Eosinophil Count

The eosinophil count is a component of a complete blood count (CBC) that serves as a valuable indicator of immune system function and overall health. 

Eosinophils, a type of white blood cell, play a crucial role in the body's response to allergens, parasites, and certain infections. Understanding the significance of eosinophil count can provide valuable insights into various medical conditions, ranging from allergies and asthma to autoimmune diseases and parasitic infections. 

This article explores the clinical applications of eosinophil count, covering its definition, testing procedure, interpretation, and implications for health. By delving into the factors influencing eosinophil count and strategies for managing abnormal results, this resource offers comprehensive insights into the role of eosinophils in health assessment and disease diagnosis.

Understanding Eosinophil Count

Definition: What is Eosinophil Count?

Eosinophil count refers to the measurement of the number of eosinophils, a type of white blood cell, present in a person's bloodstream. Eosinophils play a crucial role in the immune system's response to allergens, parasites, and certain infections. 

Eosinophils are a type of white blood cell named granulocytes, so called because they contain granules.  The granules contain a variety of chemicals that, when released, stimulate an immune response.  

Eosinophils are particularly important in combating parasitic infections and modulating allergic reactions through the release of cytokines and cytotoxic granules. 

Eosinophils primarily localize within the tissues of the respiratory and gastrointestinal tracts. They have a lifespan of approximately 8 to 12 days.  

In healthy individuals eosinophils constitute less than 5% of circulating leukocytes.  Fluctuations in their numbers can indicate underlying health conditions.

What Factors Affect Eosinophil Count?

Several factors can influence eosinophil count including allergic reactions, parasitic infections, autoimmune disorders, medications, and environmental exposures.  

Allergies, asthma, and parasitic infections commonly lead to elevated eosinophil counts, as the body responds to these triggers by releasing eosinophils to combat the perceived threat.  

In some individuals, certain cancers or genetic alterations may cause high eosinophil counts.  

Eosinophils are produced in response to elevations in IL-5, so many pharmaceutical agents target IL-5 production to reduce eosinophil levels.  

Conversely, factors such as extreme stress, corticosteroid use, acute infections, certain endocrine disorders and certain medications may decrease eosinophil counts.  [14.]

Testing Procedure for Eosinophil Count

Eosinophil count is run as part of a complete blood count or CBC, which is considered routine blood work.

Sample Collection

Collecting a blood sample for eosinophil count typically involves venipuncture, where a healthcare professional draws blood from a vein, usually in the arm.  The collected blood sample is then transferred into a specialized tube containing an anticoagulant to prevent clotting.

Test Requirements and Preparation

Preparing for an eosinophil count test typically does not require any special preparations. However, it's essential to inform the healthcare provider about any medications or supplements being taken, as certain drugs may affect eosinophil levels. 

Additionally, it's crucial to follow any specific instructions provided by the healthcare provider regarding fasting or medication restrictions before the test. It's also essential to ensure that the blood sample is collected correctly to obtain accurate results.

Interpretation of Eosinophil Count

Reference Range for Eosinophil Count

The normal range for eosinophil count may vary among labs, but the typical reference range is 

Eosinophil blood count (absolute): 50-500/mm^3  [8.]

A count within the normal range generally suggests that the immune system is functioning adequately, while elevated or decreased counts may indicate underlying health issues that require further investigation.

Clinical Applications of Eosinophil Count

High Eosinophil Count  [2.] 

High eosinophil count is also known as eosinophilia, and is further characterized as primary or secondary.  

Primary Eosinophilia

Primary eosinophilia refers to a condition where an increased level of eosinophils in the blood or tissues occurs without an identifiable underlying cause. This type of eosinophilia is characterized by eosinophilic proliferation as a primary disorder, often involving abnormal regulation of eosinophil production or survival. 

These conditions result from intrinsic abnormalities in the bone marrow or immune system, leading to sustained elevation of eosinophil counts.

‍Secondary Eosinophilia

Secondary eosinophilia refers to an elevated level of eosinophils in the blood or tissues resulting from an underlying cause or condition rather than a primary disorder of eosinophil production or regulation. 

Secondary eosinophilia is a reactive response to external factors or underlying diseases, leading to an increase in eosinophil counts beyond normal levels. 

Degree of Eosinophilia

Eosinophilia is further characterized according to the number of eosinophils present:

• Mild eosinophilia refers to levels between 500 to 1500/mm^3
• Moderate eosinophilia refers to levels between 1500 to 5000/mm^3
• Severe eosinophilia is any number of eosinophils above 5000/mm^3

The hypereosinophilic syndrome is characterized by an absolute eosinophil count exceeding 1500/mm^3 observed on at least two occasions spaced one month apart or significant tissue eosinophilia.

Causes and Symptoms of Eosinophilia  [2.]

Primary Causes of Eosinophilia

• Chronic eosinophilic leukemia
• Myeloid and lymphoid neoplasms with rearrangements of PDGFRA, PDGFRAB, or FGFR1 genes
• Hereditary eosinophilia
• Idiopathic hypereosinophilic syndrome

Secondary Causes of Eosinophilia

• Parasitic infestations: ancylostomiasis, ascariasis, cysticercosis, echinococcosis (hydatid cyst), schistosomiasis, strongyloidiasis, trichinellosis, visceral larva migrans (toxocariasis)
• Fungal and bacterial infections: bronchopulmonary aspergillosis, chronic tuberculosis (occasionally), coccidioidomycosis, disseminated histoplasmosis, scarlet fever
• Allergic disorders: bronchial asthma, hay fever, Stevens-Johnson syndrome, drug, and food allergic reactions, DRESS syndrome
• Skin diseases: Atopic dermatitis, eczema, pemphigus, Mycosis fungoides, Sezary syndrome
• Graft versus host reaction
• Connective tissue disease: Chrug-Strauss syndrome, eosinophilic myalgia syndrome
• Miscellaneous: reactive pulmonary eosinophilia, tropical eosinophilia, pancreatitis, eosinophilic gastroenteritis

Common symptoms of eosinophilia vary depending on the underlying cause and the severity of the condition. 

In mild cases, individuals may be asymptomatic or experience nonspecific symptoms such as fatigue, weakness, or malaise.  However, in more severe cases, eosinophilia may manifest with symptoms related to organ system involvement. 

Respiratory symptoms such as coughing, wheezing, shortness of breath, or asthma exacerbations may occur if eosinophils infiltrate the lungs. 

Gastrointestinal symptoms such as abdominal pain, diarrhea, nausea, or vomiting may occur if eosinophils accumulate in the gastrointestinal tract. 

Skin manifestations such as rash, hives, or pruritus may also be present, particularly in allergic or hypersensitivity reactions. 

Systemic symptoms such as fever, weight loss, or night sweats may occur in cases of underlying systemic diseases associated with eosinophilia.

Low Eosinophil Count

Low eosinophil count is also known as eosinopenia. 

Eosinopenia is primarily observed as a secondary phenomenon, with primary or constitutional eosinopenia being extremely rare and reported only in a few cases, some of which also involve a decrease in basophils. 

When evaluating a patient with eosinopenia, a thorough investigation of potential secondary causes including medications and underlying medical conditions is essential before considering constitutional factors. 

In cases where no external cause of eosinopenia is identified, a bone marrow aspirate and biopsy may be necessary, along with comprehensive genetic testing to identify variants associated with eosinophil maturation, proliferation, and activation.  [11.] 

Causes and Symptoms of Eosinopenia

Eosinopenia is overwhelmingly a secondary manifestation of a primary condition or medication use.  

• Secondary to stress response, such as surgery, trauma, or acute illness
• Use of corticosteroids or other immunosuppressive medications
• Acute bacterial infections, especially those eliciting a strong neutrophilic response
• Overwhelming sepsis or severe bacterial infections
• Cushing syndrome or other conditions causing excess cortisol production
• Adrenal insufficiency
• Chronic inflammatory diseases, such as chronic urticaria [5.] 
• Chronic use of certain medications, including glucocorticoids, epinephrine, and theophylline  
• Specific viral infections, such as Covid-19  [12.]

Common symptoms associated with eosinopenia can vary widely depending on the underlying cause. 

In many cases, eosinopenia is a secondary phenomenon observed during acute stress responses, such as surgery, trauma, or severe bacterial infections. Therefore, symptoms may primarily reflect the underlying condition rather than eosinopenia itself. 

However, if eosinopenia persists or is associated with chronic inflammatory diseases or immunodeficiency disorders, symptoms may include recurrent infections, fatigue, weakness, and generalized malaise. 

Additionally, eosinopenia secondary to medication use or allergic reactions may present with symptoms related to the medication's side effects or the allergic response, such as skin rash, respiratory distress, or gastrointestinal disturbances. 

Eosinopenia does not always cause symptoms or hold clinical relevance, as the immune system can compensate for a lack of eosinophils.  

Management of Abnormal Eosinophil Count

Strategies to Reduce High Eosinophil Count

Identify and treat underlying causes: addressing the underlying condition or trigger of eosinophilia, such as allergies, infections, or autoimmune disorders, is essential for reducing eosinophil levels.

Avoid allergens: minimizing exposure to known airborne or digestive allergens or triggers can help prevent eosinophil activation and accumulation.

Dietary modifications: in cases of eosinophilic gastrointestinal disorders, dietary changes such as eliminating certain foods or allergens may help reduce eosinophilic inflammation.

Lifestyle modifications: employ stress management strategies to help regulate the immune system and reduce eosinophil activation.  [13.]

Treatment Options for High Eosinophil Count

Corticosteroids: oral or inhaled corticosteroids may be prescribed to suppress the immune system and reduce inflammation associated with eosinophilia.

Immunomodulators: drugs such as methotrexate or cyclosporine may be used to modulate the immune response and reduce eosinophil production.  [7.]

Biologic therapies: monoclonal antibodies such as mepolizumab or benralizumab may be prescribed to target specific proteins involved in eosinophil production and function.  [9.]

Anti-parasitic medications: in cases of eosinophilia due to parasitic infections, medications such as albendazole or ivermectin may be used to eliminate the parasites.  [10.]

Treatment Options for Low Eosinophil Count

Treatment of underlying conditions:  addressing the underlying cause of eosinopenia such as infections, inflammatory conditions, or medications, is crucial for restoring normal eosinophil levels.

Medication adjustments: if medications are responsible for causing eosinopenia, adjusting or discontinuing the offending drugs may help normalize eosinophil counts.

Immune-modulating therapies: in cases of primary eosinopenia or severe immune suppression, immune-modulating therapies such as granulocyte colony-stimulating factor (G-CSF) may be used to stimulate eosinophil production and function.  [1., 3.]

Testing Options for Eosinophil Count

Click here to review testing options and order a CBC to assess eosinophil count.