What are eosinophils?
Eosinophils are made for an enemy too large to swallow: worms and other parasites. They attach to the surface and pour enzymes and toxic proteins over it. Those same granules, which stain pink under the microscope and give the cell its name, are also released with allergy. With hay fever, asthma and eczema the immune system sends eosinophils to the nose, the airways and the skin, and the count in your blood rises along. They are scarce, a few percent of your white cells, and the largest part sits in the tissue, especially in the gut wall. The count in your blood follows the stimulus. In the pollen season it sits higher in anyone with hay fever than in winter. A medicine your body reacts to, some antibiotics, painkillers and drugs for epilepsy, lifts the count, as does a worm infection you have brought back from the tropics. And cortisol suppresses it: with acute stress, a severe infection and during a course of prednisone the count falls to almost zero, which is the reason prednisone works so well for asthma and eczema. Your report shows the count in ×10⁹/L, and read it as an absolute count, not as a percentage. Normal is about 0.1 to 0.4 ×10⁹/L, where the labs overlap. The lower end says nothing; it is the upper end that means something.
Why are eosinophils relevant?
Eosinophils are the number that makes allergy visible. Anyone who is tired in spring, has a blocked nose and wonders whether it is a cold or hay fever sees the answer in the differential: with hay fever the eosinophils rise, with a cold the lymphocytes. In asthma the count is moreover a measure of the type: asthma with many eosinophils responds well to inhaled steroids and to new drugs that switch off exactly this cell, and the count in your blood helps with that choice. A second reason is that a high count without allergy is a clue to something you would otherwise miss. A worm infection after a trip often gives no symptoms for months except a slightly raised eosinophil count. A medicine your body reacts to lets the count rise before the rash comes. And the rare cases, an autoimmune disease of the blood vessels or a bone marrow disease in which production goes astray, begin with a count that keeps rising without explanation. A low count is the side you can ignore. Eosinophils are naturally scarce, three of the four labs start their band at zero, and cortisol suppresses the count with every form of stress or illness. A count of zero mainly says that no allergy or parasite is at work at that moment.
Eosinophils reference ranges
What counts beside the number:
- The absolute count, not the percentage
- The season and your symptoms: in the pollen season the count naturally sits higher with hay fever
- Which medicines you started in the past weeks
- Whether you have been in the tropics, and whether you have gut symptoms
- Whether you take prednisone or an inhaled steroid, because those suppress the count
- CRP and the other white cells: an allergy lifts only this cell and leaves CRP normal
Read eosinophils as an absolute count, not as a percentage. The lower end says nothing: zero is ordinary, and prednisone pushes the count towards zero, so a measurement shortly after a course says little about your baseline. In the pollen season the count naturally sits higher in anyone with hay fever; measure outside it if you want to know your usual level.
What Dutch labs actually use
The upper bound runs from 0.4 at Certe to 0.7 at Star-shl, close to a doubling: someone at 0.6 is normal at Star-shl and raised at the other three. At the bottom Clinical Diagnostics stands alone: it is the only one of the four that sets a lower bound above zero for adults, 0.1. A value of 0.05, worrying nowhere, therefore falls outside the range only at Clinical Diagnostics.
0.1 – 0.4×10⁹/L
Between 0 and 0.1 and between 0.4 and 0.7 it depends on the lab, because each sets its limits on its own method and population. Above 0.7 every lab calls it abnormal.
every lab calls 0.1 – 0.4 ×10⁹/L normal. Between 0 and 0.1 and between 0.4 and 0.7 it depends on the lab.
Every age, per lab
| Laboratory | Group | Reference range |
|---|---|---|
| Unilabs(Saltro, Medlon, SHO, Atalmedial)2026 | Above 15 yrs | < 0.5 ×10⁹/L |
| Star-shl2026 | All ages | < 0.7 ×10⁹/L |
| Certe2026 | Women from 18 yrs | 0–0.4 ×10⁹/L |
| Men from 18 yrs | 0–0.4 ×10⁹/L | |
| Clinical Diagnostics2026 | Above 15 yrs | 0.1–0.5 ×10⁹/L |
Each band as the lab publishes it, retrieved in 2026, unless marked otherwise.
Eosinophils high or low: what it means
A low count means nothing. Cortisol suppresses eosinophils with acute stress, a severe infection or during a course of prednisone, and an inhaled steroid for asthma also suppresses the count a little. There is no lower limit that points to a deficiency or a condition. A high count means there is a stimulus, and the question is which. From common to rare: an allergy, in the Netherlands usually hay fever, asthma or eczema, and then the count tracks the season and the symptoms; a medicine your body reacts to, often in the first weeks after starting; and a parasite, especially after a trip to the tropics or with gut symptoms. Rare are an autoimmune disease of the blood vessels and a bone marrow disease, and you recognise those by a count that repeatedly stays far above the band, often above 1.5, without allergy or travel as explanation. Such a count should be investigated, even without symptoms, because eosinophils that stay high for long can damage the heart and the lungs. What you do about it: with an allergy the stimulus is the lever. Anyone who treats their hay fever, with a steroid nasal spray and where needed an antihistamine, or with immunotherapy that winds down the allergy itself, sees the count fall. In asthma a well-adjusted inhaled steroid is the treatment, and a count that stays high is a sign that the inflammation in the airways is not under control. With a medicine the question is whether it can be stopped or replaced, and you discuss that with whoever prescribed it. With a parasite a course is usually enough. Measure outside the pollen season if you want to know your usual level. Set eosinophils beside the total of white cells and the other types, because an allergy lifts only this cell and an infection the others, and beside CRP, which stays normal with an allergy.
What lowers it
Not a finding: cortisol suppresses eosinophils, and zero is ordinary.
| Cause | How often |
|---|---|
| CorticosteroidsPrednisone and, to a lesser degree, an inhaled steroid suppress the count to almost zero; that is exactly why they work for asthma and eczema | Often |
| Acute infection or stressYour own cortisol suppresses the count with a severe infection, an operation or acute stress; after recovery it comes back | Sometimes |
What raises it
There is a stimulus, and the question is which.
| Cause | How often |
|---|---|
| AllergyHay fever, asthma and eczema; the count tracks the season and the symptoms, and falls when the allergy is treated | Often |
| MedicinesSome antibiotics, painkillers and drugs for epilepsy or gout; the count rises in the first weeks after starting, often before there is a rash | Sometimes |
| Parasitic infectionA worm infection after a trip to the tropics, often for months without other symptoms; a course is usually enough | Sometimes |
| Autoimmune diseaseAn inflammation of the blood vessels in which eosinophils play the lead, usually with asthma and symptoms of nerves or skin alongside | Rare |
| Bone marrow diseaseA count that repeatedly stays far above the band without allergy, medicine or travel as explanation; production itself has then gone astray | Rare |
How does an eosinophils blood test work?
- Referral
- Not needed. Eosinophils are in every blood count with differential, and you can have that measured yourself.
- Fasting
- Not needed; the count does not respond to food. It is naturally lowest in the morning and highest in the evening, so measure at a fixed time if you want to compare.
- When
- Outside the pollen season if you want to know your usual level, and not during a course of prednisone, because that suppresses the count to almost zero. If you want to see how strong your hay fever is, measure in season.
- The draw
- One tube of blood from a vein in your arm. The lab counts the white cells and sorts them into five types; CRP can come from the same draw.
- Repeating
- With a high count after four to six weeks, out of season and after stopping a suspect medicine, to see whether it persists. Otherwise once a year.
- Which test
- Eosinophils is in the comprehensive test (€229) and in .
- Where to draw
- You can draw at 250+ locations near you, no referral needed. See the locations
Frequently asked questions
What are eosinophils?
The white blood cells of allergy and parasites. They are made for an enemy too large to swallow, worms, and pour enzymes and toxic proteins over it. Those same granules are released with allergy: with hay fever, asthma and eczema the immune system sends eosinophils to the nose, the airways and the skin. They are scarce, a few percent of your white cells, and the largest part sits in the tissue.
What is a normal eosinophil value?
Between 0.1 and 0.4 ×10⁹/L, where the four labs overlap, and a count of zero is just as good, because three of the four labs start their band there. Read the absolute count, not the percentage. The count follows the stimulus: in the pollen season it sits higher with hay fever, and during a course of prednisone it falls towards zero, so measure outside those if you want to know your usual level.
What does a high eosinophil count mean?
That there is a stimulus. In the Netherlands that is usually an allergy, hay fever, asthma or eczema, and then the count tracks the season and the symptoms. After that come a medicine your body reacts to, often in the first weeks after starting, and a parasite after a trip to the tropics. A count that repeatedly stays far above the band, often above 1.5, without one of those explanations is investigated, even without symptoms.
What does a low eosinophil count mean?
Nothing. Eosinophils are naturally scarce, three of the four labs start their band at zero, and cortisol suppresses the count with every form of stress or illness. Prednisone and an inhaled steroid do the same. A count of zero mainly says that no allergy or parasite is at work at that moment. There is no lower limit that points to a deficiency or a condition.
Is it hay fever or a cold?
The differential gives the answer. With hay fever the eosinophils rise and CRP and the other white cells stay normal. With a cold the lymphocytes rise and the eosinophils stay ordinary, or even fall, because your own cortisol suppresses them. A count that rises every spring and is back in winter is the pattern of hay fever.
Why does the count rise through a medicine?
Because your immune system recognises the medicine as foreign and builds an allergic reaction against it. Some antibiotics, painkillers and drugs for epilepsy or gout do that most often, usually in the first weeks after starting. The eosinophil count often rises before there is a rash or fever, and that makes it an early signal. Whether the medicine needs stopping or replacing, you discuss with whoever prescribed it.
How do I bring my eosinophils down?
By removing the stimulus. For hay fever a steroid nasal spray works, where needed with an antihistamine, and immunotherapy winds down the allergy itself. In asthma a well-adjusted inhaled steroid is the treatment, and a count that stays high is a sign that the inflammation in the airways is not under control. With a parasite a course is usually enough, and with a medicine stopping or replacing is the solution.
When is a high count investigated?
When it repeatedly stays far above the band, often above 1.5, without allergy, medicine or travel as explanation. Then it can be an autoimmune disease of the blood vessels, usually with asthma and symptoms of nerves or skin, or a bone marrow disease in which production goes astray. That is rare, but eosinophils that stay high for long can damage the heart and the lungs, and that is why such a count is not waited out.
Which tests include eosinophils?
Eosinophils is in the Biological age test (€69, also as an add-on for €15), in the comprehensive test (€229) and in .
Related biomarkers
Sources
- 1.Unilabs, test catalogue (Dutch): white cell differential. 2026. bepalingenklapper.nl
- 2.Star-shl, test catalogue (Dutch): eosinophils. 2026. star-shl.nl
- 3.Certe, test catalogue (Dutch): eosinophil granulocytes. 2026. bepalingenwijzer.certe.nl
- 4.Clinical Diagnostics, lab guide (Dutch): eosinophils. 2026. clinicaldiagnostics.nl
- 5.LESA Laboratory diagnostics (Dutch primary-care laboratory agreement). 2026. richtlijnen.nhg.org
Educational information only, not medical advice. Consult a healthcare professional for clinical decisions.
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