Thyroglobulin (Tg) is a glycoprotein of 660 kDa localized within the colloid of the thyroid follicle where it is synthesized under the influence of thyrotropin. It plays an essential role in the storage of iodine and acts as precursor for the synthesis of thyroid hormones T3 and T4. Elevated thyroglobulin serum concentrations have been reported in various thyroid diseases, such as hyperthyroidism, non-toxic goitre, thyroiditis and differentiated thyroid carcinoma.
The main clinical application for the Tg determination, however, is represented by the post-operative monitoring of differentiated thyroid carcinoma. The assay of Tg is used for the early detection or exclusion of metastases, tumor relapses and the follow-up of radioiodine treatments. Serum Tg is no detectable in patients who underwent total thyroidectomy and are free of metastases and tumour. These patients in true complete remission will not display Tg levels, even by endogenous TSH stimulation.
Consequently detectable Tg values in this group of patients are an important indication for still existing or newly developed neoplasia, particularly if these detectable Tg values are increasing under a TSH-suppressive thyroid hormone treatment (Tg profiles). For this reason a high sensitivity assay test is very useful.
In case of patients that need an extended period monitoring, it is recommended to keep using the same analytical test, inserting in the same run the samples previously tested as well.
The presence of anti-Tg antibodies in the serum of the patient can influence the Tg assay.
Immunoenzymatic method for the quantitative determination thyroglobulin (Tg) in human serum, using a disposable device applied on the Chorus and Chorus TRIO instruments. The test is based on the ELISA principle (Enzyme Linked ImmunoSorbent Assay) which uses the reaction between the antibodies present in the tested sample and the immobilized antigen bound to solid phases.The immunoglobulins bind to the antigen through incubation with diluted human serum.The disposable devices contain all the reagents to perform the test when applied on the Chorus instruments. The results are expressed in ng/ml.