Fine-Needle Aspiration (FNA) Procedure and Uses - Complete Guide to Lump Testing in Dogs and Cats

ImmunityQ&AMeongsiljang Veterinary Advisory Board

We’ve put together a clear, pet-owner-friendly overview of the procedure, uses, and precautions for fine-needle aspiration of skin lumps or lymph nodes in pets.

What is Fine-Needle Aspiration (FNA)?

A puppy undergoing a fine-needle aspiration test

Fine Needle Aspiration (FNA) is a precise diagnostic procedure in which a thin needle is used to extract a small sample of cells from a lump or lymph node for microscopic examination. The key advantage is that it can be completed in just a few minutes without the need for anesthesia. It serves as the primary diagnostic test to initially determine whether a skin tumor is benign or malignant, or to identify the cause of lymph node swelling.

When is this test needed?

This is the first thing to consider when you feel a new lump on your pet’s body or notice that the lymph nodes are swollen and firmer than usual. We can examine not only visible lumps on the skin but also lesions located deep within the abdomen, lungs, or spleen using ultrasound or CT guidance. This approach plays a crucial role in identifying malignant tumors, where early detection is vital.

Common Situations Requiring Testing

If any of the following situations apply, it’s a good idea to consult with your veterinarian about a fine-needle aspiration (FNA) test.

Situation	Need for Testing
Newly appeared skin lump (1 cm or larger)	High
Rapidly growing mass	Very high
Firmly swollen lymph node	High
Organ lesion detected on ultrasound	High
Long-standing small sebaceous cyst with no changes	Low
Pre-surgical confirmation of tumor nature	Very high

How is the actual examination performed?

The examination process is simpler than you might expect. - Positioning: The owner or technician gently restrains the pet. - Disinfection: The hair in the area to be examined is trimmed slightly, and the skin is disinfected. - Aspiration: A fine needle (22–25G) is inserted to aspirate cells. - Smear: The cells are spread thinly onto a slide. - Staining and Interpretation: After staining, a veterinary pathologist examines the sample under a microscope. If your pet is cooperative, the entire procedure takes only 5 to 10 minutes.

Preparing a slide smear after needle aspiration

Consider alternative tests instead of FNA in these cases

Not all lumps are diagnosed via fine-needle aspiration. We avoid this procedure and opt for alternative tests in cases such as thrombocytopenia or coagulopathies that increase bleeding risk, lung lesions where pneumothorax is a concern, or certain urothelial tumors where needle tracks could potentially spread cancer cells. This is why we first assess safety with basic blood work before proceeding.

Comparison of Fine-Needle Aspiration and Biopsy

Both tests are used to diagnose tumors, but they differ in nature. Fine-needle aspiration is a quick and simple first-line test, while a biopsy serves as a secondary test for a more definitive diagnosis.

Fine-Needle Aspiration vs. Biopsy

Item	Fine needle aspiration (FNA)	Biopsy
Anesthesia	Usually none	Local or general anesthesia
Time required	5–10 minutes	30 minutes or more
Sampling method	Aspirating cells with a needle	Excising a tissue mass
Diagnostic accuracy	Moderate to high (reported around 80%, varies by lesion)	Very high (histological confirmation standard)
Time to results	Same day–3 days	5–10 days
Cost burden	Low	Moderate to high

Accuracy can vary greatly depending on the lesion location and the condition of the cell sample.

Points to check at home after the test

Fine-needle aspiration is a minimally invasive procedure that typically requires little to no recovery time, but please keep an eye on your pet for a few things once you’re back home. - Bleeding: Check if there is any persistent bleeding from the site. - Swelling: Make sure the area around the needle puncture isn’t abnormally swollen. - Pain response: Observe whether your pet keeps licking the area or seems uncomfortable. - General condition: Confirm that their appetite and activity level are back to normal. In most cases, pets return to their usual selves within the same day.

What if the results are inconclusive?

Fine-needle aspiration results generally fall into three categories: a clear diagnosis of benign or malignant, confirmation of inflammation or infection, or a "non-diagnostic" result where the cell count is too low or blood contamination makes interpretation difficult. If a non-diagnostic result is obtained, we proceed with a repeat aspiration or a biopsy. This is why you don't need to give up if a definitive diagnosis isn't reached on the first test.

Rapidly growing lumps require immediate testing

A lump that noticeably grows over a few weeks, a mass that ruptures and oozes fluid, or swelling that extends to nearby lymph nodes are all signs that raise the possibility of malignancy. If you notice any of these symptoms, don’t wait for your next scheduled checkup—visit your veterinarian right away for a fine-needle aspiration test.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

Does the child experience significant pain during a fine-needle aspiration biopsy?

The stimulation is similar to that of a routine vaccination shot. For most pets, it’s just a brief flinch, and the discomfort is minimal enough that the procedure can be performed without anesthesia. In fact, most animals tolerate the sample collection well while fully conscious.

How much should I expect to pay for the tests?

While costs vary by clinic, this test is generally more affordable than a biopsy. The exact price depends on the area being examined and the method used for analysis, so please consult your veterinarian for a precise estimate.

Can cats undergo the same tests as well?

Yes, cats are tested using the same principle. However, more sensitive cats may require sedation, and because chest (lung) lesions carry risks of complications such as pneumothorax or bleeding, we approach them more cautiously and utilize techniques like ultrasound guidance.

When can I expect to hear the results?

In-house testing at our clinic provides same-day results, while samples sent to an external veterinary pathologist typically take 2 to 3 days.

Can a diagnosis be confirmed with just one test?

In many cases, lymphoma, mast cell tumors, and lipomas can be diagnosed through fine-needle aspiration cytology. However, additional biopsies may be necessary for grading mast cell tumors or diagnosing sarcomas and certain epithelial tumors.

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References

[1] Raskin RE, Meyer DJ, Small Animal Cytologic Diagnosis: Canine and Feline Disease, 2nd Edition

[2] Cole SG, Fine Needle Aspirates, Textbook of Respiratory Disease in Dogs and Cats

[3] Jackson HA, Marsella R, BSAVA Manual of Canine and Feline Dermatology, 4th Edition