Fine needle aspiration cytology is a procedure that uses a small, hollow needle to gently puncture the skin into a lesion to obtain a small sample of cells or fluid from a tumor or an organ under the skin for testing, to determine whether the lesion is benign or malignant.

Fine needle aspiration cytology, or FNA for short, applied in diagnosing thyroid nodules is considered the most effective method due to its accuracy of over 95%; with a positive predictive value of 89-98%, a negative predictive value of 94-99%; and false negative and false positive rates of less than 1%. FNA has helped select the right cases requiring surgery, reducing the number of cases requiring surgery by more than half, which means reducing treatment costs.