Comparison of the collection approaches of 2 large thyroid fine-needle aspiration practices reveals differing advantages for cytology and molecular testing adequacy rates

Abstract

At our institution, almost all thyroid fine-needle aspiration (FNA) procedures are performed by either Endocrinology or Radiology personnel. In this study, we compared the cytology and molecular adequacy rates of these 2 thyroid FNA practices, which differ on several aspects of specimen procurement. All thyroid FNA specimens from Endocrinology and Radiology practices between September 2008 and December 2016 were included. Over this time frame, the molecular testing modality transitioned from polymerase chain reaction (PCR)-based (7-gene panel era) to next generation sequencing (NGS)-based (ThyroSeq era). In measuring cytology adequacy, the Bethesda System unsatisfactory rate was determined. Molecular adequacy was categorized as Optimal, Limited Thyroid Epithelial Cells, Limited Nucleic Acids, or Failed. These parameters were compared for the 2 practices. The study cohorts comprised 5810 specimens from Endocrinology and 4597 from Radiology. More Endocrinology specimens were satisfactory for cytology diagnosis than those from Radiology (94.7% versus 90.0%, P < 0.001). For molecular adequacy, fewer Endocrinology specimens were optimal than specimens from Radiology for both the 7-gene panel era (76.2% versus 82.9%, P < 0.001) and the ThyroSeq era (88.1% versus 91.9%, P = 0.049). The 2 thyroid FNA practices varied inversely in their adequacy rates for cytology and molecular testing. Had one practice been superior for both cytology and molecular adequacy, a recommendation for the method of choice would have been straightforward. However, our results show that optimization of FNA practice for the current practice of thyroid cytology requires further investigation due to the complex nature of specimen procurement.