Reporting thyroid FNA before and after implementation of the Bethesda system-one institution's experience

The Bethesda System for Reporting Thyroid Cytopathology was published in 2008 and was implemented at Beth Israel Deaconess Medical Center (BIDMC) in June, 2010. Prior to this date, our diagnostic scheme was similar to the Bethesda System, except for the category of "Atypia/Follicular Lesion of Undetermined Significance" (AUS). This study evaluates the impact of the Bethesda System on the rate and the positive predictive value (PPV) of the diagnostic categories at BIDMC.

We performed a retrospective review of all thyroid fine-needle aspirations (FNAs) during the time periods January, 2006 to November, 2008 and June, 2010 to July, 2011 and the subsequent thyroidectomy specimens.

Post-Bethesda System, diagnoses that are equivocal for diverse reasons and which have wide-ranging PPVs are now all grouped into the AUS category, and the proportion of cases that are in the atypical/AUS category rose from 3.7% in the pre-Bethesda period to 12% in the post-Bethesda period.

The AUS category has a PPV approaching 50% in our lab. This creates uncertainty regarding the appropriate management for this category and may cause unnecessary overuse of molecular testing for cases in the AUS category.