What is Absolute Eosinophil Count (EOS Absolute)?
Absolute eosinophil count (AEC) is a calculated laboratory value representing the total number of eosinophils per microliter of blood, derived by multiplying the percentage of eosinophils by the total white blood cell count. 1
Definition and Calculation
- AEC is calculated as: (percentage of eosinophils) × (total WBC count) = absolute eosinophil count in cells/μL 1
- The term "absolute" distinguishes this from the percentage-based differential count, providing a standardized measurement that accounts for variations in total white blood cell counts 2
- Normal absolute eosinophil counts range from 50-500 cells/μL 2, 3
Clinical Thresholds and Interpretation
Blood Eosinophilia Classification
- Eosinophilia is defined as AEC >500 cells/μL 1
- Hypereosinophilia is defined as AEC ≥1,500 cells/μL 1, 4, 5, 6
- This threshold distinction is clinically important because hypereosinophilia rarely results from allergy alone and always warrants further workup 1
Tissue Eosinophilia (Esophageal Biopsies)
- For esophageal biopsies, absolute counts are expressed as eosinophils per 0.3 mm² (equivalent to one high-power field), with ≥15 eosinophils per 0.3 mm² being the diagnostic threshold for eosinophilic esophagitis 7, 2
- Peak (maximum) absolute counts from the most densely populated field are reported rather than average counts, as inflammation is often patchy and focal 7, 2
Why "Absolute" Matters Clinically
- Absolute counts provide standardized, reproducible measurements that allow comparison across institutions and studies 2
- Percentage-based eosinophil counts can be misleading when total WBC is abnormal—a patient with 5% eosinophils may have a normal AEC if leukopenic or elevated AEC if leukocytotic 1
- Specific absolute thresholds (e.g., 150 cells/μL, 300 cells/μL) guide treatment decisions for biologic therapies and inhaled corticosteroid use in conditions like COPD 2, 8
Reporting Standards
- Peripheral blood eosinophils should be reported as absolute counts in cells/μL or ×10⁹/L 2
- For esophageal biopsies, report the peak absolute eosinophil count per 0.3 mm² from the most densely populated area, along with other histologic features 7, 2
- Standardization to 0.3 mm² addresses historical variability in "high-power field" sizes across different microscopes 7, 2