Updated September 25, 2026. Fact-checked against veterinary sources; review by a licensed veterinarian is in progress. See our editorial policy.
Quick answer: A fine needle aspirate (FNA) is a quick, low-risk test in which a vet uses a small needle to collect cells from a lump, lymph node, or organ, then examines them under a microscope (cytology). It’s usually done in the exam room without sedation, often gives an answer within minutes to a few days, and can tell harmless fatty lumps from ones that need removal. Sometimes it can’t give a clear answer, and a biopsy is recommended.
When vets recommend an FNA
- New lumps or bumps on or under the skin
- Lumps that are growing, changing, or bothering your pet
- Enlarged lymph nodes
- Abnormal organs or masses found on ultrasound
- Fluid-filled swellings
Veterinary cancer specialists advise checking any lump that is the size of a pea or larger and has been present for a month. Lumps can’t be diagnosed by look or feel alone.
What happens during the procedure
- Your vet holds the lump steady and inserts a fine needle, sometimes several times in different spots.
- Cells are pushed onto glass slides and stained.
- Your vet may look at the slides in the clinic, or send them to a veterinary pathologist.
It takes a few minutes. Most pets tolerate it like a vaccination. Sedation may be used for sensitive areas, anxious pets, or organ samples guided by ultrasound.
Possible results
- Benign: such as a lipoma (fatty lump) or cyst. Your vet may recommend monitoring.
- Inflammation or infection: such as an abscess or reaction to a bite or insect sting.
- Cancer: such as a mast cell tumor or lymphoma. This guides next steps, like surgery planning or further tests.
- Non-diagnostic: not enough cells, or unclear results. A repeat FNA or biopsy may be needed.
FNA vs. biopsy
An FNA looks at individual cells. A biopsy removes a piece of tissue, which shows how cells are arranged and can grade tumors. Biopsies are more invasive but more definitive, and they’re recommended when an FNA isn’t conclusive or when the grade affects treatment.
Risks
- Minor bruising or bleeding at the site
- Rarely, a mast cell tumor can swell or redden after being handled. Your vet may give an antihistamine first if one is suspected.
- Organ aspirates carry a small risk of bleeding, so clotting tests may be done first.
Aftercare
- Most pets need no special care.
- Watch for swelling, bleeding, or discomfort, and call your vet if they appear.
- Keep a record or photo of the lump’s size and location so changes are easy to track.
What to avoid
- Assuming a soft lump is “just fat” without testing. Some cancers feel soft.
- Squeezing or popping lumps at home.
- Waiting if a lump grows quickly, changes, ulcerates, or bleeds.
Frequently asked questions
Does a fine needle aspirate hurt?
It causes brief discomfort, similar to a vaccine. Most pets don’t need sedation.
How long do results take?
Some results are available during the visit. Samples sent to a pathologist usually take a few days.
Can an FNA spread cancer?
The risk is considered extremely low for most tumors, and the benefit of knowing what a lump is far outweighs it. Your vet may choose a different approach for certain tumor types.
Sources
- Merck Veterinary Manual: Cytology
- Veterinary Cancer Society: See Something, Do Something campaign
- Merck Veterinary Manual: Mast cell tumors
- AAHA Oncology Guidelines for Dogs and Cats. 2016
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.