Eosinophils are white blood cells that help fight off infections, but they can sometimes cause allergic conditions. They belong to a group of white blood cells called granulocytes.
Granulocytes contain tiny particles (granules) to fight off germs like parasites. But the chemicals inside these granules also trigger other immune cells to protect you against allergens, toxins, and other infections.
In particular, mast cells often aid eosinophils to do two key things which can help you fight off diseases:
- Boost inflammation
- Curb infections
Because eosinophils are made in your bone marrow, so very few live in your bloodstream. To fight off an infection or an allergen, your body makes more eosinophils. These higher levels can travel to different parts of your body for protection.
If the eosinophils stay around, the higher levels can cause tissue damage and other problems. Your doctor can order a blood test to check your eosinophil levels. Higher of lower eosinophil levels can give your doctor more information about your infection, allergies, and more.
What Is an Eosinophil Count?
An eosinophil count is a blood test that measures the number of eosinophils in your blood. Your doctor can check your eosinophil levels using a blood test called a complete blood count (CBC) with a differential.
Your eosinophil levels get measured one of two ways:
- Absolute eosinophil count (AEC), the number of eosinophils in 1 microliter (µL) of your blood
- Percentage of all your white blood cells (not as reliable)
Absolute eosinophil count is the most trusted way to count the number of eosinophils under the microscope. If your blood test numbers aren't in range, your doctor may suggest more tests to figure out the problem.
How the Test Is Done
It depends on how the lab measures eosinophils. Usually, to get the absolute eosinophil count:
- A technician in the lab prepares your blood sample.
- They add a special fluid to the blood sample to stain your eosinophils.
- The dye causes the granules to glow in a reddish color.
- A technician counts how many glowing eosinophils are in 1 µL of your blood
Some labs measure the eosinophil count as a portion (percentage) of all your white blood cells. It's sometimes called a blood differential test, which means a technician:
- Adds a special red-colored stain to the blood sample, which helps the eosinophils glow under the microscope
- Counts the number of eosinophils out of every 100 cells (which gives the eosinophil percentage)
- Multiplies the eosinophil percentage by your total white blood cell count
Both methods can give you an eosinophil count, but most experts trust the AEC test the most.
What Do the Test Results Mean?
An eosinophil count can't diagnose any specific condition, but the test can help guide next steps. The number of eosinophils in your blood usually make up less than 5% of your total blood cells. Certain medical conditions, infections, or allergens can raise or lower these levels.
Higher eosinophil counts can point your doctor in the right direction they may:
- Order more tests for allergies, infections, or another problem
- Confirm if certain treatments are working
- Order testing to check for lung problems
Because there are different ways to measure eosinophils, the count can be a bit different between laboratories.
What Does a High Eosinophil Count Mean?
The key is for eosinophils to do their job and then go away. For most people, one high eosinophil count doesn't mean anything. That's especially true if the next test goes back to normal.
Instead, your doctor looks for eosinophil levels that are very high or remain high over time. This can help guide your treatment and testing. Eosinophils can stay high for many reasons, so tell your doctor if you take any medications or have:
- Autoimmune conditions
- Eczema (allergic skin condition)
- Other allergic conditions
- An infection
Other test for eosinophils
Sometimes, your eosinophils can travel from your bloodstream into your tissues and organs. If this happens, you might not have high levels of eosinophils in your blood. Your doctor may do a biopsy to test the eosinophil levels in a small piece of tissue.
What Is Eosinophilia?
Eosinophilia means that you have too many eosinophils in your body. The absolute eosinophil count can tell your doctor about your levels. These white cells normally collect inside certain tissues to protect your body from allergens and infections.
With eosinophilia, the high levels of eosinophils stay around. An allergic reaction, such as to a medicine, commonly causes this condition. You may have eosinophilia if you get tested at least two weeks apart and both tests show an eosinophil count of 500 or more in 1 uL of blood.
Types of eosinophilia
The three main types of eosinophilia are:
- Primary, which is linked to blood cancers (leukemias and myeloproliferative neoplasms)
- Secondary, which is usually linked to allergies, infections, or autoimmune problems
- Idiopathic, which means the cause isn't known or there are other reasons
Most common type of eosinophilia
An allergic condition is one of the most common reasons for eosinophilia — mild-to-moderate elevations. The eosinophil count can help support more testing to diagnose many allergic conditions, especially eosinophilic disorders.
Eosinophilic disorders are caused by too many eosinophils traveling to an area in your body and damaging the nearby tissues and organs.
Absolute eosinophil count ranges
| Level of Eosinophilia | Absolute Eosinophil Count Range | Medical Conditions |
|---|---|---|
| Eosinopenia (low levels of eosinophils) | Under 100 eosinophils in 1 µL of blood (< 0.1 × 103 per µL) |
|
| Normal range | 100-500 eosinophils in 1 µL of blood (0.1 to 0.5 × 103 per µL) | |
| Mild eosinophilia | 500-1,500 eosinophils in 1 µL of blood (0.5 to 1.5 × 103 per µL) |
|
| Moderate eosinophilia | 1,500-5,000 eosinophils in 1 µL of blood (1.5 to 5 × 103 per µL) |
|
| Severe eosinophilia | Above 5,000 eosinophils in 1 µL of blood (> 5 × 103 per µL) |
|
What Does a Low Eosinophil Count Mean?
Some medical condtions can lower your eosinophil levels. If your eosinophil count is too low, it's called eosinopenia. There are many reasons for low eosinophil levels, such as:
- Your immune system might be dampened from an infection (sepsis).
- You may be taking steroids as a treatment for another medical condition.
- Your body may have too much of a hormone called cortisol, or Cushing's syndrome.
A low eosinophil count usually doesn't cause a problem. That's because another part of your immune system usually steps up to help. Once you stop taking steroids or get treatment, your eosinphil count will likely go back up.
The Role of Eosinophils in Allergies and Asthma
Eosinophils can move into your airways and lungs to protect your body from allergens. Asthma and allergies happen when your airways and lung tissues get inflamed. Sometimes this inflammation starts after too many eosinophils travel to your lungs.
These immune cells can release four types of toxic proteins, which may swell and inflame your airways:
- Major basic protein
- Eosinophil cationic protein
- Eosinophil-derived neurotoxin
- Eosinophil peroxidase
You may not have symptoms if your eosinophils are mildly high. In fact, many people with allergic conditions have higher eosinophil levels without knowing it.
What is eosinophilic asthma?
If you have too many eosinophils in your airways that cause swelling, inflammation, and tissue damage, it's called:
- Eosinophilic asthma
- Eos asthma
- E-asthma
Only about 5%-10% of people in the U.S. have this type of asthma. Eosinophils can get into your lungs and break down to form Charcot-Leyden crystals. If your doctor suspects e-asthma, they can check your sputum for these crystals.
Eosinophils and Other Medical Conditions
Your doctor will look at how high your eosinophils levels get and how long they stay that way. This helps them match your clinical signs and other tests to check for common reasons for eosinophilia, such as:
- Medication reactions
- Infections from worm-like parasites
- Certain cancers, including blood cancers and solid tumors
Hypereosinophilic syndromes
Most people have 500 or fewer eosinophils in 1 μL of blood. But with hypereosinophilic syndromes (HES), you can get 1,500 or more eosinophils in 1 μL of blood. It's rare, but if your eosinophils stay high, HES can cause tissue and organ damage in your:
- Heart
- Lungs
- Skin
- Throat
- Nerves and brain
This group of rare white cell disorders can include:
- Lymphocytic HES
- Myeloid HES
- Associated HES (often caused by medications or parasites)
- Idiopathic HES (unknown cause)
- Overlap HES (includes conditions such as eosinophilic granulomatosis with polyangiitis)
You and your doctor will go over the best treatment plan for your HES, including steroids, biologic medications, and other options.
When to call the doctor
Eosinophils can lead to a serious allergic reaction. Go to the nearest emergency room to get medical help if you have signs of anaphylaxis, including:
- Fever (100 F or above)
- Rash
- Trouble breathing or shortness of breath
- Infection (especially in your lungs)
- Swelling in your face
- Swollen lymph nodes, spleen, or liver
Next Steps
Your doctor will first find and treat the codition that is raising your eosinophil levels. If needed, your doctor can do more testing to figure out where the eosinophils are located inside your tissues, such as:
- Chest X-rays
- Liver function test
- Stool samples
- Biopsy
- Urine test
You and your doctor will review all the tests, along with your medical history. This helps you make better treatment decisions about your eosinophilia, eosinophilic disorder, or related conditions.
Takeaways
The absolute eosinophil count (AEC) tells you how many eosinophils are in 1 microliter of blood. These white blood cells protect you against infections, allergens, and toxins. Out-of-range counts point to more testing for allergic conditions, parasites, blood cancers, and eosinophilic disorders. These disorders cause too many eosinophils to build up in your body, which can lead to tissue and organ damage. Some conditions can trigger anaphylaxis, a life-threatening allergic reaction. So get medical care right away if you have signs of a fever, rash, problems breathing, or swelling in your face, lymph nodes, spleen, or liver.
FAQs About Eosinophils
Do I need to fast before an absolute eosinophil count test?
No, you don't need to do anything special before this blood test. Just let the person know if you've eaten or had anything to drink before they take your blood. Some doctors and labs just like to know that information.
Can medications cause a false high or low eosinophil count?
Yes, there are many reasons for low or high eosinophil levels, including medications. You can have higher levels if you have an autoimmune condition, eczema, or certain types of blood cancers. So, let your doctor know if you have taken:
- Anti-seizure medications such as carbamazepine (Carbatrol, Epitol, Equetro, Tegretol, and Tegretol XR, ) or lamotrigine (Lamictal/CD/ODT/XR and )
- Allopurinol (Aloprim, Lopurin, and Zyloprim)
- Antibiotics such as sulfamethoxazole/trimethoprim (Bactrim, Septra, and Sulfatrim) and vancomycin (Firvanq Kit, Vancocin, and others)
Although rare, an allergic reaction to medication can happen, which can be life-threatening. Get emergency medical care right away if you have a fever, rash, swelling in your face, or a hard time breathing.
Can medications cause really high eosinophil counts?
It's rare, but some medications can cause a severe allergic reaction known as drug reaction with eosinophilia and systemic symptoms (DRESS). This allergic reaction can be life-threatening, so get medical help right away. Go to the nearest emergency room if you have:
- Fever (100 F or more)
- Weakness or malaise
- Rash (flat, red, and wide-spread usually on your upper chest or face)
- Swelling in your face
- Enlarged lymph nodes
- Swelling or congestion in your nose and throat
Why do eosinophil counts vary throughout the day?
Your eosinophil counts are lowest in the morning but higher at night. That's because eosinophil levels change in the opposite direction to cortisol levels, a hormone. Because cortisol levels move up and down throughout the day, your eosinophils also move.
Can stress or exercise affect my eosinophil levels?
Yes, stress and exercise can lower your eosinophil levels. Lower eosinophils can also be caused by taking beta-blockers or steroids or because of an infection.
