Eosinophils and Understanding Your Count (2024)

Eosinophils are white blood cells that play an essential role in your immune system—specifically in fighting diseases and infections. They also contribute to the body’s immune response during allergic reactions and asthma attacks. When your body detects a threat like harmful pathogens (e.g., parasites, viruses, bacteria) or allergens, your immune system releases eosinophils which migrate to the affected area to destroy the invading cells.

Your eosinophil count can give healthcare providers better insight into whether your body is fighting allergies or infections or if you have an underlying condition, such as an autoimmune disorder.

Eosinophils are specialized white blood cells that serve several important immune functions to help keep you healthy. Eosinophils travel to the body part where an infectious agent (e.g., parasitic worm) is detected. They release toxic chemicals and proteins that can attack and kill harmful cells or germs to prevent illness.

Your eosinophils are also involved in helping fight allergic reactions. If you have allergies and come into contact with an allergen (such as pollen or dust mites), your immune system perceives the allergen as a threat and triggers an allergic response. Eosinophils are central to this response and promote inflammation. This is important because inflammation helps isolate and control the site of the allergic reaction. But, the inflammation can also cause itching, sneezing, and a runny nose.

​Early research also suggests that eosinophils also play a role in healing wounds. Although scientists are still exploring how eosinophils promote healing, some experts believe that eosinophils stimulate the growth of new blood vessels, contribute to creating new tissues, and assist in forming scars.

When you have a balanced eosinophil count, eosinophils help your body fight disease and heal. But high levels of eosinophils can contribute to chronic inflammation and damage healthy tissues, increasing your risk of developing inflammatory conditions such as asthma, atopic dermatitis (eczema), allergic rhinitis, nasal polyps, and eosinophilic esophagitis.

How To Measure Eosinophils

An eosinophil count is a blood test (called the EOS blood test) that measures the number of eosinophils in your bloodstream. Your healthcare provider may order one of the following blood tests if they suspect you have a certain health condition or disease, such as asthma, allergies, or a parasitic infection:

• White blood cell count (WBC) with differential: Measures the amount of each type of white blood cell circulating in your bloodstream.
• Complete blood count (CBC): Measures the different components in your blood, including red blood cells, white blood cells, and blood platelets.
  

During one of these blood tests, a healthcare provider will take a small blood sample and send it in for analysis. To collect your blood sample, your provider 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
  

Once the lab receives your blood sample, a trained lab technician will prepare a blood smear by spreading a thin layer of your blood on a glass slide. They will then examine the slide under a microscope to identify and count your eosinophils, which 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 of blood.

An eosinophil count is the number of eosinophils in your blood. Your count can provide valuable information about your health and help healthcare providers diagnose or monitor certain health conditions that you might have.

The normal range of eosinophils is less than 500 eosinophil cells per microliter (mL) of blood (or, less than 5% of the total white blood cell count). If your eosinophil count falls within the normal range, it generally means that your immune system is functioning normally and there are no apparent signs of allergic reactions, parasitic infections, autoimmune disorders, or other eosinophil-related conditions.

Interpreting your eosinophil count can be complex, so talk to your healthcare provider about your individual 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

When eosinophils are low, you may have a condition called “eosinopenia.” Certain health conditions and medications can cause low eosinophil counts, including:

• Acute bacterial infections
• Excessive alcohol intake
• Using steroids
• Excess production of cortisol (a stress hormone)

If you have low eosinophil counts and the cause is unknown, your healthcare provider may order additional tests to learn why your counts may be too low and provide you with an accurate diagnosis. You may sometimes also require certain treatments to raise your count to a healthy range.

When eosinophils are high, you may have a condition called “eosinophilia.” Eosinophilia is a diagnosis that a provider can give you indicating that you have a high number of eosinophils in your blood. There are three categories of eosinophilia: