How Absolute Eosinophil Count is Obtained
The absolute eosinophil count (AEC) in pediatric patients is calculated by multiplying the percentage of eosinophils from the differential count by the total white blood cell count, yielding a result expressed as cells/μL or ×10⁹/L. 1
Calculation Method
The AEC is derived from routine complete blood count (CBC) with differential using the following formula: 1
- AEC (cells/μL) = Total WBC count × (% eosinophils ÷ 100)
For example, if a child has a WBC of 10,000 cells/μL and 5% eosinophils on differential, the AEC = 10,000 × 0.05 = 500 cells/μL 1
Technical Approaches
Two primary methods exist for obtaining eosinophil counts, both yielding comparable results: 2
- Automated differential count: Most commonly used in modern practice, performed as part of routine CBC with automated cell counters 1
- Manual hemacytometer count: Historically considered the gold standard but now rarely used; involves direct counting of eosinophils in a hemacytometer chamber 2
Studies demonstrate that calculated AEC from Wright-stained blood smears produces similar results to direct hemacytometer counts, validating the routine automated approach 2
Normal Reference Ranges in Pediatrics
In atopic children specifically, 20-100% may demonstrate elevated peripheral eosinophil counts, though elevations are typically modest (2-fold increase) 5
Critical Interpretation Points
Always report absolute counts, not just percentages, as the absolute number provides standardized, reproducible measurements that allow comparison across institutions and guide clinical decisions 3, 5
The percentage alone can be misleading—a child with leukopenia may have a normal percentage but low absolute count, while a child with leukocytosis may have an elevated percentage but normal absolute count 1
Common Pitfalls to Avoid
- Recent corticosteroid use: Can artificially lower eosinophil counts within 6 hours of administration, with 2- to 7-fold decreases observed 5, 4
- Timing of sample: Eosinophil counts demonstrate diurnal variation 1
- Concurrent infections or medications: Can suppress or elevate counts independent of allergic disease 1
Clinical Context for Pediatric Allergies
Peripheral blood AEC has significant limitations in pediatric allergy evaluation: 5
- Does not reliably correlate with tissue eosinophilia or disease activity
- Cannot distinguish between different allergic conditions (rhinitis, asthma, eczema all contribute to elevations)
- Thresholds for "elevated" vary widely across studies (>350 to >800 cells/μL)
Despite these limitations, AEC remains useful for monitoring treatment response—88% of pediatric patients with eosinophilic esophagitis show decreased blood eosinophil counts following corticosteroid treatment 5