What Is an Eosinophil Count?

If you take a blood test and the results aren’t in the normal range, your doctor may recommend more tests to figure out the problem. If this happens on a test called a white blood cell differential, you may need to get another blood test called an absolute eosinophil count. You might also get this test if your doctor thinks you have a particular kind of disease.

An eosinophil count can help diagnose a few conditions. You might have a high count with the following:

  • Eczema (itchy, inflamed skin)
  • Allergic disorders like asthma or hay fever
  • An infection caused by a parasite
  • A reaction to certain medications
  • The early stages of Cushing’s disease, a rare condition that can happen if you have too much of a hormone called cortisol in your blood
  • Acute hypereosinophilic syndrome, another rare condition that’s similar to leukemia and can be life-threatening

What the Test Does

The eosinophil count measures the amount of eosinophils in your blood. They’re a kind of white blood cell that helps fight disease. The exact role of eosinophils in your body isn't clear, but they're usually associated with allergic diseases and certain infections. They're made in your bone marrow and then travel to different tissues.

Your eosinophils do two important things in your immune system: curb infections and boost inflammation, which can help you fight off a disease.

The key is for eosinophils to do their job and then go away. But if instead you have too many eosinophils in your body for a long time, doctors call this eosinophilia, and it can cause chronic inflammation. This can damage tissues. Conditions where there are too many eosinophils are in the body include eosinophilic esophagitis (a disorder in your esophagus) or eosinophilic colitis (in your large intestine). Eosinophilic disorders also can happen in your stomach, small intestine, blood, or other organs. Sometimes, a biopsy will show that you have a high amount of eosinophils in your tissues, but you might not have a high amount in your blood.

How the Test Is Done

If your doctor wants an absolute eosinophil count, you’ll need a blood test. During the test, a health care worker will put a needle into one of your veins and take out some blood.

In a lab, a technician will add a special stain to your blood sample, in order to see the eosinophils and count how many you have in every 100 cells. They’ll multiply that percentage by your white blood cell count to get your absolute eosinophil count.

Generally, a normal test value is less than 350 cells per microliter (cells/mcL). But because this number might not be the same at every lab, you should talk with your doctor to understand your results.

WebMD Medical Reference Reviewed by Arefa Cassoobhoy, MD, MPH on December 17, 2018



UCSF Medical Center: "Eosinophil Count Absolute."

UCLA: "Cushing's Disease."

Mayo Clinic: "Eosinophilia."

Cincinnati Children’s Hospital: "What is an Eosinophilic Disorder?"

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