Human Cytokeratin 19 Fragment Antigen 21-1 ELISA Kit (A74189) employs the sandwich enzyme immunoassay technique for the quantitative measurement of human Cytokeratin 19 Fragment Antigen 21-1 in serum, plasma, tissue homogenates, and other biological fluids. An antibody specific for Cytokeratin 19 Fragment Antigen 21-1 has been pre-coated onto a 96-well microtiter plate. The standards and test samples are added into the wells and the Cytokeratin 19 Fragment Antigen 21-1 present in each sample is bound to the wells by the immobilized antibody. Following incubation, the wells are washed and then incubated with Biotinylated Anti-Cytokeratin 19 Fragment Antigen 21-1 Antibody, which binds the captured Cytokeratin 19 Fragment Antigen 21-1 present in each well. Following incubation, unbound biotinylated detection antibody is removed by washing, and an HRP-Streptavidin conjugate is added to the wells and the microtiter plate is incubated. Following incubation and washing, TMB substrate solution is then used to visualize the HRP enzymatic reaction by catalysis to produce a blue-coloured product that changes to yellow after addition of acidic stop solution. The density of yellow is proportional to the amount of Cytokeratin 19 Fragment Antigen 21-1 captured in each well. The concentration of Cytokeratin 19 Fragment Antigen 21-1 can then be calculated by reading the O.D. absorbance at 450nm in a microplate reader and referring to the standard curve.