Influence of iodine intake on the diagnostic power of fine-needle aspiration cytology of the thyroid gland.

In order to determine whether the iodine intake influences the diagnostic power of ultrasound-guided fine-needle aspiration cytology (US-FNAC), patients with nontoxic nodular goiter from an area with sufficient iodine intake (IS) (n = 938, median iodine excretion [MIE] = 103 microg/L) and from an iodine-deficient (ID) area (n = 3,601, MIE = 75 microg/L) were investigated. Elevated rates of multinodularity (59.6% vs. 49.6%, p < 0.001), nonpalpable nodules (47.6% vs. 37.3%, p < 0.001) and nondiagnostic US-FNACs (8.8% vs. 5.1%, p = 0.008), and a lower malignancy rate (1.2% vs. 2.3%, p = 0.006) were found in the ID area. Follicular tumors were encountered among positive findings. Cytohistologic comparison (ID, n = 416; IS, n = 97) revealed that the sensitivity, specificity, and diagnostic accuracy of US-FNAC were similar in the two areas (95.5% vs. 92.3%, 78.3% vs. 71.1%, 82.4% vs. 80.6%, IS vs. ID area, respectively), while a lower malignancy rate and a higher ratio of benign to malignant tumors were observed in the ID than in the IS area (10.1% vs. 22.6%, p < 0.001, and 4.38 vs. 1.50, p < 0.001, respectively). This resulted in a lower positive predictive value of US-FNAC in the ID (36/106) than in the IS area (21/36, p = 0.001), because the rate of false US-FNAC was higher in benign (67/184) than in malignant tumors (4/61, p < 0.001).