FrançaisWhat eosinophils are
Eosinophils are white blood cells with red-staining granules. They take part in allergic reactions and in the defence against parasites, especially those that migrate through tissues [1].
On the report, the eosinophil line (EOS) appears in the differential, as a percentage and as an absolute count. Eosinophilia and eosinopenia are defined on the absolute count: a percentage can rise only because other white cells have fallen [1].
| Species | Eosinophils, example interval |
|---|---|
| Dog | 0–9% of white cells |
| Cat | 0–4% of white cells |
How to read the eosinophil line
Here is an example line from a dog’s differential.
- Abbreviation EOS or eosinophils, sometimes followed by “#” for the absolute count and “%” for the percentage.
- Result 2.4 × 10³/µL in this illustrative line: an eosinophilia.
- Unit 10³/µL, 10⁹/L or G/L: the same number in all three.
- Laboratory interval An illustrative laboratory interval; each laboratory sets its own.
- Flag H: above the interval. Your vet looks for allergies and parasites first [1].
Causes of high eosinophils
- Allergies and hypersensitivity. Common, for example allergic skin disease [1].
- Parasites. Common, especially external parasites and parasites with a migrating tissue stage. Heartworm is a common cause in dogs. Most blood parasites do not cause eosinophilia [1].
- Tumours. Some tumours stimulate eosinophil production, most often mast cell tumours, and also some lymphomas and carcinomas [1].
- Addison’s disease. The lack of cortisol can cause a usually mild eosinophilia in dogs [1]; it is checked with an ACTH stimulation test.
- Hypereosinophilic syndrome. A rare, persistent, moderate to marked eosinophilia with no cause found, reported in Rottweilers and in cats [1].
- Eosinophilic leukemia. Rare [1].
In a Swedish study of 105 dogs with a marked eosinophilia (above 2.2 × 10⁹/L), 36% had inflammatory disease of the gut, lungs or skin, 12% had eosinophilic lung disease and 11% had mange or nasal mites. The increase was often transient, and Rottweilers were over-represented [3].
Low eosinophils
A low eosinophil count is most often due to cortisol, from stress, illness or a corticosteroid medicine, as part of the stress pattern. It can also be seen with acute inflammation, particularly sepsis. Because the interval often starts at zero, a low count is hard to document [1].
In a sick dog, a normal or high eosinophil count where a stress pattern would be expected can be one reason to consider Addison’s disease [1].
What your vet may check next
A persistent, unexplained eosinophilia may lead to imaging or sampling of a mass or lymph node. For the full CBC, see CBC blood test for dogs and cat blood work explained.
En français : éosinophiles du chien et du chat.
Questions to ask your veterinarian
- Is the absolute eosinophil count high, or only the percentage?
- Which parasite tests should we do, including heartworm?
- Could an allergy explain the result?
- Should we repeat the count after treating parasites or an allergy?
- If it persists, what are the next steps?
Get your pet’s full blood count explained, line by line.
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Frequently asked questions
What does a high eosinophil count mean in a dog?
Most often an allergy or parasites, including heartworm. Less often a mast cell tumour or lymphoma, Addison’s disease or a hypereosinophilic syndrome [1].
What does a high eosinophil count mean in a cat?
Allergies and parasites are the main causes, as in dogs. Some tumours and a rare hypereosinophilic syndrome are other causes [1].
Can high eosinophils go back to normal?
Often yes, once the parasite is treated or the allergy is controlled. Your vet may recheck the count after treatment.
What eosinophil count is alarming?
There is no single number. A moderate to marked increase that persists without a cause is investigated further, especially with other abnormal results. Marked increases are often transient [1, 3].
Why are my pet’s eosinophils low?
Usually stress or a corticosteroid medicine. A low count on its own is rarely a concern [1].
Sources
- eClinPath, Cornell University College of Veterinary Medicine. Leukocytes. eclinpath.com/hematology/leukogram-changes/leukocytes
- Merck Veterinary Manual. Hematology (complete blood count) reference ranges. merckvetmanual.com/reference-values-and-conversion-tables/reference-guides/hematology-reference-ranges
- Lilliehöök I et al. Diseases associated with pronounced eosinophilia: a study of 105 dogs in Sweden. J Small Anim Pract. 2000;41(6):248-253. doi.org/10.1111/j.1748-5827.2000.tb03934.x
Laboratory methods and reference intervals vary. This article explains; it does not diagnose. For a decision about your pet, use the original report and talk to your veterinarian. Our editorial policy.