Eosinophils
Blood count (CBC) ·Also called: EOS, eosinophil count, eosinophilia
What it is
Eosinophils are packed with granules that damage parasite larvae, and they accumulate wherever allergic inflammation is happening — skin, airways, or gut lining. Only a small fraction of the body's eosinophils are in the blood at any time.
Why your vet measures it
Eosinophilia is a genuinely useful pointer, because the list of causes is short and mostly treatable. It is also one of the classic clues to Addison's disease in dogs, where the eosinophil count fails to drop the way a stressed animal's should.
What a high result can mean
- Parasites — intestinal worms, fleas, lungworm, or heartworm
- Allergic skin disease, especially flea allergy dermatitis
- Feline asthma and the eosinophilic granuloma complex in cats
- Hypoadrenocorticism (Addison's disease) in dogs
- Some tumours, notably mast cell tumours and certain lymphomas
What a low result can mean
- Stress, illness or steroid treatment — a normal and expected part of the stress leukogram
Dogs and cats differ
Cats mount eosinophilic responses more readily than dogs and to a wider range of triggers, from asthma to oral eosinophilic lesions. In dogs, a persistently high count with no parasites found makes Addison's disease worth ruling out.
Questions worth asking your vet
- Is my pet up to date with flea and worm treatment, including the parasites this test cannot see?
- Could an allergy explain this, and is a skin or airway problem present?
- In a dog with vague signs and high eosinophils, should we test for Addison's?
Related terms
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