Thyroglobulin and Antibodies

Thyroglobulin (Tg) is produced by the thyroid gland as the precursor to thyroid hormone (see Chapter 52). 

The main use of Tg measurement is as a tumor marker for patients with a diagnosis of differentiated thyroid cancer. Approximately two thirds of these patients have an elevated preoperative Tg level. An elevated preoperative level of Tg confirms the tumor s ability to secrete Tg and validates the use of postoperative measurement of Tg to monitor for tumor recurrence. Postoperatively, the most sensitive method to detect residual tumor or metastasis is after TSH stimulation. In weU-differentiated tumors, a tenfold increase in Tg levels is seen after TSH stimulation. Poorly differentiated tumors, that do not concentrate iodide, may display a blunted response to TSH stimulation. 

Antithyroglobulin antibodies can also be used to monitor residual disease and/or recurrence. Serial anti-Tg measurements may be an independent prognostic indicator of therapy, because an increase in anti-Tg antibodies may suggest recurrence of the tumor.  

IMA and RIA are the two main methods used for the measurement of Tg. The IMA assays have the advantage of having a shorter incubation time and are automatable however, they suffer from greater interferences. The main interferants in both assays are antithyroglobulin antibodies, which cause an underestimation of Tg levels in the IMA. Antithyroglobulin antibodies can either be measured directly in all patients or if both IMA and RIA are used to measure Tg, a discordant result suggests the presence of anti-thyroglobulin antibodies. 

Chromogranins are a family of proteins that are major components of the secretory granules of most neuroendocrine cells. 

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