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.
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:
DiarrheaItchingFeverRashRunny 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
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.
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 bloodModerate: 1,500 to 5,000 eosinophil cells per microliter of bloodSevere: 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:
Adrenal gland deficiency Allergies Asthma Autoimmune diseases Eczema Hodgkin’s lymphoma, also known as Hodgkin’s disease Hypereosinophilic syndromes (group of disorders characterized by high eosinophil counts and organ damage from eosinophilia) Leukemia Parasitic infection Vasculitis
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.
