What Is Eosinophils In Blood Test


Eosinophils are a type of white blood cell that plays an important part in the immunological response of the body. They get their name from the unique granules within their cytoplasm that stain red-orange when dyed, giving them their distinguishing appearance. Eosinophils account for a modest proportion of overall white blood cell count, typically ranging from 1 to 6%.

Eosinophils play an important role in allergy reactions and immunological responses against parasites. When the body is exposed to an allergen or a parasite infection, eosinophils are drawn to the affected area. They release molecules from their granules that assist in regulating the inflammatory response, including as histamine, leukotrienes, and cytokines.

Eosinophils also play a function in immune response modulation by interacting with other immune cells. They can create and release cytokines, impacting the behaviour of other immune system cells such as T cells and mast cells.

Eosinophils are an important component of the immune system because they control inflammation and interact with other immune cells. Monitoring eosinophil levels can help diagnose and manage certain diseases and ailments.

Eosinophils Count

An eosinophil count measures the number of eosinophils in the blood. Eosinophils are a type of white blood cell that aids in the body’s immune response, particularly during allergic reactions and parasite infections.

A complete blood count (CBC) test, which provides information about the many types of blood cells, is commonly used to determine the eosinophil count. Normal eosinophil counts range from 0 and 500 eosinophils per microliter of blood. 

Eosinophilia, or elevated eosinophil counts, may suggest an allergic illness, asthma, certain autoimmune diseases, or parasitic infections. Low eosinophil numbers, on the other hand, may be linked to specific drugs, hormonal abnormalities, or bone marrow problems. The eosinophil count should be interpreted in conjunction with other clinical data to ascertain the underlying cause and, if necessary, guide further care.

Production Of White Blood Cells

The formation of white blood cells, also known as leukopoiesis, is an important process in the bone marrow. It entails developing and maturing several types of white blood cells, such as neutrophils, lymphocytes, monocytes, eosinophils, and basophils. The process is strictly managed to maintain a balance of different types of white blood cells and a healthy immune system. Cytokines, growth factors, and hormones are all involved in promoting and controlling white blood cell development. Any interruptions or anomalies in this process can result in immune system problems and a reduced ability to fight infections and illnesses.

Why Is An Eosinophil Count Needed?

There are several reasons why an eosinophil count may be needed:

Allergic conditions: Allergic reactions involve eosinophils; hence a high eosinophil count can indicate an allergic illness such as asthma, hay fever, or atopic dermatitis.

Parasitic infections: Eosinophils aid in the battle against parasitic infections, and an elevated eosinophil count may indicate the existence of such an illness.

Autoimmune diseases: Elevated eosinophil counts are related to autoimmune illnesses, such as eosinophilic granulomatosis with polyangiitis (previously known as Churg-Strauss syndrome).

Evaluating treatment response: Monitoring eosinophil levels can aid in assessing the response to treatment for allergic disorders or parasitic infections.

Monitoring disease progression: Tracking eosinophil levels can provide information about disease activity and guide treatment decisions in certain conditions, such as eosinophilic esophagitis or eosinophilic asthma.

Assessing drug reactions: Eosinophilia is a side effect of some drugs, and monitoring eosinophil counts can help identify and control drug-induced responses.

Investigating other conditions: Eosinophil counts may be sought as part of a larger diagnostic workup to evaluate unexplained symptoms or aberrant blood cell counts.

Process Of Eosinophil Test

An eosinophil count is acquired through a simple lab test on a blood sample. Drawing the blood from the patient is the first step. Typically, a healthcare expert may clean the region with an antiseptic, apply a tourniquet to make the veins more apparent, and put a needle into a vein, usually in the arm, to collect blood. A sterile tube is used to collect the blood sample.

After that, the blood sample is transported to a laboratory for analysis. The sample is centrifuged in the lab, where it is spun at high speed to separate the various components of the blood. This distinguishes between red blood cells, white blood cells, and plasma.

Under a microscope, a professional laboratory technician or pathologist will analyse the stained blood smear. They will count and visually determine the number of eosinophils present. The eosinophil count is usually expressed as a proportion of the total number of white blood cells measured.

The eosinophil test findings are sent to the healthcare physician who requested the test. The healthcare provider will interpret the results in light of the patient’s medical history, symptoms, and other diagnostic tests to establish whether the eosinophil count is within the normal range or whether there is an abnormal increase or reduction.

If the eosinophil count is abnormal, more testing and examination may be required to discover the underlying cause. Additional blood tests, imaging investigations, or visits with specialists may be required. The treatment plan will be determined by the specific ailment or underlying cause that has been diagnosed.

Results Interpretation

Within a week, the laboratory technician will submit the findings of your eosinophil test. Your healthcare professional will review the results and inform you of them.

It is normal for the eosinophil blood counts to vary on different days and at different times of day and should not be a cause for concern.

Normal Eosinophil Range 

An absolute eosinophil count of 0 to 500 cells per microliter (0.5 x 109/L) is considered normal. This accounts for less than 5% of total white blood cells.

Normal reference ranges may change between laboratories. If you have any questions, your healthcare professional can clarify your results. 

High Eosinophil Levels

Eosinophilia is defined as an eosinophil count that is higher than normal. Eosinophilia high levels can range between mild to severe:

Mild: 500–1,500 eosinophils per microliter of blood

Moderate: 1 to 5,000 eosinophil cells per microliter of blood is considered moderate.

Severe: 5,000 or more eosinophil cells per microliter of blood is considered severe.

High eosinophil levels could be due to:

  • Allergies (food, environmental)
  • Eczema
  • Asthma
  • Drug hypersensitivity
  • Infections caused by bacteria, viruses, and parasites
  • Autoimmune conditions
  • Vasculitis
  • Adrenal gland dysfunction 
  • Hypereosinophilic syndromes are a set of illnesses characterized by high eosinophil levels and eosinophilia-related organ damage.

The following forms of cancer can cause high eosinophilia:

  • Adult T-cell leukemia/lymphoma, chronic myeloid leukemia, and eosinophilic leukemia are all types of leukemia.
  • Non-Hodgkin’s lymphoma and Hodgkin’s lymphoma
  • Cancer of the colon
  • Cancer of the ovaries
  • Cancer of the lungs

The precise EOS level that may be associated with cancer is dependent upon the type of disease and the individual affected. Eosinophil counts can range from mildly to highly elevated.

Your doctor will request additional tests to confirm your diagnosis, which will guide your therapy.

Low Eosinophil Levels

In healthy adults, eosinophils are generally low. Certain medical problems and drugs, on the other hand, may reduce eosinophil levels.

Corticosteroids and other immune system suppression drugs can diminish eosinophil production and function.

Cushing’s syndrome develops when the body produces too much cortisol (stress hormone) over time. Cortisol levels that are too high depress the immune system and may lower eosinophil numbers.

Lower eosinophil levels can be caused by sepsis, the body’s severe response to an acute bacterial or viral infection. This potentially fatal disorder disrupts the cytokines that govern eosinophil production.

Heavy alcohol consumption reduces the number of white blood cells in general; thus it may reduce the number of eosinophils as well.

If you have low eosinophil numbers and symptoms of an underlying health condition, your doctor will order more tests to make an accurate diagnosis. 


Eosinophils are white blood cells that specialize in fighting infection. Your doctor may conduct an Eosinophils blood test to determine the number of eosinophils in your bloodstream. This could be to look into the reason for particular symptoms like diarrhoea, fever, or rash. It could also aid in diagnosing a suspected illness, such as asthma, an infection, or some malignancies. Medication for the underlying cause of eosinophilia usually brings eosinophil levels back to normal.

Frequently Asked Questions

Are there any physical signs of having a high eosinophil count?

Mild eosinophilia (fewer than 1,500 eosinophil cells per microliter of blood) is usually asymptomatic.Eosinophilia can cause asthma, diarrhoea, itching, rash, and a runny nose. If an illness causes your high eosinophil levels, you may experience symptoms of that disease.

Can stress cause an increase in eosinophils?

High eosinophil levels are unrelated to stress. Indeed, stress may lower eosinophil levels. High-stress events cause the body to produce more cortisol (the stress hormone), which can result in a large drop in eosinophil levels.

Is an Eosinophils Test painful?

You may feel a small pinch or sting when the needle is inserted and removed from your skin. Tenderness at the prick site may also occur for a few hours after the blood is drawn.

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