- Last Update On : 2013-02-02
Thyroglobulin (Tg) is a large glycoprotein that is synthesized in thyroid follicles and serves as the precursor of thyroid hormone (T4). Measurement of serum Tg is primarily used to detect recurrence of follicular thyroid cancer.
A preoperative serum Tg level has no diagnostic or prognostic significance by itself, but does document that Tg can be followed postoperatively as a tumor marker for that patient. Preoperative specimens should either be drawn before fine needle aspirate (FNA)or more than 3 weeks following FNA. The sensitivity of postoperative serum Tg is highest when the tumor is relatively small (2 cm or less) and the preoperative serum Tg value is high. If the preoperative Tg level is within normal limits, an undetectable postoperative Tg value is less reassuring, because it is unclear whether the tumor originallysecreted Tg.
Following thyroid sur  gery, serum Tg concentrations fall rapidly with a half-life of 2 to 4 days.Any Tg released from surgi