Cut-off value for needle washout thyroglobulin in athyrotropic patients

Objectives/Hypothesis: The purpose of this study was to determine the appropriate cut-off value for fine needle aspiration-thyroglobulin (FNA-Tg) associated with postoperative recurrences and validate the diagnostic efficacy of FNA-Tg in patients after total thyroidectomy compared with concomitant cytology (C). Study Design: Retrospective. Methods: We retrospectively evaluated the results of ultrasound-guided FNAs performed for suspicious cervical lesions of 40 patients (male:female = 10:30; mean age, 44.0 years) after total thyroidectomy (mean duration, 89.1 months), to acquire the material for Tg and C analysis. After collection of the cytologic sample, we rinsed the same needle with 1 mL of normal saline for Tg radioimmunoassay. Results: Of 40 lesions (mean size, 0.89 cm; range, 0.3-3.5cm), 21 were confirmed as recurrences and 19 were nonrecurrences. The rates of nondiagnostic sampling and sensitivity and specificity of FNA-C when diagnostic sampling was obtained were 40% (16/40), 100% (14/14), and 90.0% (9/10), respectively. According to receiver operating characteristic analysis, the optimal cut-off value of FNA-Tg was 4.1 ng/mL (sensitivity, 100% [21/21]; specificity, 100% [19/19], P < .05). Furthermore, in 16 inconclusive lesions due to nondiagnostic cytologic results, the FNA-Tg results coincided with a final diagnosis (seven recurrences and nine nonrecurrences). The cases with maximum diameters <1 cm showed a significantly increased rate of nondiagnostic cytologic results, and the FNA-Tg results were more helpful than lesions ≥1 cm in diagnosing a recurrence (P < .05). Conclusions: Measurement of FNA-Tg is helpful for distinguishing recurrent from nonrecurrent lesions in the majority of patients who were previously treated for well-differentiated papillary thyroid carcinoma.