Stability of DNA, RNA, cytomorphology, and immunoantigenicity in residual thinprep^® specimens

The aim of this study was to evaluate the quality of residual liquid-based preparation (LBP) sample after cytopathologic diagnosis. Cervical swab, body fluid, and thyroid fine-needle aspiration (FNA) samples preserved in ThinPrep PreservCyt^® solution were tested. Samples kept frozen at -80 °C and stored at room temperature were tested 12 months after the initial sample collection. Gel electrophotography of GAPDH multiplex PCR, RNA integrity number (RIN) values obtained from Agilent bioanalyzer, cytomorphologic changes, and immunohistochemical staining (cytokeratin, thyroid transcription factor-1 (TTF-1), and D2-40) were used for the evaluation of sample quality. All available samples showed successful amplification products in multiplex PCR. However, RNAs in all residual samples were degraded with low RIN values (RIN < 4). RIN values decreased rapidly when samples were stored at room temperature in LBP medium. Cytomorpholoic evaluation and immunohistochemical staining results revealed no change regardless of storage time or storage temperature. In conclusion, RNAs stored in LBP medium degraded quickly at room temperature. Residual alcohol-based LBP cytologic specimens stored at -80 °C and room temperature showed no change in DNA quality, cytomorphology, and immunoreactivity during at least one year of storage.