Thyroglobulin

General Information

Thyroglobulin (Tg) is a large glycoprotein (~660 kDa) produced in response to TSH, by thyroid follicular cells and stored in the follicular colloid of the thyroid gland. It is the precursor for the synthesis of thyroxine (T4) and triiodothyronine (T3) and is found in the serum as a by product of thyroid hormone synthesis and secretion.

Due to the sole source of Thyroglobulin being the thyroid gland, patients who have had thyroidectomies for the treatment of differentiated thyroid carcinoma may have their serum Thyroglobulin levels measured to monitor for recurrence of disease or metastases. Following successful removal of the thyroid gland, leaving no thyroid remnants or remaining disease the Thyroglobulin levels measured should be undetectable.

Thyroglobulin antibodies (TgAb) are auto-antibodies present in approximately 25% of patients with differentiated thyroid carcinoma (DTC) and 10% of the general population, although the reason for this is not completely understood. Thyroglobulin antibodies most commonly cause negative interference in immunometric assays but can also cause positive interference. For this reason Thyroglobulin antibodies should be measured on all samples requesting Thyroglobulin to aid interpretation, and where antibodies are raised Thyroglobulin should be analysed by an alternative method for confirmation.

For UHB patients, we currently use an Abbott Alinity immunometric assay (TgIMA) as our front line test for thyroglobulin, along with Thyroglobulin antibodies testing. For samples with positive TgAb, thyroglobulin by radioimmunoassay (TgRIA) is then automatically added on.

External users may request the full testing pathway used for internal UHB patients (TgIMA and TgAb initially, with TgRIA added if antibody positive), or they may request only the TgRIA assay. Please make it clear on the request form which assay(s) are required.

Patient Preparation

None. Thyroid function tests should be done at same time.