The absolute eosinophil count measures the number of eosinophils in the blood. Eosinophils are a type of white blood cell that plays a critical role in the body’s immune response, particularly in fighting parasitic infections and mediating allergic reactions. They also participate in inflammatory processes and contribute to tissue damage in certain diseases.

Normal Range:

• The normal absolute eosinophil count typically ranges from 50 to 500 cells/μL (1–4% of the total white blood cells). However, this range can vary slightly depending on the laboratory standards.

Uses of the Absolute Eosinophil Count:

• Diagnosis and Monitoring of Allergic Disorders:
• Conditions like asthma, allergic rhinitis, and atopic dermatitis often cause elevated eosinophil levels.
• Detection of Parasitic Infections:
• Eosinophilia is common in patients with helminthic (worm) infections.
• Evaluation of Autoimmune Diseases:
• Certain autoimmune conditions, such as eosinophilic granulomatosis with polyangiitis (EGPA), involve high eosinophil counts.
• Assessment of Hematologic Conditions:
• Persistent eosinophilia may be seen in blood cancers such as Hodgkin lymphoma or certain leukemias.

Interpretation of Results:

• High Absolute Eosinophil Count (Eosinophilia):
• Allergic conditions: Such as asthma, hay fever, and drug hypersensitivity reactions.
• Parasitic infections: Eosinophilia is a hallmark of many helminthic infections, such as those caused by roundworms or flukes.
• Autoimmune diseases: Eosinophilic granulomatosis with polyangiitis and certain types of vasculitis may show high eosinophil counts.
• Cancers: Some blood cancers, like Hodgkin lymphoma or certain myeloproliferative disorders, can present with elevated eosinophil counts.
• Hypereosinophilic syndrome (HES): A rare disorder characterized by persistently high eosinophil counts that can lead to organ damage.
• Low Absolute Eosinophil Count:
• Typically not concerning: Low eosinophil counts are generally not clinically significant on their own.
• Stress or acute infections: The body’s response to stress or acute bacterial or viral infections may suppress eosinophil levels.
• Corticosteroid use: Medications such as corticosteroids can decrease eosinophil levels as they suppress inflammation.

Clinical Considerations:

• Persistent Eosinophilia: When eosinophilia is sustained or significantly elevated, further investigation is needed to identify an underlying cause, which may include blood tests for allergies, stool tests for parasites, imaging, or bone marrow biopsy.
• Episodic Eosinophilia: This can be related to conditions like asthma flare-ups or seasonal allergies.

Associated Tests:

• Complete Blood Count (CBC) with Differential: Used to measure the percentages and absolute counts of all types of white blood cells.
• Allergy Testing: For patients with suspected allergic reactions.
• Parasitic Infection Workup: Stool tests and serologic tests to identify parasitic causes.
• Imaging and Biopsy: May be performed in cases where tissue infiltration by eosinophils is suspected.

Limitations:

• Transient Changes: Eosinophil levels can be affected by transient factors such as recent infections, medication use, and stress.
• Not Specific Alone: The absolute eosinophil count must be interpreted within the context of the patient's overall clinical picture, including symptoms and other test results.

Conclusion:

The absolute eosinophil count is a useful tool for diagnosing and monitoring a range of conditions related to allergies, infections, and hematologic disorders. It provides valuable insights but must be combined with a detailed patient history and other diagnostic evaluations for accurate clinical interpretation.