Molecular testing and other metrics in thyroid cytology as quality‐assurance measures in evaluating variation among pathologists in the diagnosis of atypia of undetermined significance

BACKGROUND: Atypia of undetermined significance (AUS) is a subjective diagnosis with reported interinstitutional rates ranging from 1% to 20%. The Bethesda System for Reporting Thyroid Cytology (TBS) endorsed ≤10% as an achievable target; however, lowering AUS rates without informed, adjusted diagnostic thresholds can compromise the sensitivity of thyroid cytology. The authors conducted this study to identify quality-assurance measures that can assess individual pathologist's metrics compared with laboratory averages and published benchmarks and can provide feedback to pathologists on the causes of discrepancy. METHODS: AUS rates of 15 cytopathology-boarded pathologists were correlated with AUS:malignant ratios (AUS:M), histologic risks of malignancy (ROMs), and Afirma molecular-positive call rates (PCRs), and scatterplots were constructed. The distribution of pathologist TBS diagnostic categories was compared with laboratory averages and correlated with the above metrics. RESULTS: Pathologist AUS rates ranged from 7% to 44% (mean, 19%; 926 of 4801 cases). Average AUS:M and ROM rates were 7.0% and 68% (range, 3%-35% and 25%-87%), respectively. Regression analysis highlighted pathologists' metrics that were outliers. Evaluation of the distribution of individual pathologist's TBS diagnostic categories identified patterns/trends that explained deviations from laboratory averages, including patterns of significant overcalling of benign as AUS and downgrading diagnoses across multiple TBS categories. CONCLUSIONS: Correlation of AUS, AUS:M, and ROM with molecular results, in addition to the distribution of pathologist TBS categories, offer a robust framework for quality assurance that illustrates deviations from target benchmarks, including shifts in interpretations from one TBS category to another. Giving feedback to pathologists regarding their practice patterns can help standardize diagnostic thresholds and meet designated target metrics.