Proteinase K treatment improves RNA recovery from thyroid cells fixed with liquid-based cytology solution

BMC Res Notes. 2018 Nov 20;11(1):822. doi: 10.1186/s13104-018-3914-4.


Objective: Fine-needle aspiration biopsy (FNAB), an important diagnostic tool given its simplicity, safety, and cost-effectiveness, is fast becoming a popular procedure in the diagnosis of thyroid diseases. Generally, cells isolated from biopsies are transferred directly to microscope slides to prepare smears for cytopathological examination; however, the technical difficulties of this procedure often cause poor reproducibility, which limits the accuracy of diagnostic results. Liquid-based cytology (LBC), in which isolated cells are collected in a fixative solution, is advantageous in that it facilitates the preparation of homogenous cytological specimens. However, LBC has not been applied to molecular diagnoses, such as RNA expression-based diagnosis, mainly because of difficulties in cell recovery and RNA isolation. This study was aimed to improve RNA extraction from papillary cancer-derived K1 cells and thyroid FNAB specimens suspended in LBC solutions.

Results: K1 cells suspended in CytoRich-Red and CytoRich-Blue, fixatives for LBC, were efficiently recovered by trapping to glass-fiber filters. Importantly, subsequent Proteinase K treatment was essential for efficient RNA extraction from the fixed cells. This finding was also applicable to RNA extraction from CytoRich-Red-fixed thyroid FNAB specimens processed in the same way. Consistently, U6 small nuclear RNA was detected in these RNA samples by reverse transcription-polymerase chain reaction.

Keywords: Fine-needle aspiration biopsy; Liquid-based cytology; RNA; RNA integrity number; Thyroid cancer.

MeSH terms

  • Biopsy, Fine-Needle / methods*
  • Cost-Benefit Analysis
  • Cytodiagnosis
  • Cytological Techniques / methods*
  • Endopeptidase K / chemistry*
  • Humans
  • RNA / isolation & purification*
  • Reproducibility of Results
  • Thyroid Gland / cytology
  • Thyroid Neoplasms / genetics*


  • RNA
  • Endopeptidase K