Eosinophils
Eosinophils· also: Eosinophils, AEC
Clinical Overview
Eosinophils are white blood cells that primarily fight parasitic infections and modulate allergic responses. They are elevated in allergic conditions like asthma, atopic dermatitis, and hay fever, as well as in parasitic infections and some malignancies. The absolute eosinophil count (AEC) is more clinically useful than the percentage.
Why This Test Matters
Eosinophilia is a critical finding that narrows the differential to allergic, drug-related, parasitic, or malignant causes. Hypereosinophilic syndrome (AEC >1,500/µL persistently) can cause end-organ damage to the heart, lungs, skin, and nervous system. Tropical parasites (Ascaris, Strongyloides, Toxocara) should be excluded in any patient with unexplained eosinophilia and travel history.
Reference RangesWHO/IFCC standards
| Age Group | Reference Range | Unit | Notes |
|---|---|---|---|
| Adults (18–64) | 0.05 – 0.5 | ×10³/µL | — |
Also reported in: %.
What Causes Abnormal Results?
High Eosinophils Causes
- Allergic diseases: asthma, hay fever, atopic dermatitis, food allergy
- Parasitic infections: roundworm, hookworm, Strongyloides, Toxocara, Trichinella
- Drug hypersensitivity reactions
- Eosinophilic esophagitis or gastroenteritis
- Hypereosinophilic syndrome
- Churg-Strauss syndrome (eosinophilic granulomatosis with polyangiitis)
- Adrenal insufficiency (Addison's disease)
Low Eosinophils Causes
- Corticosteroid use (epinephrine and steroids redistribute eosinophils)
- Acute bacterial infections (eosinophils temporarily absent)
- Cushing's syndrome
Signs & Symptoms to Watch For
How to Prepare for This Test
No special preparation. Part of CBC differential. Avoid antihistamines before testing if allergy assessment is the reason for the test.
Factors That Can Affect Results
- Time of day (lowest in the morning, highest at night — circadian rhythm)
- Corticosteroids (significantly lower eosinophil count)
- Exercise (transient decrease)
Related Topics
Frequently Asked Questions
What parasite causes the highest eosinophil count?
Tissue-invasive parasites cause the highest eosinophilia, particularly Strongyloides stercoralis, Toxocara (visceral larva migrans), Trichinella spiralis, and filarial worms. Intestinal-only parasites like Giardia do not cause eosinophilia because they do not invade tissue. The degree of eosinophilia parallels the extent of tissue invasion.
Can high eosinophils damage the heart?
Yes. In hypereosinophilic syndrome with persistently elevated eosinophils, toxic granule proteins released from eosinophils can damage the myocardium, causing Löffler endocarditis — a serious and potentially fatal condition. Echocardiography is recommended when AEC is above 1,500/µL for more than 6 months.