Background: Fine needle aspiration (FNA) cytology is a key investigation of thyroid nodules. There are several reports of FNA accuracy, which ranges from 75.0% to 94.8%, while false negative rates are 5.8% to 21.5%. In Thailand, there is no available data of FNA accuracy according to the Bethesda System for Reporting Thyroid Cytopathology (TBSRTC). The present study reported single-institute data of FNA accuracy, that could be used in thyroid nodule management.

Objective: To determine the diagnostic accuracy of FNA cytology results of thyroid nodules collected in Thammasat University (TU) Hospital.

Materials and Methods: The present study was a retrospective study collected cytologic results of all thyroid nodules that subsequently had definitive histopathologic diagnoses. The data were gathered from clinics at TU Hospital that performed thyroid nodule FNA between May 2011 and November 2014. The FNA cytology results were classified according to TBSRTC. Each cytopathologic result was compared with its postoperative tissue histopathology. The malignancy rate, sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy were calculated.

Results: The present study included 197 thyroid nodule FNA cytology results. The sensitivity and specificity were 77.8% and 65.4%, respectively. The calculated PPV was found to be 47.7%, and the NPV was 87.9%. The accuracy of these results was 69.0%. The malignancy rate of the unsatisfactory group was 6.25%, benign group 8.05%, atypia of undetermined significance or follicular lesion of unknown significance 22.22%, follicular neoplasm/suspicious for follicular neoplasm 14.20%, suspicious for malignancy 73.68%, and malignant 100%.

Conclusion: The FNA cytology in TU Hospital has comparable sensitivity to the other studies. Interestingly, the malignancy rate in the follicular neoplasm category is lower than that of the other institutes because of a high false positive rate in this category. This causes lower specificity and accuracy, which may cause a higher rate of unnecessary operations.

Keywords: FNA; Thyroid nodule; Diagnostic accuracy

DOI: doi.org/10.35755/jmedassocthai.2021.10.13053

Received 31 May 2021 | Revised 23 August 2021 | Accepted 24 August 2021