Introduction: Evaluation of the differential value of the first thyroglobulin (Tg) concentration, measured after thyroidectomy (Tx) but before thyroid remnant ablation, in patients with differentiated thyroid carcinoma (DTC) as a marker of either metastases or residual cancer (M).
Material and methods: Data from 517 patients with DTC after Tx, with follow-up > 1.5 year were analysed retrospectively. Patients in whom either the course of the disease was unclear or interference in the Tg test was possible (a-TgAb [+], Tg recovery < 80%) were excluded from the study. Finally, the data from 247 patients were evaluated (age: 14-79 years; 223 women, 24 men). The results of TSH, thyroid radioiodine uptake (T(up24)), thyroid remnant volume (V) and Tg in patients with diagnosed M (group M1; n = 35) were compared with the same parameters in patients with remission > 1.5 year (group M0; n = 212). The area under the ROC curve was calculated. The clinical decision limit of Tg level to be suggestive of metastases was determined by means of efficiency curve.
Results: Groups M0 and M1 did not differ from each other with respect to TSH concentration (median 49.7 mIU/l vs 44.3; p = 0.16) or thyroid remnant volume (1.4 vs 1.1 ml; p = 0.79). However, they did differ with respect to T(up24) (7.6 vs 3.2%; p = 0.01) and Tg (4.5 vs 96.7 ng/ml; p = 0.000000). Area under ROC for Tg was 0.78 +/- 0.05 (mean +/- s.e.m.). The decision limit of Tg for suspected M was determined at 38.1 ng/ml, Tg sensitivity was 0.57 (95%CI 0.39-0.74) and specificity 0.96 (95%CI 0.92-0.98).
Conclusions: First thyroglobulin concentration, determined after thyroidectomy but before other treatment, is higher in patients with metastatic DTC than in patients without such metastases. This indicates that Tg level may be used as an early marker of either residual or metastatic DTC (even if thyroid remnants are present).