Evaluation of the diagnostic value of the first thyroglobulin determination in detecting metastases after differentiated thyroid carcinoma surgery.

AIM: Evaluation of the diagnostic value of the first thyroglobulin (Tg) level measurement, performed after thyroidectomy, before another treatment, as an early marker of either metastases or local recurrence of differentiated thyroid carcinoma (DTC). MATERIALS AND METHODS: Data of 178 patients (160 women, 18 men, 14-79 years) with DTC and without known interference in Tg assay were evaluated retrospectively. In all patients, neck radioiodine uptake (Tup (24)), thyroid remnants volume (V), TSH and Tg were measured. The Tg/V and Tg/Tup (24) ratios were calculated to correct Tg concentration with regard to V and Tup (24). Six months after initial evaluation and routine therapy all patients underwent control examinations under endogenous TSH stimulation. RESULTS: During follow-up metastases or local recurrence were found in 32 patients. The groups of patients with no diagnosed metastases (M0) and with detected metastases (M1), did not differ with regard to V, serum TSH or Tup (24); difference between the two groups was found in Tg concentration (4.3 ng/ml VS 97.4 ng/ml; p=0.000001). The ratios of Tg/Tup (24) (p=0.000000) and Tg/V (p=0.004) were lower in the group M0 than M1. The areas under receiver operating characteristic curves (ROC) for Tg concentrations, Tg/Tup (24), and Tg/V ratios were 0.773 (95% CI - 0.655-0.892), 0.817 (0.709-0.925) and 0.712 (0.541-0.884), respectively. CONCLUSIONS: Both the absolute Tg concentration and Tg/V and Tg/Tup (24) ratios, determined after thyroidectomy but before another treatment in patients with metastases of DTC, diagnosed within 6 months after (131)I administration, are higher than those in patients without such metastases. This indicates that the mentioned parameters may be applied as early markers of either local recurrence or metastases of DTC. The highest discriminative value demonstrates Tg/Tup (24) ratio, Tg concentration has a lower value and Tg/V ratio has the lowest one.