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    Definition of eosinophilia

    Eosinophilia (e-o-sin-o-FIL-e-uh) is a higher than normal level of eosinophils. Eosinophils are a type of disease-fighting white blood cell.

    You can have high levels of eosinophils in your blood (blood eosinophilia). High levels of eosinophils may also occur in your body’s tissues at the site of an infection or inflammation (tissue eosinophilia).

    Tissue eosinophilia may be found in samples taken during an exploratory procedure or in samples of certain fluids, such as mucus released from nasal tissues. If you have tissue eosinophilia, the level of eosinophils in your bloodstream is likely normal.

    Blood eosinophilia may be detected with a blood test, usually as part of a complete blood count. A count of more than 500 eosinophils per microliter of blood is generally considered eosinophilia in adults. A count of more than 1,500 eosinophils per microliter of blood that lasts for several months is called hypereosinophilic syndrome.

    Causes of eosinophilia

    Eosinophils play two roles in your immune system:

    • Destroying foreign substances. Eosinophils can consume foreign substances — particularly substances related to infection with a parasite — that have been “flagged” for destruction by other components of your immune system.
    • Regulating inflammation. Eosinophils help promote inflammation, which plays a beneficial role in isolating and controlling a disease site. But, sometimes inflammation may be greater than is necessary, which can lead to troublesome symptoms or even tissue damage. For example, eosinophils play a key role in the symptoms of asthma and allergies, such as hay fever. Other immune system disorders also can contribute to ongoing (chronic) inflammation.

    Eosinophilia occurs when either a large number of eosinophils are recruited to a specific site in your body or bone marrow produces too many eosinophils. This can be caused by a variety of conditions, diseases and factors, including:

    1. Parasitic and fungal diseases
    2. Allergies, including to medications or food
    3. Adrenal conditions
    4. Skin disorders
    5. Toxins
    6. Autoimmune diseases
    7. Endocrine disorders
    8. Tumors

    Specific diseases and conditions that can result in blood or tissue eosinophilia include:

    1. Ascariasis (a roundworm infection)
    2. Asthma
    3. Atopic dermatitis (eczema)
    4. Chronic myelogenous leukemia
    5. Churg-Strauss syndrome
    6. Crohn’s disease
    7. Drug allergy
    8. Eosinophilic leukemia
    9. Hay fever
    10. Hodgkin’s lymphoma (Hodgkin’s disease)
    11. Idiopathic hypereosinophilic syndrome (HES), an extremely high eosinophil count of unknown origin
    12. Lupus
    13. Lymphatic filariasis (a parasitic infection)
    14. Other cancers
    15. Other parasitic infections
    16. Ovarian cancer
    17. Primary immunodeficiency
    18. Trichinosis (a roundworm infection)
    19. Ulcerative colitis

    Parasitic diseases and allergic reactions to medication are among the more common causes of eosinophilia. Hypereosinophilic syndrome tends to have an unknown cause or results from certain types of cancer, such as bone marrow or lymph node cancer.

    When to see a doctor

    Eosinophilia is usually found when your doctor has ordered blood tests to help diagnose a condition you’re already experiencing. It’s usually not an unexpected finding, but it’s possible that it may be discovered simply by chance.

    Talk to your doctor about what these results mean. Evidence of blood or tissue eosinophilia and results from other tests may indicate the cause of your illness, or your doctor may suggest other tests to check your condition.

    Because a separate condition is often the cause of eosinophilia, it’s important to determine what other conditions or disorders you may have. If you get an accurate diagnosis and can receive treatment for any relevant conditions or disorders, the eosinophilia will likely resolve.

    However, if you have hypereosinophilic syndrome, your doctor may prescribe medications, such as corticosteroids, and he or she will want to monitor your health, as this condition may cause significant complications over time.