Calcitonin measurement on fine needle washouts: Preanalytical Issues and Normal Reference Values

Calcitonin (CT) measurement on fine‐needle aspiration cytology (FNAC) washouts (FNAC‐CT) is a promising tool in the diagnosis of medullary thyroid carcinoma (MTC). Guidelines for the method with codified cut‐off are needed to use this technique in clinical routine. This study was undertaken to assess the best pre‐analytical procedure and to define a reliable reference value for FNAC‐CT. Fifty‐four patients underwent thyroid surgery, so MTC was excluded by surgical pathology examination and CT immunostains. Before surgery, FNAC‐CT was measured on 78 thyroid nodules from such 54 patients. Needles were rinsed by normal saline and specific CT‐free dilution buffer, and CT was measured by a fully automated immunochemiluminometric assay. FNAC‐CT levels were not significantly different in normal saline or specific buffer. The calculated 97.5th upper FNAC‐CT value was 8.5 pg/mL (saline) and 7.43 pg/mL (buffer), respectively. Seeing its relatively large sample size, rigorous selection criteria and inclusion of CT immunostaining of thyroid nodules, the present study provides a reliable guideline and a clinically relevant reference value for FNAC‐CT measurement in thyroid nodules. Diagn. Cytopathol. 2013. © 2011 Wiley Periodicals, Inc.