Endocrine Abstracts

Introduction: Guidelines suggest that serum basal (nonstimulated) thyroblobulin (bTg) with sensitive assays (Functional Sensitivity-FS- below 0.1 or 0.2 ng/ml) could substitute the measurement of serum Tg levels after TSH stimulation during the follow-up of patients with differentiated thyroid cancer (DTC) when basal results fall below the FS.

Objective: A sensitive assay for Tg was incorporate in our center (Chemiluminiscent Tg Access; Beckam Coulter; Brea; CA) with FS of 0.1 ng/ml coexisting with an older traditional assay (Inmunoradiometric SelcoTg assay; Berlin) with higher FS (0.5 ng/ml). The aim of this study was to verify that sensitive bTg values below FS could obviate the need of stimulation with recombinant (rTSH) in patients consecutively seen for the follow-up of CDT in one endocrinology office between January and June 2017.

Patients and methods: Patients with DTC from one endocrinology office were included if:

– They underwent total thyroidectomy usually followed by 131 iodide ablation.

– They had a recent documented bTg determined with the sensitive assay (provided that Tg antibodies were negative) and a recent stimulated Tg (sTg) after rTSH administration determined with the IRMA assay.

Patients were classified in 3 categories:

– Excellent treatment responders: no clinical, biochemical or structural evidence of disease and sTg (IRMA method) below 1 ng/ml.

– Patients with structural disease cytologically or hystologically evidentiated.

– Incomplete biochemical responders: sTg above 1 ng/ml (IRMA method) in the absence of localizable disease.

Results: Study included 26 patients (4 men), mean age (DS): 49(15) years with DTC treated with total thyroidectomy (some of them with central and lateral neck dissection) followed by an¹³¹Iodide ablative dose in 25 cases. 4 patients had been reoperated and 3 received a second ¹³¹ Iodide dose because of recurrent nodal disease. Among Excellent treatment responders (n=21), bTg was lower than 0.1 ng/ml in all but one case (0.2 ng/ml). In the case with structural disease (metastatic nodal recurrence) bTg raised above FS level (3.4 ng/ml). Among Incomplete biochemical responders (n=4), 3 had bTg >0.1 ng/ml and that one with bTg <0.1 ng/ml had a marginally sTg (1.2 ng/dl) with the traditional assay of doubtful clinical significance.

Conclusion: Sensitive Tg methods could obviate the need for sTg in a majority of DTC patients and therefore could simplify the follow-up and alleviate the costs of rTSH.