Unit Converter
Eosinophils (EOS)
(Percentage of Total WBCs / Fraction / Proportion of 1.0)
Synonyms
- Eosinophils (%)
- EOS %
- Eosinophil proportion
- Eosinophil fraction
- Differential eosinophil count
- Relative eosinophil count
Units of Measurement
- % (percentage of total WBCs)
- Proportion of 1.0 (unitless fraction)
- Fraction (decimals, e.g., 0.03 = 3%)
Conversions
\text{EOS %} = \text{Fraction} \times 100 \text{Fraction} = \frac{\text{EOS %}}{100}
Description
Eosinophil percentage represents the relative proportion of eosinophils among total white blood cells (WBCs) in a complete blood count (CBC) with differential.
- Gives an overall picture of eosinophil proportion,
- But does NOT measure true eosinophil number (which is provided by Absolute Eosinophil Count – AEC).
Fractional eosinophil count is useful when analyzing:
- Allergic response patterns
- Type-2 inflammation
- Hematology trends
- Eosinophilia screening
Physiological Role
Eosinophils participate in:
- Allergic inflammation
- Parasitic defense
- Modulation of immune responses
- Chronic inflammatory conditions
- Asthma pathophysiology
Their percentage naturally varies through:
- Circadian rhythm
- Cortisol fluctuations
- Atopy/allergy exposure
Reference Intervals
(Tietz 8E + Hematology Standards + Mayo + ARUP)
Adults & Children (typical ranges)
- 1% – 5% of total WBCs
or - 0.01 – 0.05 as a fraction of 1.0
Interpretation
| EOS % | Fraction | Interpretation |
| <1% | <0.01 | Eosinopenia (often stress or steroids) |
| 1–5% | 0.01–0.05 | Normal range |
| >5% | >0.05 | Relative eosinophilia |
| >15% | >0.15 | Significant eosinophilia (check AEC) |
Important: Relative eosinophilia (%) can occur even when the absolute eosinophil count is normal, especially if total WBC is low.
Clinical Significance
Low Eosinophil % (Relative Eosinopenia)
Common and usually benign.
Causes:
- Acute stress response
- Sepsis or severe infection
- Cushing's syndrome / corticosteroids
- Adrenal hyperfunction
- Hypercortisolism
High Eosinophil % (Relative Eosinophilia)
May indicate increased eosinophil activity or decreased total WBC.
Common Causes
1. Allergic Diseases
- Asthma
- Allergic rhinitis
- Atopic dermatitis
- Food/drug allergy
2. Parasitic Infections
- Strongyloides
- Hookworm
- Schistosoma
- Filariasis
3. Skin Diseases
- Eczema
- Pemphigoid
- Drug rashes
4. Autoimmune / Vasculitic Conditions
- EGPA (Churg–Strauss)
- Eosinophilic pneumonia
- Eosinophilic fasciitis
5. Hematologic Conditions
- Hypereosinophilic syndrome (HES)
- Myeloid neoplasms
6. Endocrine Causes
- Adrenal insufficiency
Units Description
% (Percentage)
- EOS% = (Eosinophils ÷ Total WBCs) × 100
Fraction (Proportion of 1.0)
- Decimal form of eosinophil percentage
e.g., 0.04 = 4%
Relation to Absolute Count (AEC)
AEC=EOS%×WBC (cells/µL)100AEC = EOS\% \times \frac{WBC\ (\text{cells/µL})}{100}AEC=EOS%×100WBC (cells/µL)
Example:
WBC 8000/µL, EOS 6%
→ AEC = 0.06 × 8000 = 480 cells/µL (normal)
Diagnostic Uses
1. Screening for Atopy & Allergic Diseases
EOS % supports diagnosis but AEC and ECP are more specific.
2. Parasite Screening
Elevated EOS% + travel history → evaluate for helminths.
3. Asthma Endotyping
Relative eosinophilia suggests type-2 (eosinophilic) asthma.
4. Inflammatory Disorders
Used to track eosinophilic disorders and therapeutic response.
5. CBC Trends
Eosinophil percentage helps interpret:
- Diurnal variation
- Steroid effects
- Bone marrow response
Analytical Notes
- Automated hematology analyzers report % and absolute counts
- Manual microscopy may be needed if flags present
- Cortisol levels influence eosinophil percentages
- EOS % should always be interpreted with AEC
Clinical Pearls
- Percentage alone can be misleading; always check absolute eosinophil count.
- A high EOS % in the presence of low WBC may give false impression of eosinophilia.
- EOS % rises during night-time and early morning (inverse of cortisol).
- Corticosteroids drop EOS % rapidly - useful for monitoring steroid response.
- EOS % is helpful in asthma control assessment along with FeNO and IgE.
Interesting Fact
Eosinophils were first identified by Paul Ehrlich in 1879 due to their bright pink staining with eosin dye, giving rise to the name “eosin-ophils.”
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Hematology & Immunology.
- AAAAI/WAO Allergy and Asthma Guidelines.
- Mayo Clinic Laboratories - CBC Interpretation.
- ARUP Consult - Eosinophilia.
- Hematology Texts - Differential Leukocyte Analysis.