Eosinophilia

Eosinophilia means there are more eosinophils in the blood than normal. Eosinophils are white blood cells involved in allergic reactions and in fighting parasites. Common causes include allergies, asthma, eczema and drug reactions. Parasitic infections are an important cause, especially after travel or in people from areas where parasites are common. Less common causes include some autoimmune and inflammatory diseases, adrenal insufficiency, and some blood disorders and cancers.

Lab tests linked to eosinophilia:

• Eosinophils (percent): the share of white cells that are eosinophils.
• Doctors look mainly at the absolute eosinophil count on a CBC. They may also order stool tests for parasites, Strongyloides antibodies, total IgE, vitamin B12, tryptase, and tests of organs that eosinophils can affect, such as the heart and lungs.

How results are read:

• The absolute count matters more than the percentage. A raised percentage can reflect a low count of other white cells.
• Mild eosinophilia is common with allergies and often needs no specific workup.
• Higher counts that persist, often called hypereosinophilia, need investigation because eosinophils can damage organs over time.
• Before planned steroid treatment, doctors assess Strongyloides risk from where a person has lived or traveled, and arrange screening or treatment when needed.

When to see a doctor:

• See a doctor about a persistently raised eosinophil count, especially with weight loss, cough, rash or diarrhea.
• Get emergency care for a spreading rash with fever after starting a new medicine, or new chest pain or breathlessness.

Clinical takeaway: eosinophilia is judged by the absolute count, and persistent or high levels are investigated for allergies, parasites, medicines and less common blood or immune causes.