The Diagnostic Value of Calcitonin Measurement in Wash-out Fluid from Fine-Needle Aspiration of Thyroid Nodules in the Diagnosis of Medullary Thyroid Cancer

Objective The diagnostic value of calcitonin measurement in fine-needle aspiration biopsy (FNAB) washout fluid (Ct-FNAB) for medullary thyroid cancer (MTC) remains to be determined. This prospective study aimed to assess the diagnostic value of Ct-FNAB in thyroid nodules in comparison with basal serum calcitonin (Ct), pentagas- trin-stimulated Ct (Pg-sCt), and cytology. Methods Among patients with goiter addressed with US-FNAB who had an initial clinical suggestion for thyroidectomy, 27 patients with thyroid nodule/s (n = 60) and normal, borderline, or increased Ct fulfilled the criteria for thyroidectomy. All 27 patients (enrolled according to exclusion/inclusion criteria) underwent ultrasonography (US), Ct, Pg-sCt, US-assisted FNAB of each patient’s nodule for both cytology, and Ct-FNAB before thyroidectomy. Results Ct-FNAB always resulted in >1,000 pg/mL in MTC nodules at histology. For values between 36 and pg/mL, MTCs and nodular or micronodular C-cell hyperplasia (CCH) results overlapped. Most of the nodules without MTC and/or CCH had Ct-FNAB <17 pg/mL. Ct-FNAB diagnostic power was superior to and similar to other diagnostic procedures (Ct, Pg-sCt, and cytology) in identifying both MTC and CCH, and MTC alone, respectively. Conclusion The diagnostic power of Ct-FNAB is valuable compared with other routine procedures. Ct-FNAB is highly reliable for the early detection and accurate localization of MTC in thyroid nodules, but it does not differentiate between MTC and CCH. Ct-FNAB is an extremely valuable diagnostic tool, especially considering that other diagnostic procedures do not provide a definitive diagnosis, and it can be included in the clinical work-up of thyroid nodules when MTC is suspected. (Endocr Pract. 2013;19:769-779)