The reliability of TSH-stimulated thyroglobulin without considering serum TSH after thyroid hormone withdrawal

Objectives TSH-stimulated thyroglobulin (TSH-s-Tg) is the most sensitive marker for detecting persistent or recurrence of differentiated thyroid cancer (DTC). Tg produced by DTC is known to be regulated by TSH, however, TSH after each thyroid hormone withdrawal (THW) cannot be identical even in the same patient. The object of this study was to evaluate influence of TSH on TSH-s-Tg after THW.

Methods Six hundred and fifty-two patients with DTC underwent measurements of TSH and Tg at 3 and 4 weeks THW due to limited TSH elevation (<30μU/mL) at 3 weeks THW. Among the 652 patients, the patients with the TSH >30μU/mL and Tg ≥2ng/mL at 4 weeks THW were selected. Finally, 117 patients were enrolled. Paired samples t-test was used to compare the TSH and Tg between 3 and 4 weeks THW in each patient. The percentage change in TSH (delta TSH) and Tg (delta Tg) between 3 and 4 weeks THW were calculated [delta TSH (or Tg) = {TSH (or Tg) at 4 weeks THW - TSH (or Tg) at 3 weeks THW} / TSH (or Tg) at 3 weeks THW x 100], and correlation analysis (Pearson's correlation coefficient) was performed to determine whether the delta TSH could affect delta Tg. TSH-s-Tg cut-off for diagnostic imaging was 2ng/mL in the study.

Results TSH and Tg at 4 weeks THW were significantly higher than those at 3 weeks THW (TSH; 56.2 vs. 16.3, p< 0.0001, Tg; 31.4 vs. 12.1, p<0.0001). Delta TSH was ranged from 42.0% to 7827.5% (mean, 480.4% [SD, 874.6%]), and delta Tg was ranged from 10.3% to 4066.7% (mean, 442.6% [SD, 572.1%]). Delta TSH was significantly correlated with delta Tg (r=0.3957; p<0.0001). Forty-eight percent of patients had a Tg <2ng/mL at 3 weeks THW, however, all of those patients had a final stimulated Tg ≥2ng/mL.

Conclusions TSH was quite diverse by period of THW among each patient. The TSH-s-Tg was significantly increased according to the percentage change in the TSH. Therefore, careful consideration should be given to the level of TSH when interpret meaning of TSH-s-Tg in DTC patients.