Updated September 25, 2026. Fact-checked against veterinary sources; review by a licensed veterinarian is in progress. See our editorial policy.
Quick answer: White blood cells fight infection and control inflammation. In cats, abnormal counts are common on bloodwork and have many causes, from stress and inflammation to infections like panleukopenia or FeLV, and less commonly bone marrow disease or leukemia. The meaning depends on which cell type is affected, how abnormal it is, and how your cat is feeling. Your vet will interpret results alongside an exam and may repeat the test.
Types of white blood cells
- Neutrophils: the first responders to bacterial infection and inflammation
- Lymphocytes: part of the immune memory system (see high or low lymphocytes in cats)
- Eosinophils: involved in allergies and parasite responses
- Monocytes: clean up debris and respond to chronic inflammation
High neutrophils (neutrophilia)
- Stress or excitement at the clinic, or steroid medication
- Inflammation or infection, such as abscesses, pyothorax, or pancreatitis
- Tissue damage or tumors
Low neutrophils (neutropenia)
- Feline panleukopenia: a severe viral infection in unvaccinated cats and kittens
- FeLV or FIV
- Overwhelming infection, when neutrophils are used up faster than they’re made
- Chemotherapy and some other drugs
- Bone marrow disease
A very low neutrophil count raises infection risk. Cats with fever, lethargy, or vomiting and low neutrophils need urgent care.
High eosinophils (eosinophilia)
- Fleas and intestinal or lung parasites
- Allergies, including food and environmental allergies
- Feline asthma
- Eosinophilic granuloma complex (skin or lip lesions)
- Rarely, certain cancers or hypereosinophilic syndrome
Leukemia
Rarely, very high or abnormal-looking white blood cells are due to leukemia or lymphoma in the blood. Specialized tests like a blood smear review, flow cytometry, or bone marrow sampling help confirm it.
Typical next steps
- Repeat the blood count, sometimes after a few days or weeks
- A blood smear review by a pathologist
- FeLV and FIV testing
- Chemistry panel, urinalysis, and thyroid level
- Parasite testing and flea control
- Chest X-rays or abdominal ultrasound
- Bone marrow sampling if counts stay abnormal without a clear cause
When to call your vet
Call promptly if your cat has fever, lethargy, not eating, vomiting, diarrhea, breathing changes, or weight loss, especially after abnormal blood results.
What to avoid
- “Immune booster” supplements as a substitute for diagnosis.
- Leftover antibiotics.
- Delaying vaccination in kittens, since panleukopenia can be fatal.
Frequently asked questions
Can stress change my cat’s white blood cell count?
Yes. Stress can raise neutrophils and, in some cats, lymphocytes, and lower eosinophils.
Does an abnormal count mean cancer?
Usually not. Inflammation, infection, parasites, and stress are much more common causes.
Can diet fix white blood cell problems?
No. The count reflects an underlying cause, which needs to be found and treated.
Sources
- Merck Veterinary Manual: Leukocyte disorders in animals
- Cornell University College of Veterinary Medicine eClinPath: Leukocyte changes
- Merck Veterinary Manual: Feline panleukopenia
- Little SE, et al. 2020 AAFP Feline Retrovirus Testing and Management Guidelines. J Feline Med Surg. 2020
This article is for general education and is not a substitute for care from your own veterinarian. Learn about The Pet Vet and our editorial policy.