What is Eosinophilia?

Illustration of red blood cells and white blood cells
Illustration of red blood cells and white blood cells. Callista Images/Creative RF/Getty Images


Eosinophilia is the technical name for an elevated eosinophil count.  Eosinophils are a type of white blood cells that destroy substances in the body like parasites and participate in inflammatory reactions.  

What are the categories of eosinophilia?

Eosinophilia can be categorized by the number of eosinophils (absolute eosinophil count).  

  • Mild:  500 - 1500 cells/mL
  • Moderate:  1500 - 5000 cells/mL
  • Severe:  > 5000 cells/mL

How is eosinophilia diagnosed?

Like most blood disorders, eosinophilia is identified on complete blood count (CBC).  Eosinophils are one of the white blood cells and are found in the portion of the CBC called the differential. The differential reports how many of each type of white blood cells (neutrophil, lymphocyte, monocyte, eosinophil, and basophil) are present.  It is important that eosinophilia be diagnosed by using the absolute eosinophil count, rather than the percent of eosinophils that are present.  

After identification of eosinophilia, your healthcare provider will start working towards identifying the cause.  The severity of eosinophilia sometimes can direct the work-up needed.  

What are the causes of eosinophilia?  

  1. Parasite infections:  Worldwide the most common cause of eosinophilia is parasite infections.  These include schistosomiasis, trichinosis, strongyloidiasis, and ascariasis.  In generally these are different parasites than those that cause “travelers’ diarrhea”.  Travel history is an important part of the work-up for eosinophilia although a lack of recent travel does not rule out parasitic infections.  Testing usually involves stool studies and blood work looking for the source of the infection.  
  1. Drug reactions:  Medications can trigger eosinophilia, sometimes without clinical symptoms.  The most common medications associated with eosinophilia include antibiotics (penicillin, cephalosporins), non-steroidal anti-inflammatory medications (aspirin, ibuprofen), ranitidine (for gastroesophageal reflux), phenytoin (anti-seizure) and allopurinol (used to treat gout).  The most severe form is called drug reaction with eosinophilia and systemic symptoms (DRESS).  This is a rare, potentially life threatening, hypersensitivity reaction.  There can be a prolonged period time between drug exposure and symptoms in DRESS.  
  1. Asthma, seasonal allergies, and eczema:  These three are sometimes called the atopic triad.  These can be some of the most common causes of mild to moderate eosinophilia, particularly in children.  Food allergies can also cause elevated eosinophil counts.   
  2. Eosinophilia esophagitis (EoE):  This is a disorder characterized by eosinophil invasion of the esophageal tissues which normally contain  no eosinophils.  About 50% of patients will also have blood eosinophilia.  Eosinophilia esophagitis may cause difficulty swallowing, chest/abdominal pain, vomiting or food impaction.  Diagnosis requires biopsy of the esophagus.  
  3. Hypereosinophilic syndromes:  Hyperoeosinophilic syndromes (HES) are a group of disorders characterized by eosinophil counts  > 1500 cells/mL and evidence of organ damage from the abundance of eosinophils.  Organs commonly targeted are skin, lung, and gastrointestinal tract. HES can be primary (also called neoplastic) secondary (reactive) or idiopathic (cause unknown).   
  1. Churg-Strauss Syndrome:  Churg-Stauss vasculitis, now called eosinophilic granulomatosis with polyangiitis.  Patients present with asthma and other lung issues initially, then eosinophilia, and then go on to develop vasculitis.  
  2. Cancers:  There are several cancers, particularly blood cancers, that are known for increasing the eosinophil count.  These include a rare type of acute myeloid leukemia called eosinophilic leukemia.  Several of the myeloproliferative disorders (essential thrombocythemia, polycythemia vera) can present with eosinophilia.  Both B-cell and T-cell lymphoma may trigger eosinophilia.  Adenocarcinomas of the GI tract, lung, and cervix are other potentials.  

 What are the treatments for eosinophilia?

Treatment is determined by the cause of eosinophilia.  If the eosinophilia is mild, observation with repeat labs may be recommended.    

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