Immediate change of serum thyroglobulin level after radioiodine treatment can be an early predictor for therapy response

Objectives The purpose of this study is to evaluate whether immediate change of serum thyroglobulin (Tg) level after radioiodine therapy can be a predictive factor for ablation of residual thyroid or metastatic lesion.

Methods 29 patients performed radioiodine therapy, and measured serum Tg level immediately (post 4 days) after (RAI) therapy and following treatment (after 6-12 months). Thyroid function test parameters, Tg and TgAb were measured by radioimmunoassay kits. rTg (Immediate Tg/1st time stimulation Tg), dTg (Immediate Tg - 1st time stimulation Tg), rTgAb (Immediate TgAb/1st time stimulation TgAb) and dTgAb (Immediate TgAb - 1st time stimulation TgAb) were calculated. I-131 whole body scan parameters were rUptake (1-(2nd time therapy uptake ratio/1st time therapy uptake ratio)) and dUptake (1st time therapy uptake ratio - 2nd time therapy uptake ratio). Uptake (Lesion ROI uptake/Brain ROI uptake) was calculated according to geometric average of lesion in anterior and posterior images of I-131 whole body scan.

Results Positive correlation between rTg and rUptake was checked by Pearson’s correlation (correlation coefficient = 0.382, P=0.041). In subgroup analysis, rTg more than 1.5 reveals significantly high rUptake and dUptake (rUptake: 0.74±0.25 vs. 0.45±0.31, P=0.01). Moreover, rUptake more than 0.7 revealed high rTg with significance (rTg: 8.80±9.50 vs. 1.31±0.81, P=0.003).

Conclusions High ratio between immediate Tg and 1st time stimulation Tg reflects high ablation rate of residual or metastatic lesion after radioiodine therapy