What Does High Eosinophils Mean? A Comprehensive Guide for Patients and Practitioners

Eosinophils are a type of white blood cell, along with monocytes, neutrophils, and basophils, that play a vital role in the immune system.

They are particularly involved in the body’s defenses against allergens, fungal infections, and parasitic infections. Several conditions can cause a high number of eosinophils in the blood, a condition known as eosinophilia. Eosinophilia is also associated with inflammatory responses.

A normal eosinophil count is usually part of a complete blood count (CBC). A normal count is less than 500 cells per microliter (cells/mcL). When comparing results, it’s essential to confirm that measurements use the same units, as test results may vary in format, such as cells per microliter (mcL) or cubic millimeter (mm³).

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What Causes High Eosinophils?

A variety of conditions can cause eosinophilia. While a few can be serious, most causes are nothing to be alarmed about. Patients are encouraged to discuss test results with their healthcare provider to understand the significance of an abnormal eosinophil count.

In addition, high eosinophils can be a sign of inflammation, and inflammatory responses can cause high cortisol levels and other systemic issues.

For example, high eosinophils can be caused by something as simple as hay fever and other seasonal allergies. Eosinophilia may also be associated with asthma, particularly in environments with additional breathing challenges, such as areas with high dust levels.

Even a simple infection can cause high eosinophils. While they only make up 1% of the cells in a body, they are prominent in the immune system’s response to attack.

Aside from those basic reasons, why would eosinophils be high?

Immune regulation problems
Autoimmune diseases
Inflammatory bowel disease
Myocarditis
Vasculitis
Sarcoidosis
Genetic eosinophilia
Some cancers

Finally, there are some eosinophil-related disorders where high eosinophils will have direct inflammatory effects on specific body parts. These eosinophilic disorders, or hypereosinophilia syndromes (HES), are named for the affected body parts. Eosinophilic disorders are usually marked by 1,500 cells/mcL or more. These disorders include:

Eosinophilic cystitis is a bladder disorder.
Eosinophilic fasciitis affects connective tissue throughout the body.
Eosinophilic pneumonia affects the lungs.
Eosinophilic gastrointestinal disorders (EGID) affect the esophagus, colon, stomach, and small intestine.
Eosinophilic granulomatosis with polyangiitis (EGPA), also known as Churg-Strauss syndrome, affects the lungs, heart, sinuses, and sometimes other organs.

Hypereosinophilic Syndrome

Since eosinophilia is common, it can be difficult to determine what is an alarming number of eosinophils. The range of eosinophils in the blood and their duration are determining factors for further investigation.

When eosinophil levels reach 1,500 cells per microliter of blood (or 1.5 × 10^9 per liter) for six months or longer, healthcare providers may consider evaluating for hypereosinophilic syndrome, a more serious condition.

Hypereosinophilic syndrome (HES) is a rare group of conditions that affects the heart, central nervous system, skin, and respiratory tract and can be caused by a chromosomal disorder or other contributing factors.

While hypereosinophilic syndrome can occur at any age, it is most common in men older than 50.

This increase in inflammation may contribute to conditions affecting the heart, including cardiac inflammation (known as Löffler endocarditis), as well as risks of blood clots, heart failure, or other cardiovascular concerns.

Symptoms of hypereosinophilic syndrome include:

weight loss
fevers
night sweats
fatigue
cough
chest pain
swelling
stomachache
rash
pain
weakness
confusion
coma

Hypereosinophilic syndrome is a serious condition; without treatment, it may significantly impact survival, with healthcare data suggesting decreased survival rates within two years. However, with treatment more than 80% survive. Heart damage is the principal cause of death.

Eosinophils and Cancer

When eosinophils exceed 5,000 cells per microliter of blood, this level may require further investigation and close medical evaluation. This can happen in cases of sepsis or cancer, including Hodkin’s lymphoma, breast, colorectal, cervical, ovarian, and prostate cancers.

In such a situation, another test known as an absolute eosinophil test should be done. This is a more detailed blood test that only looks at the eosinophils and is more accurate than a basic CBC eosinophil test.

Treatment for High Eosinophils

The treatment for high eosinophil levels will depend upon the cause. To address high eosinophils, a physician will typically work to identify and treat the underlying cause, which may help reduce eosinophil levels.

For example, if the patient has a bacterial infection, a simple course of antibiotics will kill the infection and lower the eosinophilic response.

In patients with primary eosinophilia without organ involvement, usually, no treatment is necessary. However, cardiac function should be evaluated at regular intervals.

Treatment of primary eosinophilia with organ involvement often begins with corticosteroids, and, if necessary, interferon (IFN)-alpha for steroid-resistant disease. Long-term maintenance for organ involvement includes:

For severe cases with cancers, imatinib has achieved complete and durable remissions and has become established as the definitive first-line therapy. Unfortunately, there is a high reoccurrence rate once the treatment is ceased.

However, hypereosinophilic syndrome has shown a limited response rate to imatinib in some cases. Treatment with antibodies and antibody-based agents (eg, mepolizumab, alemtuzumab, brentuximab vedotin) has shown to be effective in some patients with HES.

A 2013 study highlighted that recent drug development efforts are increasingly aimed at preventing eosinophils from accumulating in organs and reducing their survival and activity. Early clinical trials are underway with the first generation of therapies specifically targeting eosinophils, particularly focusing on IL-5 and its receptor, showing potential for managing conditions linked to elevated eosinophil levels.

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Key Takeaways

Eosinophils are an essential part of the body’s immune system, and elevated levels in the blood may indicate underlying health conditions. These can range from very mild diseases, such as allergic hay fever, to very serious conditions, including Hypereosinophilic Syndrome and several cancers.
When eosinophil levels are elevated, consulting a healthcare provider is recommended to understand the underlying cause and whether additional evaluation is needed.
Depending on the underlying cause and severity, eosinophilia management may involve options ranging from lifestyle adjustments to medical treatments.