Tyroglobulin

Tyroglobulin is generally considered a misspelling of thyroglobulin, the thyroid follicular cell–secreted glycoprotein that serves as the precursor to thyroid hormones T3 and T4.

Thyroglobulin is synthesized in thyroid follicular cells and released into the colloid of the thyroid follicle, where iodination and coupling of tyrosine residues occur via thyroid peroxidase to form T3 and T4 while still attached to the protein.

The thyroglobulin molecule is large and heavily glycosylated, with an approximate molecular weight of 660 kDa. It is encoded by the TG gene in humans and stored in the colloid as the substrate for hormone synthesis.

When stimulated by thyroid-stimulating hormone (TSH), thyroglobulin is endocytosed by follicular cells, proteolyzed in lysosomes, and the released T3 and T4 are freed into circulation.

Clinically, serum thyroglobulin is used as a tumor marker to monitor differentiated thyroid cancer after surgery and ablation; the accuracy is affected by anti-thyroglobulin antibodies.

In pathology and research, thyroglobulin staining helps identify thyroid-origin tissues and tumors, providing a useful marker for confirming thyroid differentiation.