Blood count and blood group · Blood

Eosinophils

A type of white blood cell that rises mainly with allergies and parasites; part of the extended blood count.

At a glance

Measured in blood
In 5 test panels
No special preparation

Explanation

Eosinophils: what is measured?

Eosinophils (eosinophilic granulocytes) are one of the five types of white blood cells. They play a role in the defense against parasites and in allergic reactions. The laboratory counts them as part of the white blood cell differential (the breakdown of white blood cells into types) and gives the number per liter of blood, often also as a percentage of all white blood cells. Normally the number is low.

What can it detect?

Allergic conditions such as hay fever, asthma and eczema
Infections with parasites, for example worms
Reactions to medicines
Rare conditions with strongly raised eosinophils, such as hypereosinophilic syndrome or certain blood diseases

Result

What does the result mean?

Eosinophils too high

A raised number of eosinophils (eosinophilia) usually fits an allergy, for example hay fever, asthma or eczema, or an infection with parasites, such as worms after a trip to the tropics. A reaction to medicines can also raise the number. A slightly raised value without symptoms is often harmless and disappears on a repeat measurement. A strongly and persistently raised number is rare and may point to an autoimmune disease, hypereosinophilic syndrome or a blood disease; symptoms that go with this are a skin rash, shortness of breath, abdominal symptoms or tiredness.

Eosinophils too low

A low number of eosinophils almost never has any meaning. The number is naturally low and in healthy people can even be zero in a count. Corticosteroids (anti-inflammatory drugs such as prednisone), stress and an acute infection lower the number temporarily. A low value on its own does not call for follow-up tests.

After an abnormal result

With a slightly raised number, the GP usually repeats the count after a few weeks and asks about allergies, medicines and travel. With a strongly or persistently raised number, tests for the cause follow, such as a stool test for parasites, and if needed a referral to an internist.

Reliability

How reliable is the test?

The number of eosinophils is part of the blood count and on its own is not a test for any particular disease. According to the Dutch Society for Clinical Chemistry (NVKC), a raised value points to involvement of the immune system, but the value does not say which allergy or infection is the cause. A slightly raised number is often temporary; its meaning depends on symptoms, travel history, medicine use and a repeat measurement.

What can affect the result?

Corticosteroids (for example prednisone), acute stress and an acute infection lower the number and can mask eosinophilia.
The number varies over the day and with exposure to allergens such as pollen; a single measurement is a snapshot.
With a small number of cells the count is less accurate; laboratories differ in reference values and in reporting as a percentage or as an absolute number.
A normal number of eosinophils does not rule out an allergy; many people with hay fever have a normal blood count.

Who it is for

Who is the test useful for?

Useful for

Useful as part of an extended blood count with symptoms that fit an allergy, asthma or a parasitic infection, for example a skin rash, shortness of breath or abdominal symptoms after a trip to the tropics, and with unexplained long-lasting symptoms. As a stand-alone test it has little value. In adults without symptoms, routine measurement is not needed, and for diagnosing a specific allergy an allergy test (specific IgE) is more suitable.

How common is it?

Allergic conditions are common in the Netherlands: in 2024 about 600,000 people were receiving care for asthma, and hay fever and eczema are also common. A slightly raised number of eosinophils is therefore a common finding. A strongly raised number due to a blood disease or hypereosinophilic syndrome is rare.

VZinfo (RIVM), asthma figures 2024

Drawbacks and risks

A slightly raised number of eosinophils is common and usually harmless; without context it can lead to unnecessary worry and extra tests.

Get tested

Eosinophils: test panels

Eosinophils is part of these test panels. You order online and have your blood drawn at a collection point or collect the sample at home.

Blood draw
Complete Blood Count (CBC)
Complete Blood Count Extended; standard blood count plus detailed white blood cell analysis.
€ 27,00
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Whoop (Advanced Labs)
Comprehensive blood analysis with biomarkers that integrates directly with your WHOOP wearable for optimal performance and recovery.
€ 385,00
Fingerstick
Full blood count with differential (CBC) (finger-prick)
Full blood count including haemoglobin, platelets and a white cell differential.
€ 27,00

How reliable is the test?

Eosinophils