Abstract
Recently, two different ultrasensitive serum Tg assays with low functional sensitivity (FS) (0.11 ng/ml Tg Access and 0.02 ng/ml Tg e-Iason) became commercially available. Aim of this retrospective study was to evaluate whether the use of these assays in the follow-up of DTC patients during suppressive LT4 therapy, might have the same or better diagnostic accuracy compared to the traditional Tg assay.
Methods: We studied 215 DTC patients who underwent routine follow-up of DTC including rhTSH-Tg stimulation test (Tg Immulite, FS of 0.9 ng/ml) and neck ultrasound. All patients had an undetectable basal Tg and negative TgAb. According to the results of the test 173/215 (80%) met the criteria of complete remission and 42/215 (20%) had some evidence of persistent disease.
Results: Using ultrasensitive assays the diagnostic accuracy of basal Tg in detecting patients in complete remission or patients with persistent disease is reported in the table.
Conclusions: Using basal Tg with a FS of 0.13 ng/ml without performing rhTSH-Tg stimulation carried a 11.0% of false positive and 26.1% of false negative results. Using basal Tg with a FS of 0.04 ng/ml there were 2.4% of false negative and 67.7% of false positive results. Based on these results we believe that the use of ultrasensitive assays will expose too many patients probably free of disease to an intensive follow-up and thus at this moment has not advantage over the traditional follow-up strategy based on the combination of rhTSH-Tg stimulation test and neck ultrasound.