Adequacy criteria for thyroid FNA evaluated by ThinPrep slides only

Adequacy criteria for thyroid fine-needle aspiration (FNA) recommended by The Bethesda System for Reporting Thyroid Cytopathology (TBS) were developed with smears, but they are commonly applied to ThinPreps (TPs). This study evaluated adequacy in TPs at different diagnostic thresholds.

All FNA procedures performed between 2010 and 2015 with matched surgical specimens were analyzed. Cell counts and cytological features were evaluated in all initially nondiagnostic (ND) cases. ND cases were reclassified into TBS categories by 2 pathologists, and the results were compared with surgical outcomes.

One hundred forty-six of the 151 cases initially classified as ND were available for review, and they had a mean cell count of 60.5 (standard deviation, 71.4). Interobserver agreement on the reclassification of ND cases was moderate (k = 0.57), and consensus yielded 48 ND cases (33%), 72 benign cases (49%), 24 cases of atypia of undetermined significance (16%), and 2 cases suspicious for malignancy (1%). Lowering the diagnostic threshold to any follicular cells yielded a sensitivity of 92%, a specificity of 60%, a positive predictive value of 59%, a negative predictive value of 92%, and a false-negative rate of 7.7%, whereas the values for the initially diagnostic cases were 93%, 58%, 59%, 93%, and 7.7%, respectively. Including cases with >60 cells but lacking 6 groups containing at least 10 cells did not affect test performance. Nuclear enlargement, pallor, grooves, and the presence of histiocytoid cells in initially ND FNA correlated with malignancy.

In thyroid FNA examined with TP only, lowering the adequacy threshold and eliminating the requirement of 6 groups of at least 10 cells did not significantly affect test performance if cytological features associated with malignancy were absent. Cancer Cytopathol 2017;125:534-43. © 2017 American Cancer Society.