Thyroglobulin
A protein made only by thyroid cells - used mainly as a surveillance marker after thyroid cancer treatment.
Thyroglobulin (Tg) is a large protein produced exclusively by thyroid follicular cells - the main cell type in the thyroid gland. It serves as the precursor from which T4 and T3 are made and stored within the thyroid follicles.
In healthy people, small amounts of thyroglobulin are detectable in the blood. Its main clinical use is as a tumour marker after total thyroidectomy for thyroid cancer. Once the thyroid has been surgically removed and any residual tissue ablated with radioactive iodine, thyroglobulin levels should fall to very low or undetectable values. A rising thyroglobulin during follow-up may indicate recurrent or residual thyroid tissue, prompting further investigation.
Thyroglobulin measurement can be interfered with by thyroglobulin antibodies (anti-Tg), which are therefore measured alongside it in cancer follow-up blood tests.
Thyroglobulin is not a first-line test for diagnosing general thyroid conditions - it is specifically relevant to thyroid cancer surveillance.
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