White blood cells are an important part of your body’s immune system. They’re vital to protecting you from invading bacteria, viruses, and parasites. Your bone marrow produces all five of the different kinds of white blood cells in the body.
Each white blood cell lives anywhere from several hours to several days in the blood stream. An eosinophil is a type of white blood cell. Eosinophils are stored in tissues throughout the body, surviving for up to several weeks. The bone marrow continually replenishes the body’s white blood cell supply.
The number and type of each white blood cell in your body can give doctors a better understanding of your health. Elevated levels of white blood cells in your blood can be an indicator that you have an illness or infection. Elevated levels often mean your body is sending more and more white blood cells to fight off infections.
An eosinophil count is a blood test that measures the quantity of eosinophils in your body. Abnormal eosinophil levels 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. It appears now that nearly every system of the body relies on eosinophils in some way. Two important functions are within your immune system. Eosinophils destroy invading germs like viruses, bacteria, or parasites such as hookworms. They also have a role in the inflammatory response, especially if an allergy is involved.
Inflammation is neither good nor bad. It helps 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 a significant role in the inflammation related to allergies, eczema, and asthma.
Your doctor may discover abnormal eosinophil levels when a white blood count differential is performed. A white blood count differential test is often done alongside a complete blood count (CBC) and determines the percentage of each kind of white blood cell present in your blood. This test will show if you have an abnormally high or low count of white blood cells. White blood cell counts can vary in certain diseases.
Your doctor may also order this test if they suspect specific diseases or conditions, such as:
- an extreme allergic reaction
- a drug reaction
- certain parasitic infections
There are no special preparations necessary for this test. You should inform your doctor if you’re taking any blood-thinning drugs such as warfarin (Coumadin). Your doctor may advise you to stop taking certain medications.
Medications that may cause you to have an increased eosinophil count include:
- diet pills
- interferon, which is a drug that helps treat infection
- some antibiotics
- laxatives that contain psyllium
Before the test, be sure to tell your doctor about any current medications or supplements you’re taking.
A healthcare provider will take a sample of blood from your arm by following these steps:
- First, they’ll clean the site with a swab of antiseptic solution.
- They’ll then insert a needle into your vein and attach a tube to fill with blood.
- After drawing enough blood, they’ll remove the needle and cover the site with a bandage.
- They’ll then send the blood sample to a laboratory for analysis.
In adults, a normal blood sample reading will show fewer than 500 eosinophil cells per microliter of blood. In children, eosinophil levels vary with age.
If you have over 500 eosinophil cells per microliter of blood, then it indicates you have a disorder known as eosinophilia. Eosinophilia is classified as either mild (500–1,500 eosinophil cells per microliter), moderate (1,500 to 5,000 eosinophil cells per microliter), or severe (greater than 5,000 eosinophil cells per microliter). This can be due to any of the following:
- an infection by parasitic worms
- an autoimmune disease
- severe allergic reactions
- seasonal allergies
- leukemia and certain other cancers
- ulcerative colitis
- scarlet fever
- Crohn’s disease
- a significant drug reaction
- an organ transplant rejection
An abnormally low eosinophil count can be the result of intoxication from alcohol or excessive production of cortisol, like in Cushing’s disease. Cortisol is a hormone naturally produced by the body. Low eosinophil counts may also be due to the time of day. Under normal conditions, eosinophil counts are lowest in the morning and highest in the evening.
Unless alcohol abuse or Cushing’s disease is suspected, low levels of eosinophils are not usually of concern unless other white cell counts are also abnormally low. If all white cells counts are low, this can signal a problem with the bone marrow.
An eosinophil count uses a standard blood draw, which you have likely had many times in your life.
As with any blood test, there are minimal risks of experiencing minor bruising at the needle site. In rare cases, the vein may become swollen after blood is drawn. This is called phlebitis. You can treat this condition by applying a warm compress several times each day. If this isn’t effective, you should consult your doctor.
If you have an allergy or parasitic infection, your doctor will prescribe a short-term treatment to alleviate symptoms and revert your white blood cell count to normal.
If your eosinophil count indicates an autoimmune disease, your doctor may want to conduct more tests to determine which type of diseases you have. A wide variety of other conditions can cause high levels of eosinophils, so it’s important to work with your doctor to figure out the cause.