Eosinophils are a type of white blood cell that fight bacterial and viral infections. High eosinophil levels can indicate a reaction to infection, cancer, or allergens. Low levels may be due to alcohol intoxication or indicate an underlying hormone disorder.

Medical professionals may measure a person’s eosinophil levels as part of a white blood count. This may form part of a complete blood count.

In this article, we cover what people can expect from their eosinophil count test, as well as what the test results may mean.

Close-up of a scientist picking a medical sample test tube from the rackShare on Pinterest
alvarez/Getty Images

An eosinophil count is the number of eosinophils in the body. Eosinophils, a type of white blood cell, help fight off bacterial and viral infections.

A person may require an eosinophil count blood test if they show signs of certain infections or allergic reactions. Doctors may recommend the eosinophil test if someone has abnormal results from another blood test.

The test itself does not typically require preparation. However, people should tell their doctor if they take any medications, as they might affect the results.

People having other blood tests at the same time may need to avoid eating for a period before the test. A doctor can provide specific advice on this.

An eosinophil count blood test is similar to other blood tests.

  • A healthcare professional will prepare the skin by swabbing it with antiseptic, and they may put an elastic band around the arm to make the vein more prominent.
  • They will then insert the needle into the vein. The healthcare professional will usually draw the blood from a vein over the front of the elbow area.
  • Once they have collected enough blood, they will remove the needle and elastic band before using a cotton swab or a bandage to stop any bleeding.

The entire process is quick, taking only a few minutes. Some people may feel dizzy or nauseous at the sight of the blood, or they may have mild bruising around the draw site for a few days after the test.

A laboratory technician will stain the sample to highlight the eosinophils and other blood cells, and they will then count the number present under a microscope to give a result.

After assessing blood samples, the laboratory technician will send the results to the doctor or directly to the person. The results will indicate whether a person’s eosinophil levels are within or outside normal ranges.

Normal levels

For adults, a normal eosinophil count is up to 450-500 cells per cubic millimeters (cells/mm3) in the blood.

Different laboratories may, however, have different normal reference ranges. A person should ask a doctor to explain the results if there is any confusion.

High eosinophil count

Having a higher-than-normal eosinophil count in the bloodstream is called eosinophilia.

Medical professionals divide high eosinophil levels into three brackets:

  • mild (500–1,500 cells/mm3)
  • moderate (1,500–5,000 cells/mm3)
  • severe (greater than 5,000 cells/mm3)

People may have a high eosinophil count if they have:

Low eosinophil count

Healthcare professionals often define a low eosinophil count as less than 30 cells/mm3. Low eosinophil counts may result from:

  • Alcohol misuse: Alcohol misuse can cause the levels of eosinophils and other white blood cells to drop, which reduces the body’s immune system response to infections and other disease states.
  • Overproduction of cortisol: Excess levels of cortisol, which is a glucocorticosteroid hormone, may have links to a lower eosinophil count and lower immune function. People with Cushing’s syndrome overproduce cortisol.
  • Infection reaction: Bloodstream infections, such as sepsis, can lower the amount of circulating eosinophils.
  • Corticosteroids: These medications can reduce immune function, which in turn can lead to lower eosinophil levels.

Abnormal results indicate that the eosinophil count is too high or too low. Below, we break down what these results might mean.

Complications of high eosinophil levels

Mild eosinophilia does not often cause symptoms.

However, severe eosinophilia can lead to organ damage without prompt treatment. This can be fatal in the most severe instances.

In rare cases, high eosinophil levels can indicate severe infection or the presence of certain cancers.

Complications of low eosinophil levels

Typically, low eosinophil levels are not cause for concern. Other parts of the immune system can often compensate for a drop in eosinophils. If a person has a lower-than-normal eosinophil count but no cortisol production issues or excessive alcohol exposure, a doctor may look at other different white blood cell counts.

It is not usually a cause for concern if these are normal.

What comes next for people with high or low eosinophil counts depends on the underlying cause. A doctor may need to carry out further testing to determine the reason for an abnormal result.

People who have an infection or allergy that is causing eosinophilia can take medications to help resolve the issue and allow the restoration of normal eosinophil levels.

People with autoimmune diseases or other medical conditions may require a more comprehensive treatment, including immunosuppressive medications and lifestyle changes.