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Free T4, serum
Thyroxine, FT4
▪ 1st incubation: 9 µL of sample and a T4‑specific antibody labeled with a ruthenium complex.
▪ 2nd incubation: After addition of biotinylated T4 and streptavidin‑coated microparticles, the still-free binding sites of the labeled antibody become occupied, with formation of an antibody‑hapten complex. The entire complex becomes bound to the solid phase via interaction of biotin and streptavidin.
▪ The reaction mixture is aspirated into the measuring cell where the microparticles are magnetically captured onto the surface of the electrode. Unbound substances are then removed with ProCell II M. Application of a voltage to the electrode then induces chemiluminescent emission which is measured by a photomultiplier.
▪ Results are determined via a calibration curve which is instrument specifically generated by 2‑point calibration and a master curve provided via the cobas link.
Serum and Plasma Lithium Heparin
150 uL
Frozen
The free fraction of the circulating thyroxine (T4) is considered to exert the main influence on metabolic control. Consequently, the FT4 concentration is believed to be the most direct indicator of an individual’s thyroid status. FT4 concentrations are generally depressed in hypothyroidism and raised in hyperthyroidism. Measurement of FT4 thus provides an aid to the differential diagnosis of thyroid disease. FT4 concentrations are independent of the concentration of thyroid hormone binding proteins and may therefore be measured in patients with elevated or reduced binding protein concentrations without the need for additional tests of binding capacity. In borderline cases of suspected thyroid malfunction, additional tests such as free T3 or TSH may be necessary
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