Free Triiodothyronine (FT3) ELISA

The ALPCO Free Triiodothyronine (FT3) ELISA is a competitive immunoassay. Competition occurs between an unlabeled antigen (present in standards, controls, and samples) and an enzyme-labelled antigen (conjugate) for a limited number of antibody binding sites on the microplate. The washing and decanting procedures remove unbound materials. After the washing step, the enzyme substrate is added. The enzymatic reaction is terminated by addition of the STOP solution. The absorbance is measured on a microplate reader. The intensity of the color formed is inversely proportional to the concentration of fT3 in the sample. A set of standards is used to plot a standard curve from which the amount of fT3 in samples and controls can be directly read. The labelled T3 (conjugate) employed in this assay system has shown no substantial binding properties towards thyroxine binding globulin (TBG) or human serum albumin (HSA). The binding sites on the microplates are designed to be of a low binding capacity in order not to disturb the equilibrium between T3 and its carrying proteins. The assay is carried out under normal physiological conditions of pH, temperature, and ionic strength.