# Thyroid FNAC

URL: https://thethyroidologist.com/tests/thyroid-fnac/
Section: Tests
Last medically reviewed: 2025-11-01

> Fine needle aspiration cytology (FNAC) samples thyroid nodule cells to check for cancer. How it works, preparation, and what results mean.

Thyroid fine needle aspiration cytology (FNAC or FNA) is a biopsy procedure that samples cells from a thyroid nodule using a thin needle — guided by ultrasound.
It is the standard test for determining whether a suspicious nodule is cancerous.

## How the procedure works

After cleaning the skin, a thin needle is inserted into the nodule under ultrasound guidance. Cells are aspirated into a syringe and examined under a microscope. The procedure takes a few minutes and causes only mild discomfort — local anaesthesia is often not needed.
Multiple passes may be needed for adequate sampling, especially for larger nodules.

## When FNAC is recommended

FNAC is indicated for nodules meeting size and ultrasound-risk criteria — typically nodules over 1 cm with suspicious features, or smaller nodules with high-risk ultrasound patterns. Purely cystic nodules rarely need biopsy.
It is not needed for every nodule — most small, benign-appearing nodules are monitored instead.

## Understanding results

Results are reported on the Bethesda classification: I (non-diagnostic — repeat may be needed), II (benign), III (atypia of undetermined significance — may need repeat or surgery), IV (follicular neoplasm — surgery usually needed for diagnosis), V (suspicious for malignancy), VI (malignant).
FNAC cannot always distinguish benign from malignant follicular lesions — those require surgical pathology.

## Frequently asked questions

### Is FNAC painful?

Most patients feel only mild discomfort — a brief pinch or pressure. The procedure takes a few minutes and serious complications are rare.

### What if the result is "non-diagnostic"?

Bethesda I means insufficient cells were obtained — the biopsy is usually repeated, sometimes with on-site adequacy assessment.

### Can FNAC miss cancer?

FNAC has a small false-negative rate — ultrasound correlation and clinical judgment matter. Suspicious nodules with benign FNAC may still need monitoring or surgery.

## Disclaimer

The content on this website is for general educational purposes only and does not constitute medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional about your specific condition.

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