Endocrine Abstracts

Introduction: Undetectable concentration of Tg after rhTSH stimulation (Tg/rhTSH) is one of the most important criteria in evaluating the effectiveness of radioiodine ablation in patients with differentiated thyroid cancer (DTC) treated with 131I.

Aim: To evaluate the possibility of using L-T4 suppression treatment (Tg/L-T4) measurements by the ultrasensitive method TRACE (immunofluorescence method) with the KRYPTOR analyzer instead of the Tg/rhTSH measurements with the chemiluminescent immunoassay (CLIA).

Material: The study was performed on 34 consecutive DTC patients after surgery and adjuvant treatment with 131I, referred for evaluation of ablation effectiveness 9 months after 131I treatment.

Method: Tg measurement was performed in patients during L-T4 treatment at two time points: before administration of rhTSH and 5 days after the first injection, using both tests: Tg detection with CLIA (analytical sensitivity 0.2 ng/ml and functional sensitivity of 0.9 ng/ml) and Tg by TRACE (analytical sensitivity of 0.09 ng/ml and functional sensitivity 0.15 ng/ml).

Results: Tg/L-T4 concentration in all patients was <1.0 ng/ml in the CLIA assay, and in the range of <0.09 ng/ml – 0.354 ng/ml in the TRACE assay. After rhTSH stimulation, Tg concentration of <1.0 ng/ml (excellent treatment response) as measured by CLIA was found in 30/34 patients. In four patients, however, Tg/rhTSH was in the range of 1.0–10.0 ng/ml (1.02, 1.83, 2.2, 9.24 ng/ml – indeterminate response). In the latter group Tg/L-T4 by TRACE was 0.09 ng/ml; 0.1141 ng/ml; 0.1629 ng/ml; 0.09 ng/ml.

Conclusions: 1 None of the four cases with indeterminate response to ablation showed elevated Tg/L-T4 concentrations according to the ultrasensitive TRACE assay.

2 Results in our trial group do not entitle us to recommend determinations of Tg/L-T4 with the TRACE method instead of the Tg/rhTSH in assessing the ablation efficacy.

3 It is necessary to validate the method on a larger group of patients.