Eosinophilia (High Eosinophil Count)

What eosinophils do

Eosinophils make up about 1 to 6% of white blood cells. They are produced in the bone marrow and spend most of their time in tissues such as the gut, lungs and skin. They:

• help defend against parasitic worms
• release chemicals during allergic inflammation
• play a role in tissue repair and immune regulation

When they are overproduced or activated in large numbers, the substances they release can damage tissues.

How eosinophilia is measured

The absolute eosinophil count on a complete blood count (CBC) is used, rather than the percentage.

Hypereosinophilia means a count above 1,500 on two tests at least a month apart, or tissue damage caused by eosinophils.

Eosinophils can also build up in particular tissues without high blood levels, as in eosinophilic esophagitis.

Causes of eosinophilia

A common memory aid is "allergies, parasites, drugs and other".

Allergic conditions (most common in the US and Europe)

• Asthma and allergic rhinitis
• Eczema (atopic dermatitis)
• Food allergies and eosinophilic esophagitis
• Allergic bronchopulmonary aspergillosis

Allergies usually cause mild eosinophilia. Higher counts suggest another cause.

Parasitic infections (most common worldwide)

Parasitic infections involving tissue-invading worms, such as:

• Strongyloides, which can persist for decades and become life-threatening if steroids are given
• hookworm, roundworm (Ascaris), Toxocara (from dogs and cats)
• schistosomiasis, filariasis and liver flukes
• trichinosis from undercooked meat

Pinworms and intestinal protozoa such as Giardia rarely cause eosinophilia.

Medicines

Many medicines can cause eosinophilia, from a harmless rise to a severe reaction. Common culprits include antibiotics (penicillins, sulfonamides), anticonvulsants (carbamazepine, phenytoin, lamotrigine), allopurinol and NSAIDs. DRESS syndrome is a serious reaction with fever, rash and organ inflammation.

Autoimmune and inflammatory conditions

• Eosinophilic granulomatosis with polyangiitis (Churg-Strauss syndrome): asthma, sinusitis and vasculitis
• Inflammatory bowel disease
• Sarcoidosis
• Eosinophilic fasciitis

Hormonal

• Adrenal insufficiency (Addison's disease), because cortisol normally keeps eosinophil counts down

Cancers and blood disorders

• Hodgkin lymphoma and some T-cell lymphomas
• Myeloid neoplasms and chronic eosinophilic leukemia, sometimes with specific gene changes (such as PDGFRA)
• Solid tumors, occasionally

Hypereosinophilic syndrome

Hypereosinophilic syndrome is diagnosed when a persistent count over 1,500 causes organ damage and no other cause is found.

Symptoms

Eosinophilia itself often causes no symptoms. Symptoms usually come from the underlying cause or from organ damage:

• Skin: itching, rash, hives, swelling
• Lungs: cough, wheeze, breathlessness
• Gut: abdominal pain, diarrhea, difficulty swallowing
• Heart: chest pain, breathlessness, heart failure (with high counts)
• Nerves: numbness, tingling, weakness
• General: fever, weight loss, night sweats, tiredness

Diagnosis

1. Repeat complete blood count to confirm and track the count.
2. History: allergies, asthma, medicines started in the last 2 to 3 months, travel, migration, diet (raw meat or fish), pets, and symptoms.
3. Parasite tests: stool samples for ova and parasites, and Strongyloides blood antibody tests, especially with relevant travel or residence.
4. Blood tests: liver and kidney function, IgE, cortisol, inflammatory markers, ANCA for vasculitis, and troponin if the heart may be involved.
5. Chest X-ray, echocardiogram and other imaging depending on symptoms.
6. Bone marrow biopsy and genetic tests if a blood disorder is suspected.

Treatment

Treatment targets the cause:

• Allergies and asthma: allergen avoidance, inhaled steroids, antihistamines, and biologic medicines that lower eosinophils (such as mepolizumab or benralizumab) for severe eosinophilic asthma
• Parasites: antiparasitic medicines such as ivermectin or albendazole
• Medicines: stopping the responsible drug. DRESS may need steroids and hospital care
• Autoimmune conditions: steroids and immune-suppressing medicines
• Adrenal insufficiency: hormone replacement
• Blood disorders: targeted therapies such as imatinib for PDGFRA-positive disease
• Hypereosinophilic syndrome: steroids, other medicines and biologics

Frequently asked questions

What does a high eosinophil count mean?

It means your blood has more eosinophils than normal, usually above 500 per microliter. The most common reasons are allergies, asthma, eczema, parasitic infections and medicines. Less often it reflects autoimmune disease, adrenal insufficiency or a blood disorder.

Is eosinophilia serious?

Mild eosinophilia is usually not serious and often reflects allergies. Counts above 1,500 that persist can damage organs such as the heart, lungs and nerves, and need prompt evaluation. The seriousness depends on the cause.

What is the most common cause of eosinophilia?

In the US and other developed countries, allergic conditions such as asthma, hay fever and eczema are the most common causes. Worldwide, parasitic worm infections are the most common cause.

Can stress cause high eosinophils?

No. Stress actually tends to lower eosinophil counts, because stress hormones such as cortisol suppress them. A high count should prompt a search for causes such as allergies, parasites or medicines.

How do you lower eosinophils?

Lowering eosinophils means treating the cause: managing allergies and asthma, treating parasites, stopping a triggering medicine, or treating an autoimmune or blood disorder. Steroids and biologic medicines lower eosinophils when needed.