Fine-needle aspiration cytology (FNAC) is the most important test for a thyroid nodule. Here is what to expect and how the result guides treatment.
What is FNAC?
FNAC is an outpatient procedure where a very thin needle samples cells from a thyroid nodule under ultrasound guidance. It is usually well-tolerated and takes only a few minutes.
Why it is done
To determine whether a nodule is benign, suspicious or malignant — and therefore whether observation, repeat sampling, or surgery is the right next step.
The Bethesda system
Results are reported on a six-category scale (Bethesda I–VI), each linked to a risk of malignancy that drives the recommended action.
After the test
Mild bruising is normal. Results are usually available in 3–5 working days and discussed in a follow-up consultation.
Limitations
Up to 10% of samples may be non-diagnostic and need repeat. Some follicular lesions can only be definitively classified after surgery.