Serial stimulated thyroglobulin measurements are more specific for detecting distant metastatic differentiated thyroid cancer before radioiodine therapy

OBJECTIVE: Preablative stimulated thyroglobulin (ps-Tg) has the potential to be used in identifying distant metastatic differentiated thyroid carcinoma (DM-DTC), but its single level can be affected by remnant thyroid tissue and thyrotropin (TSH). The objective of this retrospective study was to evaluate the value of serial ps-Tg measurements in identifying DM-DTC specifically. METHODS: A total of 317 DTC patients with serial measurements of ps-Tg, TSH and anti-Tg antibody were divided into M1 (n=72) and M0 (n=245) according to the presence of distant metastasis (DM) or not. The initial ps-Tg measurement, with a corresponding TSH exceeding 30 μIU/mL, was marked as Tg1, and ps-Tg measured right before radioactive iodine (RAI) therapy was defined as Tg2, with a median interval of 8 days. ΔTg denotes Tg2–Tg1, and ΔTSH denotes TSH2–TSH1. Tg1, Tg2, ΔTg, and ΔTg/ΔTSH were tested for efficacy in identifying DM-DTC using receiver operating characteristic (ROC) curve analysis, and further compared with chest computed tomography (CT) and posttreatment whole-body RAI scan (RxWBS). RESULTS: Compared with single ps-Tg measurement (Tg1 or Tg2), both ΔTg and ΔTg/ΔTSH were more narrowly distributed around zero in the M0 group, which made their distribution in the M1 group more distinguished in a relatively dispersed way. ΔTg/ΔTSH manifested a higher accuracy (88.64%) and specificity (90.20%) in identifying DM-DTC than Tg1 or Tg2 measurements, with a much higher specificity than chest CT (90.20% vs. 66.00%) and a much higher sensitivity than RxWBS (83.33% vs. 61.11%). CONCLUSIONS: Serial ps-Tg measurements even over as short an interval as 8 days hold incremental value in identifying DM-DTC. ΔTg/ΔTSH is a specific early biochemical marker for DM-DTC.