What is EOS Absolute in a Blood Test?
EOS Absolute (Absolute Eosinophil Count or AEC) is a calculated value that represents the actual number of eosinophils—a type of white blood cell—circulating in your blood, expressed as cells per microliter (cells/μL) or ×10⁹/L. 1
How It Is Calculated
- The absolute eosinophil count is calculated by multiplying the percentage of eosinophils (from the differential count) by the total white blood cell count 1
- For example: If your total WBC is 10,000 cells/μL and eosinophils are 5% of the differential, your AEC = 10,000 × 0.05 = 500 cells/μL 1
Normal Range and Clinical Thresholds
- Normal absolute eosinophil counts range from 50-500 cells/μL 2
- Eosinophilia is defined as an AEC >500 cells/μL (some references use >350-800 cells/μL depending on the laboratory) 1, 2
- Hypereosinophilia is defined as an AEC ≥1,500 cells/μL, which always warrants further investigation 1, 3
Why Absolute Count Matters More Than Percentage
- Absolute counts provide standardized, reproducible measurements that allow comparison across institutions and are used to monitor treatment response 2
- A percentage alone can be misleading—you could have a high percentage but low total WBC, resulting in a normal absolute count, or vice versa 1
- Specific absolute thresholds (e.g., 150 cells/μL, 300 cells/μL) guide clinical decisions, particularly for biologic therapy in conditions like asthma 2
Common Clinical Significance
- Mild eosinophilia (500-1,500 cells/μL) is most commonly caused by allergic disorders or medications in non-endemic areas 4
- In returning travelers or migrants, helminth (parasitic worm) infections account for 19-80% of eosinophilia cases 4
- Hypereosinophilia (≥1,500 cells/μL) is rarely explained by allergy alone and should always prompt further workup 1
- The vast majority of eosinophilias detected in ambulatory outpatients are associated with allergic processes 5
Important Caveats About Interpretation
- Peripheral blood eosinophilia occurs in only 10-50% of adults with eosinophilic esophagitis, so normal blood counts do not exclude tissue eosinophilia 4, 2
- Several factors influence eosinophil counts: nasal polyps increase levels by 38%, current smoking decreases levels by 23%, and substantial seasonal variation exists (∼20% difference between July and January) 6
- A single measurement may not be sufficient for diagnosis or management, particularly when counts fall in the 150-299 cells/μL range, which shows the least stability over time 6
- Eosinophil counts can be reduced with longer time from blood collection to laboratory analysis 6
When to Be Concerned
- Any AEC ≥1,500 cells/μL persisting for more than 3 months, or exceeding 5,000 cells/μL at any time, carries significant risk of end-organ damage 4
- Symptoms suggesting end-organ involvement (chest pain, dyspnea, persistent cough, neurological deficits, or gastrointestinal symptoms like dysphagia) with any degree of eosinophilia require urgent evaluation 4
- Moderate to severe eosinophilia (≥1,500 cells/μL) requires referral to hematology if it persists for more than 3 months after infectious causes have been excluded or treated 4