Found a Lump on Your Dog or Cat? What to Expect From a Fine Needle Aspirate
Verified by: Luisa Kumeta
Published on: 25 September 2026
Finding a lump on your pet can be worrying, but not all lumps are serious. A fine needle aspirate (FNA) is one of the quickest ways for your vet to find out more. This guide explains what an FNA is, how to prepare your pet at home and what happens once the sample has been taken.
What is a fine needle aspirate?
A fine needle aspirate is when your vet uses a thin needle to collect a small sample of cells. It can be taken from:
- A lump or bump
- A swollen lymph node
- An internal organ
Why has my vet recommended one?
Looking at the cells under a microscope helps your vet work out what might be causing a lump. For example, it could be:
- Inflammation
- An infection
- A fluid-filled cyst
- A benign (non-cancerous) growth
- A tumour
The results help your vet decide on the right treatment straight away or whether further tests are needed.
It's worth knowing that not every lump can be diagnosed with an FNA. It depends on the size, location and type of lump.
How to prepare your pet for a fine needle aspirate
- Take photos and keep a diary. Photograph any lumps you find and keep a record of them, including measurements. This helps your vet see whether a lump has changed over time.
- Leave the lump alone. Keep the area clean and dry, and avoid squeezing, pinching or pressing on the lump.
- Keep your pet calm. FNAs can often be done while your pet is awake, depending on their temperament and the type, size and location of the lump. Keeping your pet calm and rested before the appointment can help.
- Withhold food if your vet asks you to. You may be told not to feed your pet for 6 to 12 hours beforehand. This is usually only needed if your pet will be sedated or given an anaesthetic.
What tests might my vet do?
| Test | What it involves |
|---|---|
| In-house cytology | The cells are placed on a slide, stained and examined under a microscope in the practice for a quick first look |
| External lab cytology | The slides are sent to a specialist veterinary pathologist for a more detailed look and a formal report |
| Culture and sensitivity | If fluid or signs of infection are found, a sample may be grown in a lab to identify the bacteria and choose the right antibiotic |
| Ultrasound-guided FNA | Ultrasound is used to guide the needle accurately when sampling internal organs or deeper lumps |
You can find out more about ultrasound in our guide to preparing your dog or cat for an X-ray or scan.
What happens next?
Results and discussion
Your vet will talk you through the findings once the results are ready. In-house results are often available quickly, while lab reports usually take a little longer.
Biopsy or surgery
If the FNA doesn't give a clear answer, or it confirms a mass, your vet may recommend a surgical biopsy or removing the lump completely.
Medication
In some cases, your vet may recommend medical treatment.
Monitoring
If a lump turns out to be benign, your vet will often recommend keeping an eye on it rather than removing it.
- Preparing for an X-ray or Scan
Some lumps are sampled using ultrasound. Find out how to get your dog or cat ready for imaging and what happens next.
Not sure if it's serious?
That's exactly what we're here for. Send us a video of your pet, any time of day or night, and one of our vets will get back to you within minutes with clear next steps, whether that's home care or a same-day appointment with your practice.