Eosinophils "Eos" (Percent)

Optimal Result: 0 - 6 %.

What are Eosinophils?

Eosinophils are a type of white blood cell (leukocytes) that protect your body from parasites, allergens, foreign bacteria and outside organisms. Eosinophils are larger than most cells and make up less than 5% of all white blood cells in your body. An increased number of eosinophils may mean your body is fighting an infection or allergic reaction. Very high numbers may indicate a serious health condition.

Eosinophils have a role in defending your body from:

- fungal infections

- bacterial infections

- viral infections

- parasites, such as worms

In the immune system, eosinophils destroy invading germs like viruses, bacteria, or parasites, such as hookworms. They also have a role in the inflammatory response, especially if an allergy is involved. Eosinophils significantly contribute to inflammation related to allergies, eczema, and asthma. Inflammation helps isolate and control the immune response at an infection site but causes a side effect of tissue damage around it. Allergies are immune responses that often involve chronic inflammation.

What are white blood cells?

There are three types of white blood cells, all with various functions to help your immune system, including granulocytes, lymphocytes and monocytes. Eosinophils are one of three types of granulocytes, along with neutrophils and basophils. Eosinophils prevent foreign organisms from growing inside of host cells (parasites).

White blood cells are an important part of your immune system. They help protect you from bacteria, viruses, and parasites.

Your bone marrow produces all five kinds of white blood cells. It continually replenishes the white blood cell supply. Each white blood cell lives in the bloodstream for several hours to days.

The number and type of each white blood cell in your body can give doctors a better understanding of your health. Elevated levels often mean your body is sending more white blood cells to fight off infections.

What is an Eos Count (Absolute)?

An Eosinophil count (the absolute number) is a blood test typically ordered as part of a white blood cell count (WBC) with a differential. This test shows how many of each type of blood cell are circulating in your bloodstream. A doctor may order a WBC and a complete blood count (CBC) to get a good picture of your overall health.

Knowing your eosinophil count can help doctors determine how many eosinophils, a type of white blood cell, are in your bloodstream. A high number may mean that your immune system is fighting some kind of infection from a virus, bacteria, or fungus or experiencing an allergic reaction. It may also be a sign of another health condition, such as an autoimmune disease.

Why do I need an Eosinophil count?

A doctor may discover atypical eosinophil levels through a WBC with differential. A WBC differential test is often done alongside a CBC and determines the percentage of each type of white blood cell in your blood. This test will show if you have a high or low count of white blood cells. White blood cell counts can vary if you have certain diseases or health conditions. Your healthcare provider may order an Eosinophil blood test if you're experiencing symptoms that indicate you may have elevated eosinophil levels, such as:

- Diarrhea

- Itching

- Fever

- Rash

- Runny nose (particularly if allergy-related) 

- Weight loss

If your healthcare provider suspects you have a certain condition or disease, they may order the Eos blood test to check eosinophil levels. 

Conditions that can cause elevated eosinophils include:

- Asthma

- Allergies

- Certain cancers (e.g., Hodgkin's lymphoma, leukemia) 

- Drug sensitivities

- Eczema

- Parasitic infection

What are the functions of Eosinophils?

Eosinophil cells contain small sand-like granules that release a toxic protein to destroy and consume invading organisms. Eosinophils help your body defend itself from:

- Infections by parasites (strongyloidiasis, pinworms).

- Organisms that grow on other cells (intracellular bacteria).

- Exposure to allergens (immediate hypersensitivity reactions).

Eosinophils increase inflammation to help the body fight off infection and disease. But having too many eosinophils for a long period of time can cause chronic inflammation, which may lead to tissue damage and/or chronic health conditions. 

Where are Eosinophils located?

Eosinophils are a type of white blood cell that lives in your body’s tissues. 

The most common place to find eosinophils include:

- Blood

- Bone marrow

- Fat (adipose tissue).

- Lungs

- Skin

- Stomach

What do Eosinophils look like?

- Eosinophils are microscopic cells that are spherical. The cells are clear in your body but under a microscope, an acidic dye changes the cell’s color to be examined. The dye changes the cell to a purple or pink color.

- Eosinophils are larger than other cells and stand out because of their two-lobed nucleus, which looks like two separate raindrops connected by a thread. The nucleus contains the cell’s DNA and floats in a protein that appears sandy in texture (granules).

How many eosinophils are in your body?

Eosinophils are a type of white blood cell. White blood cells make up 1% of the cells in your body. There are less than 5% of eosinophils circulating among white blood cells in healthy adults.

What is the normal reference range of Eosinophils:

A normal absolute eosinophil count ranges from 0 to 400 cells per microliter (<0.4 x 109/L). 

An additional note on reference ranges:

The percentage (%) reference ranges for Eosinophils has not been officially established by most laboratories. If ranges have not been established by your laboratory, please refer to your Eosinophils absolute count.


Eosinophilia. Merck Manual Professional Version. https://www.merckmanuals.com/professional/hematology-and-oncology/eosinophilic-disorders/eosinophilia. Accessed Aug. 15, 2019.

Weller PF, et al. Eosinophil biology and causes of eosinophilia. https://www.uptodate.com/contents/search. Accessed Aug. 15, 2019.

Jameson JL, et al., eds. Disorders of granulocytes and monocytes. In: Harrison's Principles of Internal Medicine. 20th ed. The McGraw-Hill Companies; 2018. https://accessmedicine.mhmedical.com. Accessed Aug. 15, 2019.

McPherson RA, et al., eds. Leukocytic disorders. In: Henry's Clinical Diagnosis and Management by Laboratory Methods. 23rd ed. Elsevier; 2017. https://www.clinicalkey.com. Accessed Aug. 15, 2019.

Taylor MR, Keane CT, O'Connor P, Mulvihill E, Holland C. The expanded spectrum of toxocaral disease. Lancet. 1988 Mar 26; 1(8587):692-695. PubMed 2895221

Limaye AP, Abrams JS, Silver JE, Ottesen EA, Nutman TB. Regulation of parasite-induced eosinophilia: selectively increased interleukin 5 production in helminth-infected patients. J Exp Med. 1990 Jul 1; 172(1):399-402. PubMed 2193099

Colby TV, Carrington CB. Infiltrative lung disease. In Thurlbeck WM, ed. Pathology of the Lung. New York, NY: Thieme Medical Publishers Inc;1988:425-517.

Pavli P, Doe WF. The alimentary tract in disorders of the immune system. In Whitehead R, ed. Gastrointestinal and Oesophageal Pathology. Edinburgh, Scotland: Churchill Livingstone; 1989:187.

Centers for Disease Control and Prevention. Eosinophilia-myalgia syndrome−New Mexico. MMWR. 1989 Nov 17; 38(45):765-767. PubMed 2509886

Centers for Disease Control and Prevention. Eosinophilia-myalgia syndrome and L-tryptophan-containing products−New Mexico, Minnesota, Oregon and New York. MMWR. 1989 Nov 24; 38(46):785-788. PubMed 2509891

Kilbourne EM, Rigau-Perez JG, Heath CW Jr, Zack MM, Falk H, Martin-Marcos M, de Carlos A. Clinical epidemiology of toxic-oil syndrome: Manifestations of a new illness. N Engl J Med. 1983 Dec 8; 309(23):1408-1414. PubMed 6633617

What does it mean if your Eosinophils "Eos" (Percent) result is too low?

An abnormally low eosinophil count can be the result of:

- Intoxication from alcohol

- Excessive production of cortisol, like in Cushing’s disease. Cortisol is a hormone naturally produced by the body. Cushing's syndrome occurs when the body has too much cortisol (stress hormone) over a long period of time. High levels of cortisol suppress the immune system and may reduce eosinophil counts.

- Low eosinophil counts may also be due to the time of day. Under normal conditions, eosinophil counts are lowest in the morning and highest in the evening.

Unless alcohol abuse or Cushing’s disease is suspected, low levels of eosinophils are not usually of concern unless other white cell counts are also abnormally low. If all white cell counts are low, this can signal a problem with the bone marrow.

Long-term treatment for an underlying health condition may be necessary if your low eosinophil count does not return to normal on its own. Your body will often detect a low number of eosinophils on its own and other members of your immune system will step up to compensate for the lack of eosinophil cells. 

Eosinophils are normally low in healthy adults. However, certain health conditions and medications may suppress eosinophil levels. Corticosteroids and other immune system suppressant medications can reduce the production and function of eosinophils.

What does it mean if your Eosinophils "Eos" (Percent) result is too high?

What is a high eosinophil count?

A high eosinophil count is called eosinophilia and is classified by severity into three categories:

Mild: 500–1,500 eosinophil cells per mL

Moderate: 1,500–5,000 eosinophil cells per mL

Severe: greater than 5,000 eosinophil cells per mL

Eosinophilia can occur due to any of the following:

- Infection by parasitic worms

- Autoimmune disease

- Severe allergic reactions

- Eczema

- Asthma

- Seasonal allergies

- Leukemia and certain other cancers

- Hodgkin’s lymphoma, also known as Hodgkin’s disease

- Ulcerative colitis

- Scarlet fever

- Lupus

- Crohn’s disease

- Significant drug reaction

- Organ transplant rejection

- Adrenal gland deficiency 

- Hypereosinophilic syndromes (group of disorders characterized by high eosinophil counts and organ damage from eosinophilia)

- Parasitic infection

- Vasculitis

Having a very high number of eosinophils can be an emergency. Untreated, it may cause damage to multiple organs.

Does a high eosinophil count indicate cancer?

Although rare, having a consistently high eosinophil count can be an indication of cancer in your body. A high eosinophil count could relate to several cancers including:

- Breast

- Colorectal

- Cervical

- Hodgkin lymphoma

- Ovarian

- Prostate

If your healthcare provider suspects cancer, they will perform further tests to diagnose and treat the condition, like a biopsy, additional blood tests or imaging tests.

What are common treatments for a high eosinophil count?

- Treatment for eosinophilia depends on the cause. Your healthcare provider may order additional tests to provide an accurate diagnosis and treatment.

- Treatment for conditions with a high eosinophil count varies depending on the location and severity of the diagnosis. 

- Treatment to reduce a high eosinophil count can additionally include:

Avoiding certain types of foods for esophagitis including fatty, spicy and acidic foods.

Stopping or changing the dose of a medication if you had a drug reaction.

Taking anti-inflammatory medications.

Most high eosinophil count conditions are chronic and require long-term treatment and management.

How can I keep my eosinophils healthy?

Take steps to keep your eosinophil cells healthy by:

- Avoiding allergens.

- Eating a well-balanced diet

- Limiting alcohol intake.

- Practicing proper hygiene like washing your hands regularly.

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