This standard specifies the classification, requirements, test methods, identification, labels, instructions for use, packaging, transportation and storage of total thyroxine quantitative labeling immunoassay kits. This standard applies to kits for the quantitative determination of total thyroxine (TT) based on the principle of competition method (hereinafter referred to as: TT kit). It includes immunoassay kits for quantitative determination of TT using labeling methods such as enzyme labeling, (electro) chemiluminescent labeling, (time-resolved) fluorescent labeling, etc., and microplates, tubes, magnetic particles, microbeads and plastic beads as carriers. This standard does not apply to: a) colloidal gold-labeled TT test strips; b) various types of TT radioimmunoassay or immunoradiation kits labeled with Class I radioactive isotopes.