Carbohydrate Antigen 19-5 (CA19-5) BioAssay-ELISA Kit (Human) employs the competitive inhibition enzyme immunoassay technique. An antibody specific for Carbohydrate Antigen 19-5 (CA19-5) has been pre-coated onto a microplate. A competitive inhibition reaction is launched between Horseradish Peroxidase (HRP) labeled Carbohydrate Antigen 19-5 (CA19-5) and unlabeled Carbohydrate Antigen 19-5 (CA19-5) (Standards or samples) with the pre-coated antibody specific for Carbohydrate Antigen 19-5 (CA19-5). After incubation the unbound conjugate is washed off. The amount of bound HRP conjugate is reverse proportional to the concentration of Carbohydrate Antigen 19-5 (CA19-5) in the sample. After addition of the substrate solution, the intensity of color developed is reverse proportional to the concentration of Carbohydrate Antigen 19-5 (CA19-5) in the sample.