Calcitonin measurement on fine needle washouts: preanalytical issues and normal reference values

Area of Science:

• Endocrinology
• Oncology
• Cytopathology

Background:

• Calcitonin (CT) measurement in fine-needle aspiration cytology (FNAC) washouts (FNAC-CT) shows promise for diagnosing medullary thyroid carcinoma (MTC).
• Standardized guidelines and cut-off values are essential for integrating FNAC-CT into routine clinical practice.
• This study addresses the need for optimized pre-analytical methods and a validated reference value for FNAC-CT.

Purpose of the Study:

• To evaluate the optimal pre-analytical procedure for FNAC-CT measurement.
• To establish a reliable reference value for FNAC-CT in thyroid nodules.
• To facilitate the clinical adoption of FNAC-CT for MTC diagnosis.

Main Methods:

• FNAC-CT was measured in 78 thyroid nodules from 54 patients prior to surgery, with MTC excluded by pathology and CT immunostains.
• Needle rinsates were analyzed using both normal saline and a specific CT-free dilution buffer.
• Calcitonin levels were quantified using a fully automated immunochemiluminometric assay.

Main Results:

• FNAC-CT levels did not significantly differ between normal saline and the specific buffer.
• The 97.5th percentile upper FNAC-CT values were determined as 8.5 pg/mL for saline and 7.43 pg/mL for the buffer.
• These findings suggest consistency in measurement regardless of the rinsing solution used.

Conclusions:

• The study provides a reliable guideline and a clinically relevant reference value for FNAC-CT.
• The established reference values can aid in the routine diagnostic application of FNAC-CT for thyroid nodules.
• Rigorous methodology supports the clinical utility of FNAC-CT in MTC diagnosis.