Fine Needle Aspiration (FNA / Cytology)
A quick, minimally invasive diagnostic procedure using a fine needle to collect cells from a lump, organ, or fluid for microscopic cytology.
💬 In Plain English
A fine needle aspiration (FNA) is one of the most useful diagnostic tests in veterinary medicine. When a veterinarian finds a skin lump, enlarged lymph node, or internal organ mass on ultrasound, they gently insert a tiny needle (the same size used for routine vaccines) into the lump. Cells are drawn up into the needle hub, sprayed onto a glass microscope slide, stained, and examined under a microscope (cytology). It is fast, causes minimal discomfort, rarely requires sedation, and provides a quick answer on whether a lump is an innocent cyst, fatty lipoma, infection, or serious cancer like a mast cell tumor.
🔬 Clinical & Technical Depth
For Vets & TechniciansFormal Clinical Definition
Diagnostic micro-biopsy sampling technique utilizing 22-to-25 gauge needles with or without negative-pressure suction to harvest individual cells and micro-fragments for microscopic cytological evaluation. Evaluates cell morphology, criteria of malignancy, infectious organisms, and inflammatory populations.
Why Veterinarians Use It
Veterinarians use FNAs to investigate any new or growing lump before performing surgery, determining whether wide surgical margins or simple monitoring is indicated.
Clinical Context Encountered
Performed routinely in exam rooms during wellness visits for skin nodules, or in the ultrasound suite for liver, spleen, or kidney masses.
Clinical Reference Guide (Surgical Procedure)
- •If a mast cell tumor is aspirated, local histamine release can cause immediate localized swelling and redness (Darier’s sign); an antihistamine may be administered.
❓ Questions to Ask Your Veterinarian
Take these actionable questions with you to your next clinic visit or appointment:
- 1Did the in-house cytology provide a definitive diagnosis (like a lipoma or mast cell tumor)?
- 2Should the slides be mailed to a board-certified veterinary clinical pathologist (DACVP) for expert review?
- 3Was the sample adequately cellular, or was it non-diagnostic (hemodilute or acellular)?
- 4Will a surgical biopsy and histopathology be needed to confirm the grade or architecture?
Academic & Clinical References
- ASVCP Guidelines on Cytology Slide Preparation and Diagnostic SamplingOrganization: American Society for Veterinary Clinical Pathology (ASVCP) • Accessed: 2026-01-10https://www.asvcp.org