Eosinophil count optimal range and reference range
Compiled by Alina Radu, founder of Sera, from the published sources below · Last reviewed November 9, 2026
Sera's bands for Eosinophil count:
- Optimal 0.05 – 0.3 ×10⁹/L (0.05 – 0.3 ×10³/μL); sufficient 0.02 – 0.5 ×10⁹/L (0.02 – 0.5 ×10³/μL); out of range above 0.5 ×10⁹/L.
Evidence grade: Established clinical threshold. A band edge that corresponds to a recognised diagnostic, risk or treatment threshold from a major clinical guideline or public-health body.
All units
| Unit | Optimal | Sufficient | Out of range |
|---|---|---|---|
| ×10⁹/L | 0.05 – 0.3 | 0.02 – 0.5 | above 0.5 |
| ×10³/μL | 0.05 – 0.3 | 0.02 – 0.5 | above 0.5 |
| K/μL | 0.05 – 0.3 | 0.02 – 0.5 | above 0.5 |
| /mm³ | 50 – 300 | 20 – 500 | above 500 |
| x E9/L | 0.05 – 0.3 | 0.02 – 0.5 | above 0.5 |
Bounded on the high side only — a low result is not treated as out of range. Most laboratories and medlineplus start the normal interval at zero and no source defines a low eosinophil threshold.
What the evidence says
The acceptable band ends at 0.5, the level above which a count is conventionally called eosinophilia (500 cells per microlitre). A low eosinophil count has no accepted threshold: most laboratories start the normal interval at zero. The optimal ceiling of 0.3 is a functional target with no outcome evidence found. Eosinophils rise with allergies, asthma and parasitic infections and vary with allergic activity, so the count is read alongside the total white cell count, and a trend matters more than a single value.
Sources
- Eosinophil count - absolute — MedlinePlus Medical Encyclopedia, US National Library of Medicine, 2025 · Government / public-health guidanceA normal eosinophil count is less than 500 cells per microlitre, with no lower limit. Matches Sera's sufficient upper edge of 0.5 ×10⁹/L.
- Eosinophilia — NHS Dumfries and Galloway, DGRefHelp (Right Decisions, NHS Scotland), 2024 · Clinical guidelineThe normal range for eosinophils is 0.0 to 0.5 ×10⁹/L and eosinophilia is a count above 0.5; persistent counts of 1.5 or more are referred. Matches Sera's sufficient upper edge and gives no lower limit.
- White Blood Count — North Bristol NHS Trust, Severn Pathology, 2026 · Laboratory / reference-interval sourceAdult eosinophils 0.0 to 0.5 ×10⁹/L. Matches Sera's sufficient upper edge; the lower limit is zero. The page shows no review date; 2026 is the footer year.
- FBC — University Hospitals Sussex NHS Foundation Trust, Pathology, 2022 · Laboratory / reference-interval sourceAdult eosinophils 0 to 0.5 ×10⁹/L. Matches Sera's sufficient upper edge; the lower limit is zero.
- AUTO DIFF (test catalog entry) — MHCC Laboratory, test catalog powered by Mayo Clinic Laboratories, 2026 · Laboratory / reference-interval sourceAdult absolute eosinophils 0.05 to 0.5 ×10³/μL. The upper limit matches Sera's sufficient edge; its lower limit of 0.05 equals Sera's optimal lower edge, as one laboratory's reference limit. The page shows no review date; 2026 is the copyright year.
What Eosinophils # measures
The number of eosinophils, white blood cells that fight parasites and drive allergic reactions.
High eosinophils are linked to allergies, parasite infections, and autoimmune conditions. Worth noting alongside other inflammation markers.
Related blood cell health markers
- RBC # (Red Blood Cell Count)
- Hemoglobin (HGB)
- Hematocrit (HCT)
- Mean Corpuscular Volume (MCV)
- Mean Corpuscular Hemoglobin (MCH)
- Mean Corpuscular Hemoglobin Concentration (MCHC)
- RDW (Red Cell Distribution Width)
- WBC # (White Blood Cell Count)
- Neutrophils #
- Lymphocytes #
- Monocytes #
- Basophils #
- Neutrophils %
- Lymphocytes %
- Monocytes %
- Eosinophils %
- Basophils %
- Immature Granulocytes %
- Platelets (Thrombocytes)
- PCT (Plateletcrit)
- Reticulocytes (Absolute)
- Reticulocytes (%)
- Ferritin
- Iron (Serum)
- Transferrin
- TIBC (Total Iron Binding Capacity)
- Transferrin Saturation
- UIBC (Unsaturated Iron Binding Capacity)