IntroductionFine needle aspiration biopsy (FNAB) is an effective method used in the differential diagnosis of thyroid nodules. The Bethesda system has contributed to the determination of clinical approaches by bringing standardization to cytopathology reporting. However, the rate of cytological-histological incompatibility varies between 10% and 30%. Results differ according to clinics in the literature. These results create a need to reevaluate the efficacy and safety of fine needle aspiration biopsy. In this study, we aimed to evaluate the diagnostic accuracy of FNAB of thyroid nodules by correlating the cytopathology results of FNAB with the results of postoperative histopathology.MethodsIn this retrospective study, thyroid FNAB results and postoperative histopathology results of patients who underwent thyroidectomy operations in our clinic between January 2018 and December 2021 were compared. Accuracy, sensitivity (Sn), specificity (Sp), positive predictive value (PPV), negative predictive value (NPV), false positive rate (FPR), and false negative rate (FNR) were calculated. Cases with nondiagnostic FNAB results were excluded from the calculations. FNAB results with a follicular neoplasm/suspicious for a follicular neoplasm (FN/SFN) and suspicious for malignancy were included in the malignant group.ResultsA total of 304 patients were included in the study. The male/female ratio was 1:3.3. As a result of the study, malignancy was detected histopathologically in 47 (15.46%) patients. The commonest malignancy detected was papillary carcinoma. According to the Bethesda system, the results were evaluated in six categories. The incidence of malignancy in the Bethesda categories were 0%, 4%, 40%, 69.2%, 100%, and 100%, respectively. Accordingly, the specificity and sensitivity of FNAB for detecting malignancy were 98.7% and 66.6%, respectively. The accuracy was 93.5%. The false positive rate, false negative rate, positive predictive value, and negative predictive value were 1.20%, 33.3%, 91.4%, and 93.8%, respectively.ConclusionThyroid FNAB is an effective method used with satisfactory reliability in the differential diagnosis of malignancies of thyroid nodules. Still, it has some limitations. This article demonstrates higher rates of malignancy in Bethesda categories III and IV. Therefore, clinical approaches are gaining importance in these categories.