Eosinophils - Kresser Institute Membership Site

Marker Name: Eosinophils

REFERENCE RANGES FOR EOSINOPHILS:

Laboratory reference range:
Relative 0–5%
Absolute 0.0–0.4 x10³/µL

Functional reference range:
Relative 0–3%
Absolute 0.0–0.4 x10³/µL

DESCRIPTION:

Eosinophils are one of the five major types of leukocytes (white blood cells), along with neutrophils, basophils, lymphocytes, and monocytes. Eosinophils are granulocytes, along with basophils and neutrophils.¹ Eosinophils are drawn to areas of inflammation through chemotaxis, at which point they activate and release substances contained within their granules. This degranulation adds substantially to the inflammatory response. These white blood cells secrete enzymes, growth factors, lipid mediators, and cytokines at sites of inflammation or infection, depending on the local milieu.² Eosinophils also release a number of reactive oxygen species and granule proteins that can destroy microbes.³ Unfortunately, these substances can also damage local tissues and cause excessive inflammation.^3,4

Development and maturation of eosinophils takes place within the bone marrow.² Upon maturation, eosinophils are released into the circulation; however, eosinophil numbers are relatively low in the vasculature. They are usually found in tissues surrounding the gut or occasionally in the lung.⁵ Eosinophils in the tissues can outnumber blood eosinophils by several hundred times.⁶ Eosinophils live for approximately eight to 18 hours within the circulation or between three to four days in tissues.⁷ At the end of their lifecycle, eosinophils undergo apoptosis. However, pro-inflammatory markers within tissues may delay programmed cell death and prolong the eosinophil’s lifespan.⁵

The absolute eosinophil count may be determined by multiplying the total WBC count by the percentage of eosinophils.² However, this approach can be problematic due to wide variations in absolute neutrophil counts among different ethnic groups.⁸ Moreover, eosinophil counts can vary within the same person at different times of the day or across different days.⁹ Importantly, eosinophil counts using peripheral blood may not correlate to tissue levels. While absolute eosinophil counts greater than 1,500 per microliter strongly suggest risk to organs and tissues, tissue damage may occur at lower blood eosinophil counts.¹⁰

An abnormally high eosinophil count in the blood is called eosinophilia. The causes of eosinophilia may be grouped into seven broad categories: infection, allergy, neoplasm, lung disorders, skin disorders, and miscellaneous conditions. Eosinophilia is most often associated with helminth parasite infections or infestations, though specific bacterial, fungal, and viral infections may also raise eosinophil counts in the blood.¹¹ Skin and lung disorders associated with eosinophilia are usually related to atopy or allergic hypersensitivity reactions. Hypersensitivity to virtually any prescription medication, nonprescription medication, dietary supplement, or herbal remedy can cause eosinophilia.¹² Very high eosinophil counts may denote a hypereosinophilic syndrome.¹³

Eosinopenia, or an abnormally low eosinophil count in the blood, is rather uncommon. It occurs most commonly in the context of an elevated neutrophil count during an acute infection.^14,15 Acute inflammation may also cause transient eosinopenia as eosinophils rapidly migrate from the blood to tissues.¹⁴ Corticosteroids, adrenergic drugs, and certain chemotherapeutics may decrease eosinophil counts. Erythropoietin deficiency, which is rare, may cause eosinopenia.^15,16

An eosinophil count is reported within the results of a complete blood count (CBC). In most cases, a standard CBC order includes an automated differential, which provides counts of the five main types of leukocytes, including eosinophils.¹⁷ A manual differential or peripheral blood smear may be ordered separately to quantify eosinophils along with other white blood cells. This test is performed manually by clinical staff.

PATHOLOGICAL/CONVENTIONAL RANGE INDICATIONS:

High in:^10,12,13

Infections
- Parasitic (most common)
- Bacterial
- Fungal
- Viral
Allergy and atopy
- Bronchial asthma
- Hay fever
- Urticaria
Drug hypersensitivity
Skin disorders
- Psoriasis
- Pemphigus
- Dermatitis herpetiformis
- Urticaria
- Angioedema
- Atopic dermatitis
Lung diseases
- Eosinophilic pneumonia
- Loeffler’s syndrome
- Churg–Strauss syndrome
- Tropical pulmonary eosinophilia
Hypereosinophilic syndrome
Systemic mastocytosis
Hypoadrenalism
Cholesterol embolization
Radiation exposure
Neoplastic
- Hodgkin lymphoma
- Chronic eosinophilic leukemia
- Lymphocytic leukemia
- Myelogenous leukemia
- Adenocarcinoma of various solid organs

Low in:^14-16

Acute infection (usually with concurrent neutrophilia)
Acute inflammation
Acute stress
Erythropoietin deficiency
Drugs
- Corticosteroids
- Adrenergic agents
- Chemotherapy

FUNCTIONAL RANGE INDICATIONS:

High in:

Same as conventional indications

Low in:

Same as conventional indications

References: