Value of serial preablative thyroglobulin measurements: can we address the impact of thyroid remnants?

Preablative stimulated thyroglobulin (ps-Tg) is somewhat nonspecific when used as a predictive marker for distant metastases (DM) from differentiated thyroid carcinoma because of the impact of residual tissue postsurgery. The aim of this study was to explore the potential value of serial ps-Tg measurements and assess the clinical value of these measurements in the context of thyroid remnants.

A total of 370 consecutive differentiated thyroid carcinoma patients with serial measurements of ps-Tg, thyrotropin (TSH), and anti-Tg antibody before radioactive iodine ablation were included in the study. Patients were divided into those with DM (n=76) and non-DM with no remnant thyroid (NRT, n=53), moderate remnant thyroid (MRT, n=206), and overt remnant thyroid (ORT, n=35) on the basis of uptake in the thyroid bed on the whole-body I scan. The initial ps-Tg and the last one collected immediately before radioactive iodine ablation were marked as Tg1 and Tg2, respectively, with a median interval of 8 days. The change was marked as ΔTg. The same was applied for serum TSH values. Both single parameters (Tg1, Tg2) and ΔTg were compared among different groups. The velocity of ps-Tg change as well as ΔTg/ΔTSH was also used to alleviate the impact of time and TSH levels on ps-Tg.

Patients with ORT presented with significantly higher single ps-Tg values than those with MRT and NRT (both P<0.01), with the highest initial Tg value of 194.4 ng/ml, which was higher than most patients with DM (median: 104.3 ng/ml). However, no differences were observed among ORT, MRT, and NRT when ΔTg, velocity of ps-Tg change, or ΔTg/ΔTSH was used as an index (both P>0.05), which implies that the change parameters can be used as predictors of DM involvement even in the context of significant residual thyroid tissue.

In comparison with a single ps-Tg measurement, changes in ps-Tg values even over as short an interval as 8 days can provide clinical guidance for possible metastatic involvement even in the context of significant thyroid remnant tissue.