Thyroid FNAC
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.
Last medically reviewed: 1 November 2025
Key points
- FNAC samples cells from a thyroid nodule with a thin needle.
- It is usually performed under ultrasound guidance.
- Results are reported using the Bethesda system.
- Most biopsied nodules are benign.
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.
References & further reading
This page is based on established medical knowledge and guidelines from authoritative sources. Always consult a qualified clinician for personal medical advice.
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