Human Vitamin D Binding Protein ELISA KitIn this assay, the VDBP present in samples reacts with the anti-VDBP antibodies which have been adsorbed to the surface of polystyrene microtitre wells. After the removal of unbound proteins by washing, anti-VDBP antibodies conjugated with horseradish peroxidase (HRP), are added. These enzyme-labeled antibodies form complexes with the previously bound VDBP. Following another washing step, the enzyme bound to the immunosorbent is assayed by the addition of a chromogenic substrate, 3,3,5,5-tetramethylbenzidine (TMB). The quantity of bound enzyme varies directly with the concentration of VDBP in the sample tested; thus, the absorbance, at 450 nm, is a measure of the concentration of VDBP in the test sample. The quantity of VDBP in the test sample can be interpolated from the standard curve constructed from the standards, and corrected for sample dilution.