What is THYROGLOBULIN (TG) LEVEL?

Also Known As: Tg, TGB

Formal Name: Thyroglobulin, Serum or Plasma

Thyroglobulin (Tg) is a protein produced uniquely by your thyroid gland. This test measures the amount of thyroglobulin in the blood.
The thyroid gland produces hormones (thyroxine or T4 and triiodothyronine or T3) that help to regulate the rate at which the body uses energy. It is a small, butterfly-shaped organ that lies flat against the windpipe at the base of the throat and is composed primarily of very small, ball-shaped structures called follicles that produce and store thyroglobulin.

Thyroglobulin serves as the source of T4 and T3. The production of these hormones and their release into the bloodstream are stimulated by the pituitary hormone TSH (thyroid-stimulating hormone).

Thyroglobulin is produced in all healthy individuals, and normally its level in blood is low. Thyroglobulin levels increase in both benign (Graves disease, subacute thyroiditis, Hashimoto thyroiditis) and thyroid cancer. Therefore, it is on one hand a non-specific indicator of thyroid dysfunction and, on the other hand, a tumor marker that can be used to monitor patients with thyroid papillary and follicular cancer after diagnosis (see the Thyroid Cancer article).

How is the test used?

The thyroglobulin test is primarily used as a tumor marker to evaluate the effectiveness of treatment for thyroid cancer and to monitor for recurrence. Not every thyroid cancer will produce thyroglobulin, but the most common types, the well-differentiated papillary and follicular thyroid cancers, frequently do, resulting in increased levels of thyroglobulin in the blood.

Thyroglobulin testing may be used, along with a TSH test, prior to thyroid cancer treatment to determine whether the cancer is producing thyroglobulin. If it is, then the test can be ordered at intervals after treatment to monitor for cancer recurrence. Several thyroglobulin levels may be ordered over a period of time (serial samples) to look at the change in levels. The change or pattern of results often provides more information than a single value.

Thyroglobulin testing is also occasionally ordered to help determine the cause of hyperthyroidism and to monitor the effectiveness of treatment for conditions such as Graves disease.

Rarely, the test may be ordered to help differentiate between subacute thyroiditis and thyrotoxicosis factitia (hyperthyroidism caused by ingesting excess thyroid hormone pills) and to determine the cause of congenital hypothyroidism in newborns.