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Hematology

Eosinophils: Clues to Allergy and Immune Response

Eosinophils are white blood cells involved in allergic reactions and the defence against parasites. As part of your complete blood count, they can offer clues about allergies or asthma. A raised count is often seen with allergic complaints, while a low count is usually not a concern.

Doctor's Assessment Included

Eosinophils: what this test measures

Eosinophils are white blood cells that play an important role in allergic reactions and in defence against parasites. They contain granules with substances that are released during an allergic or inflammatory reaction.

This test measures how many eosinophils are present in your blood, as part of a complete blood count with differential. Normally eosinophils make up only a small part of your white blood cells, so even a slight rise can stand out.

The result is often given as both an absolute number and a percentage, and assessed together with your symptoms.

Eosinophils: why this value matters

The eosinophil count can help your doctor find clues to allergic and other conditions. A raised count (eosinophilia) is common with allergies such as hay fever, with asthma, with eczema and with a parasitic infection.

Because eosinophils respond to allergic triggers, the value can change with the season or with exposure to certain substances. A strongly raised count calls for further investigation to find the cause.

A low eosinophil count rarely has meaning and is usually not regarded as abnormal. The emphasis with this value is therefore mainly on a rise.

Eosinophils: when is testing worthwhile?

Eosinophils are measured within a complete blood count with differential. Your doctor may pay particular attention to them with allergy symptoms, asthma, persistent skin complaints such as itching or eczema, or a suspected parasitic infection.

The value can also be useful to monitor when a raised count was found previously, to see whether it is rising or falling.

Because the eosinophil count can fluctuate, your doctor always interprets a result together with your symptoms, your history and any follow-up testing.

Eosinophils: symptoms of a high or low value

Low Levels

A low eosinophil count almost never has consequences and usually causes no symptoms. It is rarely regarded as a problem.

High Levels

A raised eosinophil count usually causes no symptoms by itself; the symptoms relate to the underlying cause. With an allergy or asthma you may have sneezing, a runny nose, itching, breathlessness or a skin rash. With a parasitic infection there can be abdominal complaints or other symptoms that fit the cause.

Eosinophils: lifestyle and this value

If you have allergy or asthma symptoms, it can help to avoid known triggers such as pollen, house dust mites or animal allergens as much as possible. Good treatment of your allergy or asthma can help reduce symptoms and sometimes the eosinophil count too.

A persistently raised eosinophil count should always be assessed by a doctor, so that the cause becomes clear and appropriate treatment can be started.

Eosinophils: frequently asked questions

What does a high eosinophil count mean?

A raised count (eosinophilia) is often linked to allergies, asthma or a parasitic infection. Your doctor interprets it together with your history and other values.

Is a low eosinophil count a problem?

A low eosinophil count is common and is generally not a cause for concern on its own.

Are eosinophils part of a complete blood count?

Yes, eosinophils are one of the five white blood cell types reported in the differential of a complete blood count (CBC).

What is a normal eosinophil count?

Eosinophils normally make up only a small part of your white blood cells; the absolute count in adults usually lies roughly below 0.5 x 10⁹/l. The exact reference range is shown on your own result.

Does a raised eosinophil count always mean an allergy?

No. An allergy or asthma is a common cause, but a raised count can also fit with a parasitic infection, skin conditions or other causes. Your doctor assesses the value together with your symptoms and history.

Does the eosinophil count fluctuate with the season?

Yes, in people with a pollen allergy the eosinophil count can be higher during the pollen season, for example. That is why the timing of the measurement and exposure to triggers matter in the assessment.

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