notably lung, gastrointestinal, renal, ovarian and some head‑and‑neck cancers. Evaluation should assess both hematologic and solid‑tumor causes.

Treating high eosinophil counts focuses on finding and managing the underlying cause: treat parasitic infections with appropriate antiparasitics, stop or switch offending drugs, and control allergic inflammation with antihistamines, inhaled steroids or systemic corticosteroids for severe cases. For persistent or severe disease, refer to specialists—hematology/immunology—for further testing, immunosuppressants or targeted biologic therapies (e.g. anti‑IL‑5). Monitor counts and organ function.