- 01Low while well vs low while ill
A low eosinophil count on a routine test in someone who feels well almost always reflects cortisol (a morning draw, a steroid, stress or exercise) and means nothing; the same number in someone acutely ill is a clue toward infection or sepsis and belongs with the rest of the clinical picture.
A low or zero eosinophil count is almost always harmless in someone who feels well. Eosinophils, the white cells that handle allergy and parasites, make up only 1 to 4% of your white count, so a healthy blood sample can hold very few of them. Their level in the blood follows cortisol, the body's stress hormone: anything that raises cortisol or mimics it, such as a steroid medicine, moves eosinophils out of the blood within hours 1.
The marker this page is about
Where your number falls
Absolute eosinophils: an example low resultcells/uL
What your number means: 0, 10, 40, 0.1 and 1%
Reports print eosinophils in three units that mean the same thing: cells/uL, x10^9/L and K/uL. 100 cells/uL equals 0.1 x10^9/L equals 0.1 K/uL. So an eosinophil result of 0.1 is in range on most reports, and a result of 0.0 means fewer than about 50 cells/uL were counted. A count of 0 means the analyser found too few eosinophils in that small sample to report a number. Most of your eosinophils live in tissues such as the gut and skin, not in the blood, and they are still there. The lab units guide explains these units for every marker.
| Result on the report | Same in cells/uL | What it usually means |
|---|---|---|
| 0 or 0.0 x10^9/L | Under about 50 | Too few to count in this sample; common after steroids, stress or a morning draw |
| 0.01 to 0.03 x10^9/L | 10 to 30 | Low on most lab ranges; usually harmless in someone who feels well |
| 0.04 to 0.05 x10^9/L | 40 to 50 | Borderline; inside range at labs that start at 0 or 30 |
| 0.1 to 0.5 x10^9/L | 100 to 500 | Normal range |
| 1% (percentage line) | Depends on the white count | Read the absolute line instead; 1% of a 5.0 white count is 50 cells/uL |
The absolute count is the white blood cell count multiplied by the eosinophil percentage. A white count of 5.0 x10^9/L with 1% eosinophils gives 0.05 x10^9/L, or 50 cells/uL. A low percentage with a normal absolute count usually means another cell type rose, so the absolute line is the one to trust. The same method gives the absolute neutrophil count, which the calculator below works out from your report.
CalculatorAbsolute neutrophil count calculatorSame white count times percentage method; use it to check any absolute line on your CBC.Work it out Why are my eosinophils low? Common reasons for decreased eosinophils
Most decreased eosinophil counts come down to cortisol. Blood eosinophils follow a daily rhythm that mirrors it: cortisol peaks in the early morning, and eosinophils sit near their lowest then and climb toward night. A routine 8 am draw catches them near their daily low.
- Steroids: prednisone tablets, a steroid injection or high-dose inhaled steroids lower eosinophils within hours, mostly by moving them out of the blood 1. After a single dose the count usually recovers within a day or so.
- Asthma or eczema biologics that target eosinophils, such as benralizumab and mepolizumab, lower counts sharply by design; benralizumab can take them close to zero.
- Acute stress, surgery, a bad night or a painful injury raise cortisol and can lower eosinophils for a day or two.
- Hard exercise in the hours before the test can lower eosinophils for several hours.
- An acute bacterial infection or sepsis, which is why a low count gets more attention in someone who is ill 2.
- Labour and late pregnancy, when cortisol runs high.
Check this beside it
When a low count means something
A low eosinophil count earns attention when you are unwell. In one intensive-care study of 177 patients, a count below 50 cells/uL on admission picked out about 8 in 10 of those with sepsis (a body-wide reaction to infection), and it was low in only about 1 in 11 of those without infection 2. Doctors use that as one clue among many; a low count alone cannot confirm or rule out infection.
The other cause worth knowing is too much cortisol over months, as in Cushing's syndrome. The blood count then shows a stress pattern that does not go away: neutrophils high, lymphocytes and eosinophils low. As our Cushing's page puts it: "The most common cause is prescribed steroid medication such as prednisone, not an internal tumor."
The stress pattern: read this with it
Read it with the rest of your CBC
A low eosinophil count with high neutrophils (the main bacteria-fighting white cells) and low lymphocytes (the white cells behind antibodies and viral defence) points to stress, steroids or infection. A low eosinophil count with a low total white count raises a different question, about why all white cells are down; the low neutrophils page covers that. The CBC guide walks through every line, and lab report flags explains what an L next to a number means.
Same report, next line to check
Can you live with almost no eosinophils?
Yes, as far as current evidence shows. A review of people with very few or no eosinophils, including patients on eosinophil-depleting drugs, found no consistent health problem caused by their absence 4. In asthma patients given benralizumab, a drug that drives blood eosinophils close to zero, for up to five years, serious infection rates stayed in line with earlier studies and side effects did not rise with longer use 5.
Several lines of evidence suggest that deficiency of eosinophils is not associated with any characteristic abnormality.
Where low eosinophils change a treatment decision
If you have COPD (chronic obstructive pulmonary disease, a long-term lung disease usually linked to smoking), the GOLD report, the main international guideline, uses your eosinophil count to guide a steroid inhaler: below 100 cells/uL, adding one is unlikely to help, and 300 cells/uL or more predicts the most benefit 3. This is a decision for your doctor to make with your full history; do not stop or change an inhaler because of one blood result. If you have asthma and use a steroid inhaler, a low count can mean the airway inflammation is under control.
Do I need to raise them? What to do next
No. No diet or supplement has evidence for raising eosinophils, and a low count in a well person needs no fix. If you take a prescribed steroid (tablets, injection or inhaler), do not stop or change it because of this result; ask the prescriber if you have questions. Useful next steps:
- 1Note the contextWrite down the time of the draw, any steroid in the past week (tablets, injections, inhalers, creams over large areas), recent illness and hard exercise. Tell whoever ordered the test about any steroid, since it explains the result.
- 2Read the rest of the CBCIf the white count, neutrophils and lymphocytes are normal, a low eosinophil count on its own is very rarely a concern.
- 3Ask whether a recheck is neededAsk the clinician who ordered the test. If they want one, repeat at the same time of day and the same lab; the blood test prep guide covers timing, and trends beat single readings explains why the second number counts more.
- 4Get care if you are unwellIf you have a fever or feel ill, follow the warning above.
Citations
- Wechsler ME, Munitz A, Ackerman SJ, et al. Eosinophils in health and disease: a state-of-the-art review. Mayo Clin Proc. 2021;96(10):2694-2707.
- Abidi K, Khoudri I, Belayachi J, et al. Eosinopenia is a reliable marker of sepsis on admission to medical intensive care units. Crit Care. 2008;12(2):R59.
- Global Initiative for Chronic Obstructive Lung Disease. GOLD 2025 Report: Global Strategy for Prevention, Diagnosis and Management of COPD.
- Gleich GJ, Klion AD, Lee JJ, Weller PF. The consequences of not having eosinophils. Allergy. 2013;68(7):829-835.
- Korn S, Bourdin A, Chupp G, et al. Integrated safety and efficacy among patients receiving benralizumab for up to 5 years. J Allergy Clin Immunol Pract. 2021;9(12):4381-4392.e4.
Educational context only, not medical advice or a diagnosis. Always discuss your results with a clinician.
