1652 – SELco® FT3

The SELco® FT3 is a quantitative immunoassay for the determination of free Triiodothyronine (FT3) in human serum. The SELco® FT3 is intended as an aid in the diagnosis of thyroid diseases in conjunction with other clinical and laboratory findings.

The circulation of thyroid hormones (thyroxine, T4 and triiodothyronine, T3) is distributed into two compartments; a major protein bound one, and a minor free fraction. Alterations in the total thyroid hormone in blood may be due to changes of binding protein concentrations, or synthesis of thyroid hormone. Thyroid disorders then exist due to persistent change of free unbound fractions. This indication serves as clinical hint, in that total T4 and T3 is dependent on the knowledge of functional levels of binding proteins, measured at length. Thyroid gland triiodothyronine T3 is regarded as the most biologically active among the thyroid hormones produced in the thyroid gland; up to 80 % via de-iodination of T4 in peripheral tissues. Increase in free T3 (FT3) is generally associated with hyperthyroidism. In many cases, a single increased FT3 indicates a T3-thyrotoxicosis; hence as diagnostic tool, in the follow-up of patients who are subject to a therapy with triiodothyronine, the FT3 measurement is also necessary.

Radioimmunoassays based on coated tube technology are widely used for the determination of specific antigens. The SELco® FT3 immunoassay is based on a competitive reaction of free T3 in the patient´s sample and T3 immobilized on the inner surface of the tubes. A limited amount of a monoclonal antibody directed against T3 conjugated with 125-Iodine (tracer) detects the coated T3 on the surface of the tubes as well as the free T3 (FT3) in the sample. The concentration of FT3 in the sample influences the antibody activity binding to T3 on the surface of the tube. 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 inversely proportional to the FT3 concentration in the sample.

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