1881 – SELco® FT4

The SELco® FT4 is a quantitative immunoassay for the determination of free Thyroxine (FT4) in human. The SELco® FT4 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. As clinical hint, serum level of free T4 (FT4) correlates with secretion and metabolism rates of T4, and hence has been recommended as a reliable and significant diagnostic indicator of thyroid diseases, especially in ambiguous or borderline cases.

Radioimmunoassays based on coated tube technology are widely used for the determination of specific antigens. The SELco® FT4 immunoassay is based on a competitive reaction of free T4 in the patient´s sample and T4 immobilized on the inner surface of the tubes. A limited amount of a monoclonal antibody directed against T4 conjugated with Iodine-125 (tracer) detects the coated T4 on the surface of the tubes as well as the free T4 (FT4) in the sample. The concentration of FT4 in the sample influences the antibody activity binding to T4 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 FT4 concentration in the sample.

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