This kit is used for quantitative determination of total thyroxine (TT4) in human serum in vitro. Total thyroxine (TT4) is one of the two main hormones secreted by the thyroid gland, with a molecular weight of 777d, most of which is produced by the thyroid gland. The main function of TT4 is to promote synthesis and energy metabolism, increase basal metabolic rate and oxygen consumption, and promote growth and development. 99.97% of TT4 in blood binds to TBG and TBPA. The synthesis and secretion of TT4 are mainly controlled by hypothalamus and pituitary. TT4 is one of the indexes for the diagnosis and efficacy evaluation of hyperthyroidism and hypothyroidism.