What is eosinophilia?

Eosinophilia refers to a condition of having an increased numbers of eosinophils in the peripheral blood. White blood cells are an essential component of the cellular immune system. Eosinophils are specific white blood cells that are a normal part of the cellular immune system, play a role in normal physiologic processes and host defense, and participate in allergic reactions and the defense against parasitic infections.

Eosinophilia is said to occur when there are greater than 500 eosinophils per microliter, though the exact cutoff varies by laboratory. Eosinophilia can be considered mild, moderate or severe. Usually, less than 5% of the circulating white blood cells in a person are eosinophils.

Symptoms and Causes

What causes eosinophilia?

Causes range from less serious but very common conditions such as nasal allergy and asthma to more serious hematologic conditions, including:

  • Allergies and asthma
  • Drug allergy
  • Infections (mostly from parasites)
  • Blood disorders and cancers
  • Autoimmune disease
  • Endocrine disorders
  • Diseases involving organs and systems, including the:
    • Skin
    • Lungs
    • Gastrointestinal system
    • Neurological system
    • Joints, muscles and connective tissue
    • Heart

Eosinophilic disorders are often called by names that reflect where the problem is located. These include:

  • Eosinophilic cystitis, a disorder of the bladder
  • Eosinophilic fasciitis, a disorder of the fascia, or the connective tissue throughout the body
  • Eosinophilic pneumonia, a disorder of the lungs
  • Eosinophilic colitis, a disorder of the colon (large intestine)
  • Eosinophilic esophagitis, a disorder of the esophagus
  • Eosinophilic gastritis, a disorder of the stomach
  • Eosinophilic gastroenteritis, a disorder of both the stomach and the small intestine

The last four types on the list are known as eosinophilic gastrointestinal disorders (EGIDs). This category of disease is increasing. Eosinophilic granulomatosis with polyangiitis involves the lungs, heart, sinuses, and other organs. It is also known as Churg-Strauss syndrome. Another condition is hypereosinophilic syndrome, which is a primary hematologic disorder involving the blood and other organs.

Diagnosis and Tests

How is eosinophilia diagnosed?

Elevated peripheral blood eosinophils can be found during blood testing. Depending on what the cause could be, your doctor might order more tests. Other tests might include:

  • Liver function tests
  • Chest X-rays
  • Urine tests
  • Further blood tests
  • Tissue and bone marrow biopsies
  • Stool sample testing

Management and Treatment

How is eosinophilia treated?

Treatment depends on the cause of the condition. Treatments might include stopping certain medications (in the case of drug reactions), avoiding certain foods (in the case of esophagitis), or taking an anti-infective or anti-inflammatory medication. Treatments that target eosinophils in asthma specifically have been approved by the Food & Drug Administration (FDA) and are being used in the clinic, while treatments for other eosinophil-mediated conditions are under further investigation.

Outlook / Prognosis

What is the outlook for eosinophilia?

Treating the cause of high eosinophil counts affects the outcome. In more serious conditions, outcomes also depend on the extent of target organ and how the person responds to treatment.

Last reviewed by a Cleveland Clinic medical professional on 02/15/2018.


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