Absolute Eosinophil Count (AEC) Calculator
Absolute Eosinophil Count (AEC) Calculator
Turn a white cell count and an eosinophil percentage into the absolute eosinophil count, and read it against the thresholds that actually define eosinophilia and hypereosinophilia.
Absolute Eosinophil Count (AEC)
WBC × % eosinophilsWBC 9.8 ×10⁹/L, eosinophils 12%
Formula
- WBC
- white cell count, ×10⁹/L
- % eosinophils
- the eosinophil percentage from the differential
- 1.5 ×10⁹/L
- the consensus threshold for hypereosinophilia — an absolute count, never a percentage
- timing
- the count has a diurnal rhythm with a morning trough, and corticosteroids suppress it within hours, so when the sample was taken changes what it means
Worked example
WBC 9.8 ×10⁹/L, eosinophils 12%
9.8 × 12 ÷ 100 = 1.18 ×10⁹/L
12 per cent looks striking, but the absolute count is 1.18 — mild eosinophilia, below the 1.5 ×10⁹/L hypereosinophilia threshold
At this white cell count the percentage would have to reach about 15.3 per cent to cross 1.5 ×10⁹/L
Which is the point of the calculation: the threshold is written in absolute numbers, and the percentage cannot be read against it
Eosinophilia bands
| AEC (×10⁹/L) | Category | What follows |
|---|---|---|
| < 0.5 | Normal | No action from the count alone |
| 0.5 – 1.5 | Mild eosinophilia | Drug and travel history; atopy and helminths cover most of it |
| 1.5 – 5.0 | Hypereosinophilia, moderate | Confirm on a second sample ≥ 1 month later; search for end-organ damage |
| > 5.0 | Hypereosinophilia, severe | Urgent end-organ assessment including troponin and echocardiography; discuss with haematology |
What actually causes it
| Group | Examples | Note |
|---|---|---|
| Helminth infection | Strongyloides, hookworm, schistosomiasis, filariasis, toxocariasis | The commonest cause worldwide. Exclude strongyloidiasis before giving corticosteroids — they can precipitate fatal hyperinfection |
| Atopy | Asthma, atopic eczema, allergic rhinitis, allergic bronchopulmonary aspergillosis | The commonest cause in high-income settings, and rarely exceeds 1.5 ×10⁹/L on its own |
| Drugs | Antibiotics, allopurinol, anticonvulsants, NSAIDs, checkpoint inhibitors | DRESS is the reaction to recognise: rash, fever, eosinophilia and organ involvement |
| Immunological and vasculitic | Eosinophilic granulomatosis with polyangiitis, IgG4-related disease, adrenal insufficiency | EGPA in an asthmatic with new neuropathy or cardiac involvement |
| Neoplastic | Myeloid or lymphoid neoplasms with tyrosine kinase gene fusions, chronic eosinophilic leukaemia, lymphoma, solid tumours | Screen for PDGFRA, PDGFRB, FGFR1 and JAK2 rearrangements — imatinib-responsive disease is missed otherwise |
The threshold is an absolute number, and the timing of the sample changes it
The eosinophil percentage is not the measurement anyone means. A count of 12 per cent on a white cell count of 9.8 ×10⁹/L is an absolute eosinophil count of 1.18 ×10⁹/L, which is mild eosinophilia; the same 12 per cent on a white cell count of 20 would be 2.4 ×10⁹/L, which is hypereosinophilia and a different piece of work. Every threshold in this field is written in ×10⁹/L: below 0.5 is normal, 0.5 to 1.5 is mild eosinophilia, and 1.5 ×10⁹/L or above is hypereosinophilia, subdivided into moderate up to 5.0 and severe beyond it.
Worldwide the commonest cause is helminth infection, and in high-income settings it is atopy and drug reactions. That ordering makes the travel and residence history the first test rather than the last, and it makes one exclusion urgent: strongyloidiasis must be considered before corticosteroids are given, because immunosuppression can convert a chronic infection into fatal hyperinfection syndrome. Drug reactions deserve the same early attention, since the treatment is to stop the drug, and DRESS — rash, fever, eosinophilia and organ involvement — carries real mortality.
Two features of the sample itself change what the number means. Eosinophil counts follow a diurnal rhythm that runs inversely to cortisol, peaking at night and reaching their trough in the morning, which is when most outpatient blood is taken. And corticosteroids drop the count within hours, so a normal eosinophil count in someone already on steroids says almost nothing. Where the clinical picture suggests eosinophilia and the count is normal, the timing and the drug chart are worth checking before the result is accepted.
A count at or above 1.5 ×10⁹/L on two occasions at least a month apart, or tissue hypereosinophilia, defines hypereosinophilia; adding attributable end-organ damage defines hypereosinophilic syndrome. The organs to ask about are the heart, lungs, skin, nerves and gut, and the cardiac question is the pressing one, because eosinophilic myocarditis can be well advanced while the patient still feels well — a troponin and an echocardiogram are reasonable at any severe count. Alongside that, screening for PDGFRA, PDGFRB, FGFR1 and JAK2 rearrangements matters, because those neoplasms respond to tyrosine kinase inhibition and are otherwise missed.
Frequently asked questions
What absolute eosinophil count is abnormal?
Above 0.5 ×10⁹/L is eosinophilia. From 0.5 to 1.5 is mild; 1.5 ×10⁹/L or above is hypereosinophilia, moderate up to 5.0 and severe beyond it. The thresholds are absolute counts, so a percentage cannot be read against them.
What is the definition of hypereosinophilia?
A blood eosinophil count of 1.5 ×10⁹/L or above on two examinations at least one month apart, or marked tissue eosinophilia. Adding end-organ damage attributable to the eosinophils defines hypereosinophilic syndrome.
What causes a high eosinophil count?
Helminth infection is the commonest cause worldwide; atopy and drug reactions dominate in high-income settings. Beyond those, consider eosinophilic granulomatosis with polyangiitis, adrenal insufficiency, lymphoma and myeloid neoplasms with tyrosine kinase gene fusions.
Does a normal eosinophil count rule out eosinophilia?
Not if the patient is on corticosteroids, which suppress the count within hours, and not reliably from a single morning sample. Eosinophils follow a diurnal rhythm inverse to cortisol, peaking at night and troughing in the morning, when most blood is taken.
Why check for Strongyloides before giving steroids?
Because corticosteroids can convert a chronic, quiet strongyloidiasis into hyperinfection syndrome, which is frequently fatal. In anyone with eosinophilia and a history of residence or travel in an endemic area, serology should come before immunosuppression.
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References
- Valent P, Klion AD, Horny HP, et al. Contemporary consensus proposal on criteria and classification of eosinophilic disorders and related syndromes. J Allergy Clin Immunol. 2012;130(3):607–612.
- Klion AD. How I treat hypereosinophilic syndromes. Blood. 2015;126(9):1069–1077.