An Overview of Eosinophilia

Eosinophilia is the medical term for an increased eosinophil count. Eosinophils are a type of white blood cell. When elevated, it may suggest an underlying health concern.

Causes of high eosinophils, as measured by blood test results, range from relatively benign food allergies to parasite infections, or far more serious types of cancer or COVID-related illness.

This article discusses the symptoms and causes of eosinophilia, as well as how some of the conditions that cause it may be diagnosed and treated.

Symptoms

If you have eosinophilia, your symptoms will partially be determined by the cause of the elevated eosinophilia count. If your eosinophil count is mildly elevated you may not have any symptoms.

Common symptoms include:

• Rash
• Itching
• Diarrhea, in the case of parasite infections
• Asthma
• Runny nose, particularly if associated with allergies
• A chronic eosinophilia cough

Causes

There are numerous reasons your eosinophil count may be elevated. Some of the causes are benign and require little treatment. It is not uncommon for the elevated count to be transient and resolve without treatment.

Parasite infections

Parasitic infections are among the most common infectious diseases globally, and often linked to eosinophilia. These infections include schistosomiasis, trichinosis, strongyloidiasis, and ascariasis.

Travel history is an important part of the work-up for eosinophilia, although a lack of recent travel does not rule out parasitic infections.

Drug reactions

Medications can trigger eosinophilia, sometimes without any obvious signs or symptoms. The most common medications associated with eosinophilia include:

• Antibiotics (penicillin, cephalosporins)
• Non-steroidal anti-inflammatory medications (aspirin, ibuprofen)
• Anti-seizure drugs (phenytoin)
• Gout medication (allopurinol)

The most severe form is called drug reaction with eosinophilia and systemic symptoms (DRESS). Fortunately, most people will not have these reactions when they receive these medications.

Atopy

Atopy is a type of reaction that occurs in the body. Typically, atopy refers to asthma, seasonal allergies (also called allergic rhinitis), and eczema. It is not uncommon for someone to have more than one of these medical conditions, as they are related.

These are some of the most common causes of mild to moderate eosinophilia, especially when eosinophils are high in a child. Similarly, food allergies can also cause elevated eosinophil counts.

Eosinophilic Esophagitis

Eosinophilic esophagitis (EoE) is a disorder characterized by eosinophils spreading to the esophagus, which normally does not contain them. About 50% of people with EoE will also have elevated eosinophil counts in the blood.

Hypereosinophilic Syndromes

Hypereosinophilic syndromes (HES) are a group of disorders characterized by very high eosinophil counts and evidence of organ damage from a large number of eosinophils. Organs commonly targeted are the skin, lung, and gastrointestinal tract. HES can be primary (also called neoplastic) secondary (reactive) or idiopathic (cause unknown).  

Churg-Strauss Syndrome

Churg-Stauss vasculitis, now called eosinophilic granulomatosis with polyangiitis, can cause eosiniophilia. People with this condition present with asthma and other lung issues initially, then develop eosinophilia, and eventually vasculitis, an inflammation of the blood vessels. 

Cancer

There are several cancers, particularly blood cancers, that are known for increasing the eosinophil count, including:

• Lymphoma (Hodgkin's and non-Hodgkin's lymphoma)
• Leukemia (chronic myeloid leukemia, adult T-cell leukemia/lymphoma, eosinophilic leukemia)
• Colorectal cancer
  
• Lung cancer

These include a rare type of acute myeloid leukemia (AML) called eosinophilic leukemia. Other causes include several of the myeloproliferative neoplasms (such as essential thrombocythemia and polycythemia vera) and cancers of the cervix.

Diagnosis

Like most blood disorders, eosinophilia is identified on complete blood count (CBC). They are one of the white blood cells found in the portion of the CBC called the differential.

After identification of eosinophilia, your healthcare provider will start working towards identifying the cause. Sometimes, this requires referral to a hematologist.

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

• Mild: 500 - 1500 cells per microliter (mcL)
• Moderate: 1500 - 5000 cells/mcL
• Severe: more than 5000 cells/mcL

The cause of your eosinophilia will be based on your symptoms. For example, EoE also may cause difficulty swallowing and diagnosis requires a biopsy of the esophagus. Many of the parasite infections are diagnosed by taking stool samples and testing them.

There may not be a test to determine if a medication is the cause of your eosinophilia. If your eosinophil count returns to normal after discontinuing the medications, it is usually presumed that the medication was the cause. 

Treatment

Treatment is determined by the cause of eosinophilia. Options include:

• Observation if your eosinophilia is mild, with repeat labs that may be recommended
• Discontinued medication, if found to be causing your elevated eosinophil count
• Therapy for asthma, eczema, and allergies
• Anti-parasitic medications for parasite infections
• Steroids such as prednisone to treat hypereosinophilic syndromes

A Word From Verywell

Eosinophilia is a scary-sounding word. Fortunately, for most people with this condition, it is transient and requires little to no treatment. For some, diagnosis and treatment may require referral to a specialist. If you have additional concerns, make sure to discuss them with your physician.