Diagnosis

A diagnosis of is HES is based on persistent high levels of eosinophils and evidence of organ damage. Diagnostic tests are used to determine what has caused an increase of eosinophils and whether any tissues have been affected.

Your healthcare professional will ask a number of questions about symptoms, family medical history, medicines and possible exposure to disease.

Tests to determine cause

Your healthcare professional orders tests to determine the cause of increased eosinophils. These may include:

  • Blood tests to detect autoimmune conditions, infections, or evidence of blood-related cancers.
  • Allergy tests to detect environmental or food allergies.
  • Stool tests to detect parasitic infections such as hookworm.
  • Genetic test to check for rare gene mutations that can cause HES.
  • Bone marrow samples to detect possible cancers or other diseases of the bone marrow.

Tests to assess organ damage

Other tests are used to find out whether organs have been affected by high eosinophils. These may include:

  • Blood tests to check liver and kidney function.
  • Imaging tests to study the appearance and function of organs.
  • Echocardiogram to check heart function.
  • Lung function tests to measure how well you breathe in and out.
  • Tissue samples of organs that check for the presence of eosinophils or evidence of tissue damage.

Treatment

Treatment goals are to reduce eosinophil levels, lessen symptoms and prevent further damage to organs.

If an underlying cause is found, treatment for that condition also begins.

Medicines

The first line of treatment is usually a corticosteroid to lower the number of eosinophils circulating in the bloodstream.

Other medicines may be used depending on the cause of increased eosinophils or the response to corticosteroid treatment. They include:

  • Hydroxyurea (Droxia, Hydrea, others).
  • Imatinib (Gleevec).
  • Mepolizumab (Nucala).
  • Vincristine PFS.

Because HES can increase your risk of blood clots, you also may be prescribed blood-thinning medications such as warfarin (Coumadin).

Clinical trials

Explore Mayo Clinic studies testing new treatments, interventions and tests as a means to prevent, detect, treat or manage this condition.

Preparing for your appointment

You'll likely begin with an appointment with your primary healthcare professional. Depending on the results of early tests and symptoms, you may need an appointment with specialists in multiple fields. The healthcare team may include a specialist in the following fields:

  • Allergies, called an allergist.
  • Blood disorders, called a hematologist.

Consider taking a relative or friend along to your appointments to help remember all the information provided.

Here's some information to help you get ready for an appointment, and what to expect from your healthcare professionals.

What you can do

Before your appointment, make a list of:

  • Signs and symptoms, including any that seem unrelated to the reason for the appointment.
  • Any medications, including vitamins, herbs and over-the-counter medicines; the dosages for each; and reasons for taking them.
  • Key personal information, including any major stresses or recent changes in your life.

If HES is considered or you have a diagnosis of HES, you might ask these questions:

  • Will I need additional tests?
  • What are the treatment options?
  • What are the benefits and risks of each treatment?
  • Should I see additional specialists?
  • What tests or appointments are the highest priority?
  • Are there brochures or other printed material that I can have? What websites do you recommend?

What to expect from your doctor

The healthcare professional is likely to ask you several questions. Be ready to answer them to allow time later to cover other points you want to address. Examples include:

  • When did you first begin experiencing symptoms?
  • Are the symptoms continuous or occasional?
  • How severe are the symptoms?
  • What, if anything, seems to improve your symptoms?
  • What, if anything, appears to worsen the symptoms?
  • Do you have any allergies or skin conditions?
  • Have you been exposed to any parasites such as hookworm?
  • Have you traveled out of the country lately?
  • Have you recently started a new medicine?
  • Does anyone in your family have a history of HES?
June 27, 2025

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  1. Roufosse F, et al. Hypereosinophilic syndromes: Clinical manifestations, pathophysiology, and diagnosis. https://www.uptodate.com/contents/search. Accessed Nov. 18, 2024.
  2. Ferri FF. Hypereosinophilic syndrome. In: Ferri's Clinical Advisor 2025. Elsevier; 2025. https://www.clinicalkey.com. Accessed Nov. 18, 2024.
  3. Hoffman R, et al. Eosinophilia, eosinophilic neoplasms, and the hypereosinophilic syndromes. In: Hematology: Basic Principles and Practice. 8th ed. Elsevier; 2023. https://www.clinicalkey.com. Accessed Nov. 18, 2024.
  4. Eosinophil production and function. Merck Manual Professional Version. https://www.merckmanuals.com/professional/hematology-and-oncology/eosinophilic-disorders/eosinophil-production-and-function. Accessed Nov. 22, 2024.
  5. Marra AM, et al. Eosinophil-associated diseases: The allergist's and clinical immunologist's perspective. European Annals of Allergy and Clinical Immunology. 2024; doi:10.23822/EurAnnACI.1764-1489.339.
  6. Rosenberg CE, et al. Diagnosis and management of pediatric hypereosinophilic syndrome. Journal of Allergy and Clinical Immunology: In Practice. 2022; doi:10.1016/j.jaip.2022.02.007.
  7. Roufosse F, et al. Hypereosinophilic syndromes: Treatment. https://www.uptodate.com/contents/search. Accessed Nov. 18, 2024.
  8. Klion AD. Approach to the patient with suspected hypereosinophilic syndrome. Hematology, American Society of Hematology Education Program. 2022; doi:10.1182/hematology.2022000367.

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