Clinical relevance of highly-sensitive Tg assay in monitoring low-risk patients treated for differentiated thyroid cancer on suppressive L-Thyroxine therapy

Objective: Serum Thyroglobulin (Tg) represents a high specific biomarker for the detection of residual functioning thyroid tissue and/or recurrence/metastases in the follow-up of treated patients for differentiated thyroid cancer (DTC). Recently, several highly sensitive Tg assays have been developed but their clinical benefit still remains undetermined. Design: We evaluated the clinical impact of Tg values measured by a highly sensitive Tg assay (Access, Beckman) during L-Thyroxine (L-T4) suppressive therapy in a group of 106 low-risk DTC-treated patients, submitted to routinely follow-up including Recombinant Human Thyrotropin stimulation (rh-TSH). Main Outcome: Undetectable (i.e. 0.1 mg/L) Tg Access showed a very high negative predictive value (99%) of a Tg negative response (i.e. 2 mg/L) to rh-TSH. Minimal amounts of measurable Tg, (i.e. 0.1 but 1 mg/L) during L-T4 therapy correctly identified the majority of patients (80%) with a positive (2 mg/L) response to rh-TSH. Conclusions: Our results indicate that routinely introduction of a highly-sensitive Tg assay may represent a useful diagnostic tool which helps to better interpret Tg results during monitoring of DTC-treated low-risk patients on L-T4 suppressive therapy and to optimize the execution of the more expensive rh-TSH test.