Thyroglobulin

TG (thyroglobulin)

Thyroglobulin (TG) is a dimeric glycoprotein, serving as template for the synthesis of thyroid hormones. It is the most important component of thyroid protein being synthesized in large quantities by thyrocytes and stored in the follicular lumen.

Thyroid hormone biosynthesis is done in four steps:

1) uptake and concentration of iodides in the thyroid;

2) oxidation of the iodides with the formation of elemental iodine;

3) incorporation of molecular iodine in thyroglobulin with rapid formation of 3-monoiodothyrosine (MIT) and 3,5-diiodothyrosine (DIT); by condensation of a MIT radical and a DIT radical T3 is formed and the condensation of the two DIT radical T4 is formed ;

4) proteolysis of thyroglobulin – the final stage, stimulated TSH release of hormones circulating T3 and T4

During synthesis of thyroglobulin in thyrocytes and transport to the thyroid follicles there will be small amounts of protein released  in circulation. Thus in the serum of healthy individuals there are detected low concentrations of thyroglobulin, indicating the presence of thyroid tissue.

On the other hand, damage to the follicle wall in the bloodstream accompanies the release of a large amount of thyroglobulin; the protein therefore is a morphological marker of the integrity of the thyroid gland.

Elevated thyroglobulin shows three types of thyroid disease: goiter with thyroid hyperfunction, or traumatic inflammation of the thyroid and differentiated thyroid cancer.

The absence of serum thyroglobulin newborn congenital indicates athyreosis.

Indications for thyroglobulin determination:

• monitoring of patients with differentiated thyroid cancer after total thyroidectomy and radioactive iodine treatment.

In patients with thyroid cancer without surgery or irradiation or with left-over thyroid tissue, thyroglobulin levels should be undetectable. Thus thyroglobulin is a useful tumor marker in evaluating this residual thyroid papillary-follicular carcinoma, after surgical resection and / or radiation.

If during the monitoring period and suppressive therapy with thyroxine thyroglobulin values> 3 mg / L are obtained, these are an indicator of tumor recurrence and total corporeal scintigraphy is recommended to be performed with iodine131.

• destructive thyroiditis;

• Differential diagnosis between sub-acute thyroiditis and artificial thyrotoxicosis (caused) – in artificial thyrotoxicosis thyroglobulin values ​​are very low or undetectable.

• congenital hypothyroidism to distinguish between complete absence of the thyroid gland and thyroid hypoplasia or other pathological conditions.

Method – Elisa.

Normal values ​​<40 ng / mL;