Eosinophils: What are they? Propóstio, Preparation, Procedure, Results and Complications

White blood cells are an essential part of the body’s immune system.

They are vital to protect it from the invasion of bacteria, viruses, and parasites. The bone marrow produces the five different types of white blood cells in the body. Each white blood cell lives from several hours to several days in the bloodstream.

What is an eosinophil?

An eosinophil is a type of white blood cell stored in tissues throughout the body and survived for several weeks. The bone marrow continually replenishes the body’s supply of white blood cells.

The number and type of each white blood cell in your body can give doctors a better understanding of your health. The elevated levels of white blood cells in your blood can indicate that you have a disease or infection.

Elevated levels often mean that your body is sending more white blood cells to fight infections.

An eosinophil count is a blood test that measures the number of eosinophils in your body. Abnormal levels of eosinophils are often discovered as part of a routine complete blood count (CBC) test.

Ongoing research continues to uncover an expanding list of roles performed by eosinophils. Now it seems that almost all body systems depend on eosinophils somehow.


Two essential functions are inside your immune system. Eosinophils destroy invading germs such as viruses, bacteria, or parasites, such as hookworms, and also have a role in the inflammatory response, especially if it is an allergy.

The inflammation is neither good nor bad. It helps to isolate and control the immune response at the site of an infection, but a side effect is tissue damage around it.

Allergies are immune responses that often involve chronic inflammation. Eosinophils play an important role in inflammation related to allergies, eczema, and asthma.


Why do I need an eosinophil count?

Your doctor may discover abnormal levels of eosinophils when a white blood cell count is performed. A differential test of white blood cell count is often performed along with a complete blood count (CBC) and determines the percentage of each type of white blood cell present in the blood.

This test will show if you have an abnormally high or low white blood cell count. White blood cell counts may vary in certain diseases.

Your doctor may also order this test if you suspect diseases or specific conditions, such as:

  • An extreme allergic reaction
  • A reaction to medications.
  • Certain parasitic infections.


There are no special preparations necessary for this test. You should inform your doctor if you take blood-thinning medications such as warfarin (Coumadin). Your doctor may advise you to stop taking certain medications.

Medications that can cause an increase in eosinophil count include:

  • Diet pills
  • Interferon is a medication that helps treat the infection.
  • Some antibiotics
  • Laxatives that contain psyllium.
  • Tranquilizers

Before the test, tell your doctor about any medication or supplement you are taking.


Your doctor will take a blood sample from your arm by following these steps:

  • First, they will clean the site with an antiseptic solution.
  • Then they will insert a needle into your vein and connect a tube to fill it with blood.
  • After extracting enough blood, they will remove the hand and cover the site with a bandage.
  • Next, they will send the blood sample to a laboratory for analysis.


Expected results: In adults, a regular blood sample reading will show less than 500 eosinophil cells per microliter of blood. In children, eosinophil levels vary with age.

Abnormal results: If you have more than 500 eosinophilic cells per microliter of blood, you indicate that you have a condition known as eosinophilia.

Eosinophilia is classified as mild (500 to 1,500 eosinophilic cells per microliter), moderate (1,500 to 5,000 eosinophilic cells per microliter), or severe (more than 5,000 eosinophilic cells per microliter). This may be due to any of the following causes:

  • Infection by parasitic worms.
  • An autoimmune disease
  • Severe allergic reactions.
  • Eczema.
  • Asthma.
  • Seasonal allergies
  • Leukemia and certain other cancers.
  • Ulcerative colitis
  • Scarlet fever.
  • Lupus.
  • Crohn’s disease.
  • A significant pharmacological response.
  • Rejection of organ transplantation.

An abnormally low eosinophil count may result from alcohol poisoning or excessive production of cortisol, as in Cushing’s disease. Cortisol is a hormone produced naturally by the body.

Low eosinophil counts may also be due to the time of day. Under normal conditions, eosinophil counts are lower in the morning and higher at night.

Unless alcohol abuse or Cushing’s disease is suspected, low levels of eosinophils are usually not a concern unless other white blood cell counts are also abnormally low. If all white blood cell counts are joint, this may indicate a problem with the bone marrow.


An eosinophil count uses a standard blood draw, which you probably have had many times.

There are minimal risks of experiencing mild bruising at the needle site as with any blood test. In rare cases, the vein may swell after blood is drawn. This is called phlebitis; you can treat this condition by applying a warm compress several times a day. If this is not effective, you should consult your doctor.

Excessive bleeding can be a problem if you have a bleeding disorder or take blood-thinning medications, such as warfarin or aspirin. This requires immediate medical attention.

What happens after an eosinophil count?

If you have an allergy or parasitic infection, your doctor will prescribe a short-term treatment to relieve the symptoms and reverse the white blood cell count to normal.

If the eosinophil count indicates an autoimmune disease, your doctor may want to perform more tests to determine what type of disease you have. A wide variety of other conditions can cause elevated levels of eosinophils, so you must work with your doctor to discover the cause.