Any detectable thyroglobulin in lymph node biopsy washouts suggests local recurrence in differentiated thyroid cancer

The sensitivity of local recurrence detection in differentiated thyroid cancer (DTC) is increased by measuring thyroglobulin in needle washouts from lymph node fine-needle aspiration biopsies (FNA-Tg). Recent studies have proposed minimum diagnostic threshold values for FNA-Tg and have reported interference from Tg antibodies (Tg Ab), leading to low or false-negative results. The aim of this study was to assess the utility of FNA-Tg in the diagnosis of local DTC recurrence in patients referred to a single pathology service used by our tertiary teaching hospital, the first such study in an Australian cohort. Data were collected from the pathology service database for FNA-Tg over an 18-month period, and the results of 69 FNA-Tg samples from 57 patients were obtained. FNA-Tg findings were compared with cytology and histology when patients proceeded to surgery. Using the functional sensitivity as the cut-off, detectable FNA-Tg (≥0.9 μg/l) had a sensitivity of 95.7%, specificity of 50% and positive predictive value of 95.7%. Our results suggest that detectable FNA-Tg leads to histological confirmation of local nodal DTC recurrence and would support a decision to proceed to surgery. Serum Tg Ab can, however, interfere with FNA-Tg measurements. Thus, we now recommend routine use of FNA-Tg washouts in all lymph node FNA biopsies for the detection of DTC recurrence.