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

Abstract

ContextThyroglobulin (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 designThis single-center retrospective study assessed usTg/l-T4 level in 86 consecutive patients treated with total thyroidectomy without RAI ablation for low-risk DTC (n=77) or for tumors of uncertain malignant potential (TUMP) (n=9).ResultsDTCs 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.ConclusionAfter total thyroidectomy, sensitive serum Tg/l-T4 level is ≤2 ng/ml in most patients and can be used for patient follow-up.