Histologic follow-up of nondiagnostic thyroid fine needle aspirations: implications for adequacy criteria

There is limited histologic follow-up for adequacy criteria in thyroid fine needle aspirations. We correlated the number of benign follicular cells in nondiagnostic aspirates (excluding atypical and Hurthle cells) and the results of histologic follow-up. A total of 170 cases with only benign follicular cells were reviewed. The sensitivity and specificity for 60 benign follicular cells was 97% and 42%. If the threshold for adequacy was lowered to 10 cells, the specificity of a benign diagnosis increased significantly (42% to 50%, P < 0.001) without a significant change in sensitivity (97% to 96%, P = 0.45). An additional 63 cases were diagnosed as adequate with three false negative cases. Lowering the threshold to 30 cells had no change in sensitivity (97%), increased specificity to 45% but this was not significant (P = 0.08). An additional 26 aspirates could be diagnosed as adequate without any false negative cases. Histologic follow-up suggests that the current criteria for adequacy can be lowered to improve specificity while retaining excellent sensitivity.