[The effect of Hashimoto's thyroiditis on the diagnostic efficacy of ultrasound-guided fine needle aspiration cytology for thyroid nodules ≥ 1 cm].

To explore the diagnostic efficacy of ultrasound-guided fine needle aspiration cytology（US-FNAC） for thyroid nodules ≥1 cm, and the effect of Hashimoto's thyroiditis（HT） on it. The clinical data of 1027 cases of thyroid nodules ≥ 1 cm were retrospectively analyzed. Two-dimensional ultrasound, US-FNAC and BRAFV600E gene testing were performed. The postoperative pathological results were used as the criterion. The two dimensional ultrasound examination, clinical characteristics, follow-up results, and BRAFV600E were used to diagnosis for unoperated patients. The diagnostic efficiency of US-FNAC in HT（+） group and HT（-） group was compared, and the factors affecting the diagnostic efficiency were analyzed. Of the 1027 nodules, the cytological results were nondiagnostic/unsatisfactory in 73 nodules（7.1%）, benign in 282（27.5%）, atypia of undetermined significance/follicular lesion of undetermined significance in 230（22.4%）, follicular neoplasm/suspicious for a follicular neoplasm in 20（1.9%）, suspicious for malignancy in 120（11.7%）, and malignant in 302（29.4%）. 515 cases underwent surgery. Among them, 495 were malignant and 20 were benign. 512 cases continued to be followed up without surgery, and the BRAFV600E of them were wild type. Combined with the two dimensional ultrasound examination, clinical features, and follow-up results, they were judged to be benign. The accuracy, sensitivity, specificity, positive predictive value, negative predictive value, false positive rate and the false negative rate the of US-FNAC were 98.7%, 98.4%, 99.3%, 99.5%, 97.5%, 0.7% and 1.6%, respectively. The accuracy, sensitivity and negative predictive value of the HT（+） group were 95.5%, 95.4% and 82.8%, respectively, which were lower than that of HT（-） group （99.5%, 99.4%, 99.2% ）（=0.001, 0.018, <0.001）. The false negative rate of the HT（+） group was 4.6%, higher than 0.6% of the HT（-） group（=0.018）, and HT was an risk factor for increased FNR（=7.596, 95%: 1.452-39.740）. US-FNAC is an effective method for the diagnosis of thyroid nodules and it has high sensitivity and specificity in ≥ 1 cm nodules. However, the combination of HT reduces the diagnostic accuracy and HT is a risk factor for increased false negative rate.