Thyroglobulin measurement on fine-needle washout fluids: Influence of sample collection methods

Thyroglobulin (Tg) measurement on fine-needle aspiration (FNA) specimens (Tg-FNA) is useful in the management of patients affected by differentiated thyroid carcinoma. However, the preanalytical procedure for FNA-Tg measurement is not standardized. We evaluated the accuracy of FNA-Tg measurement by using different tubes for needle washout fluids collection.Ultrasound-guided FNA was performed on a combined 156 lesions from 108 patients. Following cytology sampling, the needles were rinsed by normal saline and aliquots collected into three different tubes (plain serum tube, serum separator tube, and lithium-heparin tube, respectively). The Tg-FNA was measured by an immunoradiometric assay.The cytological examination was nondiagnostic in six cases, false-positive in one, and false-negative in two cases. The Tg-FNA was higher in plain serum tubes as compared with serum separator and lithium-heparin ones. FNA-Tg measurement on plain serum and serum separator tubes showed a 100% sensitivity while two false-negative results occurred by lithium-heparin tubes (sensitivity 98%).The diagnostic performance of FNA-Tg compared favorably with cytology. However, biases in FNA-Tg measurement may be introduced by different collection tubes. A collection of standardized washout fluids volume into plain serum tubes is highly recommended. Serum separator tubes and lithium-heparin tubes may lower measured FNA-Tg concentration.