– The test principle applied in this kit is Sandwich enzyme immunoassay. The microtiter plate provided in this kit has been pre-coated with an antibody specific to Human GDF15, and the Human GDF15 standard plate wells that pre-coated using protein-related techniques are provided separately. Standard/Sample Diluent Buffer or samples are added to the appropriate microtiter plate wells ,then added a HRP-conjugated antibody specific to Human GDF15. After TMB substrate solution is added, only those wells that contain Human GDF15 and HRP-conjugated antibody will exhibit a change in color. The enzyme-substrate reaction is terminated by the addition of sulphuric acid solution and the color change is measured spectrophotometrically at a wavelength of 450nm ± 10nm. The concentration of Human GDF15 in the samples is then determined by comparing the OD of the samples to the standard curve.