Updated September 25, 2026. Fact-checked against veterinary sources; review by a licensed veterinarian is in progress. See our editorial policy.
Quick answer: Lymphocytes are a type of white blood cell. In cats, a high lymphocyte count is most often caused by fear or excitement during the vet visit, which temporarily releases lymphocytes into the blood. It can also be caused by young age, inflammation, or infection, and less commonly by lymphoma or leukemia. A low count is most often caused by stress hormones or steroid medication during illness. One abnormal result is a clue, not a diagnosis. Your vet will interpret it alongside your cat’s health and other tests, and often repeat it.
High lymphocyte count (lymphocytosis)
Common causes
- Fear or excitement: a stressed cat at the clinic can have a temporary, sometimes striking, rise. It returns to normal once the cat is calm.
- Young age: kittens and young cats normally have higher counts.
- Recent vaccination or chronic inflammation
- Chronic infections, including some viral or parasitic infections
Less common, more serious causes
- Lymphoma with cancer cells circulating in the blood
- Chronic lymphocytic leukemia
- Addison’s disease (rare in cats)
A count that’s very high, stays high on repeat tests, or comes with abnormal-looking cells, weight loss, enlarged lymph nodes, or anemia needs further testing.
Low lymphocyte count (lymphopenia)
- Stress from illness: the most common cause. Stress hormones lower lymphocyte numbers.
- Steroid medications such as prednisolone.
- Viral infections such as panleukopenia, FeLV, FIV, and FIP.
- Loss of lymph fluid, for example with chylothorax (fluid around the lungs) or some gut diseases.
- Some chemotherapy drugs.
Typical next steps
- Repeat the blood count when your cat is calm, sometimes after a few weeks
- Blood smear review by your vet or a pathologist to look at cell shape
- FeLV and FIV testing
- Chemistry panel, urine tests, and thyroid level
- Imaging (X-rays, ultrasound) to check lymph nodes and organs
- Specialized tests such as flow cytometry or PARR if cancer is suspected
Reducing stress at vet visits
- Leave the carrier out at home so it becomes familiar.
- Cover the carrier with a towel during travel and in the waiting room.
- Ask about cat-friendly clinics and quieter appointment times.
- Ask your vet about anti-anxiety medication before visits for very stressed cats.
When to call your vet
Call if your cat has weight loss, poor appetite, vomiting or diarrhea, swollen lymph nodes, breathing changes, or lethargy, especially after an abnormal blood count.
Frequently asked questions
Does a high lymphocyte count mean my cat has cancer?
Usually not. Stress is the most common cause in cats. Your vet will look at the whole picture and may repeat the test.
Can stress really change blood results?
Yes. In cats, fear can cause a rise in lymphocytes, while longer-term illness-related stress tends to lower them.
Can diet or supplements fix an abnormal count?
No. The count reflects an underlying cause, which is what needs to be identified and treated.
Sources
- Merck Veterinary Manual: Leukocyte disorders in animals
- Merck Veterinary Manual: Lymphoma in cats
- Cornell University College of Veterinary Medicine eClinPath: Lymphocytes
- AAFP/ISFM Cat Friendly Veterinary Interaction Guidelines. J Feline Med Surg. 2022
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.