What Are Eosinophils—and What Level Indicates Cancer?
Medically reviewed by Archana Sharma, DO
Eosinophils are white blood cells that play an essential role in the immune system, specifically in fighting diseases and infections. A high eosinophil level, for example, can indicate a range of several health conditions, from allergic reactions and asthma to certain cancers.
These cells also contribute to the body's immune response during allergic reactions and asthma attacks. The immune system releases eosinophils when the body detects harmful pathogens—such as parasites, viruses, or bacteria—and allergens. Eosinophils migrate to the affected area to destroy the invading cells.
Whether your level of eosinophils is high or low, the count can give healthcare providers better insight into your immune system responses. Here's what you need to know.
Related: Understanding MCHC Blood Test Results
What Are Eosinophils?
Eosinophils are specialized white blood cells that serve several important immune functions to help keep you healthy. These cells travel to the body part where an infectious agent is detected. They release toxic chemicals and proteins that can attack and kill harmful cells or germs to prevent illness.
How Are They Helpful?
Eosinophils are also involved in helping fight allergic reactions. The immune system perceives an allergen as a threat and triggers an allergic response. Eosinophils are central to this response and promote inflammation. Inflammation helps isolate and control the site of the allergic reaction and can cause itching, sneezing, and a runny nose.
Research has shown that eosinophils play a role in healing wounds. Scientists are still exploring how eosinophils promote healing.
Some experts believe that eosinophils:
Assist in forming scars
Contribute to creating new tissues
Stimulate the growth of new blood vessels
How To Measure Eosinophils
An eosinophil count is part of a complete blood count (CBC). A CBC measures the different components in your blood, including eosinophils, red blood cells, white blood cells, and blood platelets.
A healthcare provider will take a small blood sample and send it in for analysis. To collect your blood sample, they will:
Look for a vein to collect blood from, usually on the inside of your elbow.
Clean the area with an antiseptic and tie an elastic band around your arm to make it easier to collect the blood sample.
Gently insert the needle into your arm and collect the blood in a tube (vial).
Remove the needle and place a bandage on your arm to prevent bleeding.
A trained lab technician will then prepare a blood smear by spreading a thin layer of your blood on a glass slide. They will examine the slide under a microscope to identify and count your eosinophils. These cells look like small, orange-colored particles or spots.
A lab technician can determine your eosinophil count by multiplying the percentage of eosinophils per 100 cells by the total white blood cell count in your body. The absolute eosinophil count represents the actual number of eosinophils per microliter (µL) of blood.
Understanding Levels
An eosinophil count is the number of eosinophils in your blood. Your count can provide valuable information about your health and help diagnose or monitor certain health conditions that you might have.
The normal range of eosinophils is less than 500 eosinophil cells per µL of blood, or less than 5% of the total white blood cell count. Your immune system is generally functioning normally if your eosinophil count falls within the normal range. There are also no apparent signs of eosinophil-related conditions with this result.
Interpreting your eosinophil count can be complex. Talk to a healthcare provider about your results. They can answer your questions, discuss your results, and offer recommendations and guidance on the next steps if your results are outside the normal range.
Low Eosinophil Count
You may have a condition called "eosinopenia" if your levels are low. Certain health conditions and medications can cause low eosinophil counts, including:
Acute bacterial infections
Excess alcohol intake
Excess production of cortisol (a stress hormone)
A low eosinophil count may have an unknown cause. A healthcare provider may order additional tests to learn why your counts are low and provide you with an accurate diagnosis. You might sometimes also require treatments to raise your count to a healthy range.
High Eosinophil Count
You may have a condition called "eosinophilia" if your levels are high. There are three categories of eosinophilia:
Category | Count |
Mild | 500 to 1,000 eosinophils per µL of blood |
Moderate | 1,000 to 5,000 eosinophils per µL of blood |
Severe | More than 5,000 eosinophils per µL of blood |
Many conditions can cause eosinophilia, including:
Allergic reactions
Asthma
Atopic dermatitis (eczema)
Certain cancers (e.g., leukemia, Hodgkin's lymphoma)
Drug reactions
Esophagitis
Gastroenteritis
Inflammatory bowel disease (IBD)
Parasitic infections
It's important to note that eosinophilia does not cause symptoms on its own. Any symptoms will likely be a result of the infection or condition causing your high eosinophil count. It's still important to treat eosinophilia. A high eosinophil count can damage any vital organ, including the heart, lungs, skin, intestines, and stomach if left untreated.
How To Treat Eosinophilia
Treatment will focus on managing the specific condition causing eosinophilia. This may include medications, lifestyle changes (e.g., avoiding certain foods), or using an inhaler. A healthcare provider may recommend general treatments to lower your count and prevent complications from occurring for unknown causes.
This usually includes using drugs for treatment, which may include:
Drug Class | Brand Name | Generic Name |
Leukeran | Chlorambucil | |
Glucocorticosteroids | Rayos | Prednisone |
Immunomodulators | Intron-A | Interferon-alpha |
Monoclonal antibodies | Nucala | Mepolizumab |
Tyrosine kinase inhibitors | Gleevec | Imatinib |
Related: What Is a Chloride Blood Test?
A Quick Review
Eosinophils are a type of white blood cell involved in the body's immune response. An eosinophil count blood test measures the number of eosinophils circulating in your bloodstream and provides important information about your health.
High eosinophil levels (eosinophilia) can occur due to various conditions, like allergies or certain cancers. Low eosinophil levels (eosinopenia) may indicate conditions like an acute bacterial infection or hormonal balance. Talk to a healthcare provider about your results to learn the causes and receive a treatment plan.
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