Higher adequacy rates for thyroid aspirates: impact of long-term implementation of modified Bethesda adequacy criteria on aspiration and Afirma performance.

INTRODUCTION: Previous studies suggest that the adequacy rate of thyroid aspirates can be improved by modifying the adequacy criteria of the Bethesda System without loss of sensitivity. We sought to measure the impact of long-term implementation of these criteria. MATERIALS AND METHODS: Results from the long-term implementation of modified Bethesda adequacy criteria (2024-2025) were compared with the initial implementation (2018-2023). Adequacy was classified as Nondiagnostic, Scant but Adequate, or Adequate. RESULTS: Long-term use of the modified Bethesda adequacy criteria resulted in a significantly lower nondiagnostic rate (110 of 2812, 4%) compared with the initial implementation period (506 of 5147, 10%, P < 0.001). Overall, the suspicious rate for Afirma for Adequate cases (317 of 1492, 21%) was significantly higher than for Scant but Adequate cases (82 of 495, 17%, P = 0.02), and the insufficient rate for Afirma in Adequate cases (59 of 1492, 4%) was significantly lower than that for Scant but Adequate cases (53 of 495, 11%, P < 0.001). The risk of malignancy was lower for the Adequate cases (49 of 165, 30%) compared with the Scant but Adequate cases (17 of 36, 47%, P = 0.04). The percentage of cases requiring repeat aspiration (Nondiagnostic cases plus Scant but Adequate cases with insufficient results on Afirma) decreased significantly with long-term implementation (526 of 5147, 10% versus 143 of 2812, 5%; P < 0.001). CONCLUSIONS: Long-term implementation of modified Bethesda adequacy criteria can significantly lower nondiagnostic and repeat aspiration rates without lowering sensitivity. There are significant differences in how Afirma performs in Scant but Adequate cases compared with Adequate cases.