The Free Thyroxine CLIA Kit is designed, developed, and produced for the quantitative measurement of human fT4 level in serum samples. The assay utilizes competition law for testing. The calibrators, controls, or sample, monoclonal antibody to fT4 labeled with microparticles are mixed and incubated, forming an antigen-antibody immuno-complex. Acridinium ester labeled fT4 are added and incubated.Acridinium ester labeled fT4 unbound to the sample binds to the Magnetically microgranular fT4 antibody. After precipitation in a magnetic field, the supernatant is decanted, and then a wash cycle is performed to remove any remaining substances that are not bound to the magnetic microbeads. Subsequently, the washed compound is sent into the measurement chamber where trigger solution is automatically added to initiate a chemiluminescence reaction. The light signal is measured by a photomultiplier as relative light units (RLUs), which is inversely proportional to the concentration of fT4 present in the sample. The test result is automatically calculated by the system according to the working curve.