Thyroglobulin (Tg)
Produced by: Thyroid gland
Definition / Purpose: Thyroglobulin (Tg) is a protein produced by the thyroid gland and used entirely within the thyroid gland.  It is a precursor to T4 and T3.
Lab Reference Range: <0.1 ng/mL (or if testing LC/MS/MS Thyroglobulin: < 0.4 ng/ML)
When to order:

• Sometimes used for the screening and monitoring of Thyroid cancer.

Pearls:
Half-life: 65 hours.
Elevated Estrogen levels will increase Tg.
The major reason to measure TG is to monitor, but not to diagnose, patients with well-differentiated thyroid cancers. The measurement of thyroglobulin, after thyroidectomy and ablation of the thyroid gland, is useful to determine metastasis.
Thyroglobulin (Tg) and Thyroglobulin Antibody (TgAb) are two different things. The former is an protein normally produced by the thyroid gland. The latter is an autoantibody produced by local white blood cells causing an abnormal autoimmune reaction that slowly destroys Thyroglobulin through an inflammatory process.