Eosinophil Count: Why It’s Done and What It Means

Eosinophils are a type of white blood cell that play an important role in your body’s immune response to help fight off infection. Like other white blood cells, eosinophils are produced in the bone marrow and travel to different tissues throughout the body to protect against infection and disease.

In healthy individuals, eosinophils make up less than 5% of white blood cells circulating throughout the body. The body increases eosinophil production as an immune response to certain threats, such as allergies (e.g., food, environmental, medications); asthma; and parasitic, bacterial, and viral infections.

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. 

This article explains exactly what an eosinophil count is and what a high eosinophil count may mean. 

Gloved hand holding a blood draw tube with the label "eosinophils count (EC) test".

Md Ariful Islam / Getty Images

What Is an Eosinophil Count?

An eosinophil count (EOS blood test) is a blood test that measures the number of eosinophils in your body. Eosinophil levels can be measured through a routine complete blood count (CBC) test by multiplying the total white blood cell (WBC) count by the percentage of eosinophils.

Your eosinophil blood counts can vary at different times of day and on different days, but the variability in results is generally not a cause for concern, as this is normal. 

Why Would an EOS Blood Test Be Needed?

Your healthcare provider may order an EOS 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:

Procedure

The procedure for an eosinophil count is a straightforward lab blood test. A healthcare provider will draw from a vein, most typically from the inside of your elbow. The area where a needle will be inserted to draw blood is cleaned using an antiseptic to kill harmful bacteria. The healthcare provider will wrap an elastic band around your arm to help blood collect in the vein. 

Once the antiseptic has dried, the healthcare provider will insert a needle into your vein to collect the blood into a small glass tube (vial) attached to the needle. After the blood has been collected, the elastic band and needle will be removed from your arm. A cotton ball and bandaid will be placed on the area to stop bleeding. 

From there, your blood will be taken to a lab where it is placed on a microscope slide. A stain is added to the blood to ensure eosinophils are easily detected—they will appear as orange-red granules. A lab technician will count how many eosinophils are present per 100 cells and share the results with your doctor.

Is The Procedure Painful?

You may feel mild pain like a pinch or sting when the needle is inserted and withdrawn from your skin. You may also experience tenderness at the site for an hour or two after the blood is drawn. 

How to Prepare

There are no special steps (e.g., fasting) required to prepare for the EOS blood test. 

Tell your healthcare provider about any medications or over-the-counter supplements you are taking (e.g., vitamins, supplements, prescription medications) before your test. Certain medications can increase eosinophil counts, including:

  • Amphetamines, which are stimulant drugs such as Adderall (dextroamphetamine-amphetamine)
  • Antibiotics, which are medications that fight bacterial infections
  • Interferon, or signaling proteins your body naturally makes to fight viruses, which have been turned into drugs that are used for conditions such as melanoma skin cancer, hepatitis, and multiple sclerosis
  • Laxatives containing psyllium, a form of soluble fiber found in products like Metamucil, Fiberall, and Hydrocil
  • Tranquilizers, drugs used to reduce anxiety and tension, which include Valium (diazepam), Librium (chlordiazepoxide), and Xanax (alprazolam).

What Your Results Mean

The laboratory technician will send the results of your EOS test to your healthcare provider within a week. Your healthcare provider will review the results and share them with you. 

Normal Eosinophil Range

A normal absolute eosinophil count ranges from 0 to 500 cells per microliter (<0.5 x 109/L). This typically amounts to less than 5% of all white blood cells. Different laboratories may have different normal reference ranges. Your healthcare provider will explain your results and provide clarity if you have any questions. 

High Eosinophil Levels

An above-normal eosinophil count is known as eosinophilia. High eosinophil counts can range from mild to severe:

  • Mild: 500 to 1,500 eosinophil cells per microliter of blood
  • Moderate: 1,500 to 5,000 eosinophil cells per microliter of blood
  • Severe: 5,000 or more eosinophil cells per microliter of blood

Eosinophilia is associated with a variety of conditions and diseases. A high eosinophil count may be due to:

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

Low Eosinophil Levels

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.

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.

If you have low eosinophil counts with symptoms that may indicate an underlying health condition, your healthcare provider may order additional tests to provide an accurate diagnosis. 

Summary

Eosinophils are specialized white blood cells that help the body fight off infection. 

Eosinophil count tests are blood tests that can detect the number of eosinophils in the bloodstream. Your healthcare provider may order an EOS blood test if you're experiencing symptoms that indicate you may have elevated eosinophil levels. The blood test may also be used to help confirm a diagnosis if your healthcare provider suspects you have a certain condition or disease. 

High eosinophil counts—called eosinophilia—can be caused by a wide variety of conditions. Eosinophilia is most commonly associated with allergic disease, medication reactions, and parasitic infections. 

Treatment for the underlying cause of eosinophilia typically restores eosinophil levels within a normal range. 

A Word From Verywell 

It can be intimidating to learn that you have a high or low eosinophil count, especially when there are so many conditions that can contribute to it or come from it. Keep in mind that you're another step closer to diagnosis and finding the treatment that can help you feel better. Don't be afraid to ask questions; understanding your test results is an important part of being an informed patient.

Frequently Asked Questions

  • Can stress result in high eosinophils?

    High eosinophil counts are not associated with stress. In fact, stress may decrease eosinophil levels. High-stress situations cause the body to increase cortisol (stress hormone) production, which can cause a significant decrease in eosinophil counts.

  • Can certain foods increase eosinophil count?

    Allergic reactions to certain triggers—including foods—can increase eosinophil counts. If you eat a food you're allergic to, your body may produce more eosinophils in reaction to the allergen. Avoiding foods that trigger an allergic reaction can help you maintain normal levels of eosinophils in your body. 

  • Do you experience physical symptoms of high eosinophils?

    Mild eosinophilia (less than 1,500 eosinophil cells per microliter of blood) does not typically cause symptoms. Higher levels of eosinophils may cause asthma, diarrhea, itching, rash, and a runny nose. If high eosinophil levels are caused by an underlying health condition, you may have symptoms related to that disease.

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