Eosinophils Test: Meaning, Normal Range, Low & High Eosinophil Causes, Symptoms, and Complete Medical Guide
What Are Eosinophils?
Eosinophils are a type of white blood cell (WBC) and belong to the granulocyte family. They play an important role in your immune system by fighting parasites, controlling allergic reactions, and regulating inflammation. When stained under a microscope, eosinophils have bright reddish-pink granules, which makes them easy to identify. These granules contain enzymes and chemicals that help them attack invaders that the body considers harmful.
Eosinophils normally exist in small numbers in your bloodstream. Most of them stay in body tissues like the lungs, skin and digestive tract, where they monitor for infections, allergens and inflammation. When the body senses a threat—such as parasites, asthma triggers or allergy-causing substances—eosinophils become active and respond immediately.
Where Are Eosinophils Produced?
Eosinophils are produced in the bone marrow from hematopoietic stem cells, the same cells responsible for forming other white blood cells, red blood cells and platelets. After their development, eosinophils circulate in the bloodstream for a short period—usually less than a day. They then move into tissues where they stay longer and participate in immune responses.
These cells are often found in:
- The skin
- Lungs
- Intestines
- Lymph nodes
- Spleen
Their presence in these areas allows them to respond rapidly when an allergen, parasite or inflammatory signal is detected.
Functions and Importance of Eosinophils
Eosinophils serve several important roles in the immune system. They are especially helpful in fighting parasites and reacting to allergies.
Defending Against Parasites
Eosinophils destroy parasitic worms (helminths) and certain protozoa. Parasites are too large for neutrophils to attack, so eosinophils release toxic proteins and enzymes that damage or kill them.
Allergy Response
They are active in allergic reactions such as asthma, eczema and hay fever. When allergens enter the body, eosinophils release chemicals that contribute to inflammation. Although this helps protect the body, excessive eosinophil activity can worsen allergy symptoms.
Controlling Inflammation
Eosinophils regulate inflammation by releasing substances that either increase or decrease the immune response. This helps the body avoid unnecessary tissue damage.
Releasing Enzymes and Toxins
Their granules contain proteins such as major basic protein and eosinophil cationic protein, which attack parasites and harmful invaders.
Working With Other Immune Cells
Eosinophils interact with mast cells, basophils, antibodies and T lymphocytes to coordinate immune defense. They help activate or balance other immune responses based on the body’s needs.
Without eosinophils, the body would struggle to defend against certain parasites and would not be able to control allergic reactions properly.
Causes of Low Eosinophils (Eosinopenia)
Low eosinophil levels are known as eosinopenia. This condition often reflects the body’s reaction to stress or medication rather than a direct disease of eosinophils.
Corticosteroid Use
Medications like prednisone suppress eosinophil production. Steroids are commonly used for asthma, allergies and autoimmune disorders, which often lowers eosinophil count.
Acute Stress or Trauma
Severe physical stress, injury or surgery can reduce eosinophil levels temporarily.
Cushing’s Syndrome
High cortisol levels in this condition suppress many immune functions, including eosinophils.
Severe Infections
Serious bacterial infections may lower eosinophil counts as the immune system shifts focus to other white blood cells.
Sepsis
Life-threatening infections may drastically reduce eosinophils due to immune exhaustion.
Symptoms of Low Eosinophils
Eosinopenia usually does not cause symptoms on its own. Instead, it may indicate:
- A weakened immune response
- Side effects of steroid medications
- The presence of severe stress or illness
Low eosinophils are generally not harmful unless associated with a serious underlying condition.
Causes of High Eosinophils (Eosinophilia)
High eosinophil levels are known as eosinophilia. This condition occurs when the body reacts strongly to allergens, parasites, inflammation or certain diseases.
Parasitic Infections
Worm infections like roundworms, hookworms, schistosomiasis or protozoa often elevate eosinophil levels.
Allergic Conditions
Common allergy-related causes include:
- Asthma
- Eczema
- Hay fever
- Allergic sinusitis
In allergic conditions, eosinophils release inflammatory chemicals that contribute to symptoms.
Autoimmune Diseases
Conditions such as lupus or rheumatoid arthritis may raise eosinophil levels due to chronic inflammation.
Certain Cancers
Leukemia, lymphoma and other blood cancers can cause eosinophilia.
Drug Reactions
Some medications trigger allergic responses that increase eosinophil counts. These may include:
- Antibiotics
- Non-steroidal anti-inflammatory drugs
- Seizure medicines
Chronic Infections
Long-term infections in the lungs or intestines may also cause eosinophilia.
Hypereosinophilic Syndrome (HES)
A rare disorder where the body produces too many eosinophils, which can damage organs.
Symptoms of High Eosinophils
Symptoms depend on the underlying cause rather than eosinophilia itself. Common symptoms include:
- Wheezing, coughing or shortness of breath (as seen in asthma)
- Itchy skin or rashes (eczema, allergies)
- Abdominal pain, diarrhea or nausea (parasites)
- Fever and fatigue
- Enlarged lymph nodes or spleen in severe cases
These symptoms reflect inflammation or infection rather than eosinophils alone.
Eosinophil Reference Range
Different labs may use slightly different ranges, but typical values are:
Absolute Eosinophil Count (AEC)
- Normal: 0 – 500 cells/µL
Percentage of Total WBCs
- Normal: 1% – 4%
Doctors consider both the absolute value and percentage to understand whether eosinophil levels are abnormal.
Sample Type and Collection
- Sample Required: Whole blood
- Collection Tube: Lavender-top EDTA tube
A blood sample is taken from a vein in the arm. Eosinophil levels are measured automatically as part of a CBC with differential report.
Test Preparation
- No fasting is required.
- Stay hydrated before the test.
- Tell your doctor if you take steroids, allergy medications or immunosuppressants.
- Mention recent symptoms such as asthma, rashes or digestive problems.
When to Consult a Doctor
You should speak with a doctor if:
- You experience frequent allergies, asthma or recurring sinus issues
- You notice unexplained rashes or itchy skin
- Your CBC shows eosinophils consistently high or low
- You experience abdominal discomfort, diarrhea or suspect parasitic infection
- You have fatigue along with swollen lymph nodes or spleen
- You take long-term steroid medications
Early evaluation helps detect allergic reactions, parasitic infections, immune disorders and rare blood conditions.
Important Word Explanations
- Eosinophils: White blood cells with pink granules that help fight parasites and allergies.
- Eosinophilia: High eosinophil count, often due to allergies or parasites.
- Eosinopenia: Low eosinophil count, often caused by steroids or stress.
- Granulocytes: WBCs containing granules (eosinophils, neutrophils, basophils).
- CBC with Differential: A test showing detailed counts of all WBC types.
~END~