Patient education: Eosinophil count (The Basics)

What is an eosinophil count? — This is a type of blood test that tells you how many eosinophils you have. Eosinophils are a type of white blood cell. They help your immune system, or infection-fighting system, work the way it should.

●If you have too many eosinophils, there are many possible causes. Some are mild, and some are more serious. It can be a sign of certain problems with the lungs, sinuses, skin, or digestive system. Allergies, parasitic infections, certain medicines, and rare cancers can also cause too many eosinophils.

●If you have too few eosinophils, there are several possible causes. It could be related to fever or a viral or bacterial infection. Steroid medicines can also cause too few eosinophils.

Many other things can cause a high or low eosinophil count, too.

An eosinophil count is done as part of a "white blood cell differential" or "complete blood count with differential." This is a test that looks at other parts of the blood, too.

Why might I get an eosinophil count? — Your doctor might order this test:

●As part of a routine checkup

●To see if your eosinophil count is changing over time

●If you have symptoms of a health problem that could cause a high or low eosinophil count

How do I prepare for an eosinophil count? — For this test, you need to get a "blood draw." Your doctor or nurse will tell you where to go for this.

It might help to wear a short-sleeve shirt to your blood draw appointment. This makes it easier for the person drawing your blood to get to your arm.

What happens during a blood draw? — For the blood draw, a needle is used to take a small amount of blood from your arm (figure 1). Collecting the blood only takes a few minutes. The blood is then tested in a lab.

Tell the person who takes your blood:

●If you take "blood thinner" medicines or if you have a bleeding problem – They will make sure that your bleeding is under control before you leave.

●If you have a latex allergy – Some of the supplies used for blood draws might contain latex.

●If you have a preferred arm to use

Getting blood taken does not usually cause problems. You might have a little soreness or bruising where the needle went in.

What do my results mean? — Your doctor or nurse will tell you when to expect your results, and will contact you with the results. Or if you use an online "patient portal," you might get an alert there when your results are ready.

If your eosinophil count is abnormal, your doctor or nurse will talk to you about what to do next. They might need to do more tests to figure out what the cause is.

If you do have a health problem, your doctor will work with you to come up with a plan for treatment.

More on this topic

Patient education: Eosinophilic esophagitis (The Basics)
Patient education: Drug allergy (The Basics)
Patient education: Asthma in adults (The Basics)
Patient education: Asthma in children (The Basics)
Patient education: White blood cell differential (The Basics)
Patient education: Complete blood count (CBC) (The Basics)