1301 – SELco® Tg 1 step

The SELco® Tg 1 step is a quantitative immunoassay for the determination of thyroglobulin (Tg) in human serum. The SELco® Tg 1 step is intended as an aid in the diagnosis of thyroid disorders in conjunction with other clinical and laboratory findings.

Thyroglobulin (Tg), an iodine containing glycoprotein and precursor of the thyroid hormones thyroxine (T4) and triiodothyronine (T3), makes up a major part of thyroid colloid. The biosynthesis of Tg is regulated by thyrotropin, the only thyroid tissue that can produce, store and secrete Tg; Tg is thus organ- and tissue specific. This specificity is the main indication of the Tg determination in monitoring differentiated thyroid carcinoma, essential in the early detection and exclusion of metastases or tumour relapses. This indication is also used in the follow-up of radioiodine treatments.

Serum Tg measurements plays a major diagnostic role in the management of patients with differentiated thyroid carcinoma (DTC) after treatment; measurable and increasing serum Tg levels are an early and reliable indicator of persistent or recurrent disease. Additionally, serum Tg measurements can be useful in the diagnosis of neonatal hypothyroidism. In hyperthyroid adults undetectable serum Tg suggests thyrotoxicosis factitia.

Increased Tg values relative to the reference range in healthy individuals are also observed in benign thyroid diseases. Other indications of increased serum Tg levels are found in various non-malignant thyroid diseases, e.g. Hashimoto`s thyroiditis, Graves` disease, and non-toxic diffuse goiter, although in these cases, the actual Tg levels do not relate to disease severity in these conditions.

Radioimmunoassays based on coated tube technology are widely used for the determination of specific antigens. The SELco® Tg 1 step immunoassay is based on a reaction of two monoclonal antibodies against thyroglobulin (tg), one biotinylated and another conjugated with Iodine-125. If thyroglobulin is present in the patient´s sample, the antibodies bind simultaneously to different epitopes of the antigen. The generated immune complex is detected by streptavidin coated on the inner surface of the tubes. Decantation of the reaction mixture allows for the simple separation of generated immune complexes on the surface of the tube from the reaction mixture. The radioactivity of the tube is measured and proportional to the thyroglobulin concentration in the patient´s sample.

The immunoassay is designed for manual professional in vitro diagnostic use.