Follow-up of patients with thyroid cancer and antithyroglobulin antibodies: a review for clinicians

Antithyroglobulin antibodies (TgAb) are present in up to 25% of patients with differentiated thyroid carcinoma on initial postoperative assessment. Detectable concentrations of TgAb even below the manufacturer's cut-off can interfere with serum thyroglobulin (Tg) determination. When Tg is quantified using an immunometric assay (IMA) (hereafter referred to as Tg-IMA), this interference results in underestimated values of Tg. Although promising, more clinical trials evaluating the capacity of liquid chromatography/tandem mass spectrometry and of new assays to detect elevated Tg in patients with TgAb and structural disease are necessary, particularly when Tg is undetectable by a second-generation IMA (Tg-(2G)IMA). Neck ultrasonography (US) should be performed in patients submitted to total thyroidectomy and with negative Tg-IMA but with detectable TgAb more than 6 months after initial therapy. In patients treated with I-131, comparison of TgAb concentrations obtained before this treatment is useful to estimate the risk of disease and to guide the investigation. If initial assessment does not reveal any persistent tumor, the repetition of US is recommended while TgAb persist. Significant elevation of TgAb requires extended investigation. On the other hand, patients with negative Tg-IMA and US without abnormalities who exhibit a reduction > 50% in TgAb generally do not require investigation. Although TgAb can interfere with Tg, the management and follow-up of patients submitted to total thyroidectomy with borderline TgAb can probably be the same as those recommended for patients without TgAb if Tg-(2G)IMA and US indicate an excellent response to therapy. Currently, the presence/absence or the trend of TgAb levels cannot be considered in the follow-up of patients submitted to lobectomy.