Ultrasensitive serum thyroglobulin measurement is useful for the follow-up of patients treated with total thyroidectomy without radioactive iodine ablation

Context: Thyroglobulin (Tg) measurement is a major tool for the follow-up of differentiated thyroid cancer (DTC) patients; however, in patients who do not undergo radioactive iodine (RAI) ablation, normal ultrasensitive Tg levels measured under levothyroxine treatment (usTg/L-T₄) are not well defined. Objective and design: This single-center retrospective study assessed usTg/L-T₄ level in 86 consecutive patients treated with total thyroidectomy without RAI ablation for low-risk DTC (nZ77) or for tumors of uncertain malignant potential (TUMP) (nZ9). Results: DTCs were classified as pT1, pT2, and pT3 in 75, 1, and 1 case respectively and pN0, pN1, and pNx in 40, 6, and 31 respectively. Following surgery, ten patients had Tg antibodies (TgAb).Among those without TgAb, the first usTg/L-T₄ determination obtained at a mean time of 9 months after surgery was ≤0.1 ng/ml in 62% of cases,≤0.3 ng/ml in 82% of cases, ≤1 ng/ml in 91%, and<2 ng/ml in 96% of cases. After a median follow-up of 2.5 years (range: 0.6-7.2 years), one patient had persistent disease with an usTg/L-T₄ at 11 ng/ml and an abnormal neck ultrasonography (US) and two patients had usTg/L-T₄ level > 2 ng/ml (3.9 and 4.9 ng/ml) with a normal neck US.Within the first 2 years following total thyroidectomy without RAI ablation, usTg/L-T₄ level is ≤2 ng/ml in 96% of the cases. Conclusion: After total thyroidectomy, sensitive serumTg/L-T₄ level is ≤2 ng/ml in most patients and can be used for patient follow-up.