Practice question

Competitive ELISA follows an inverse signal principle where sample antigen competes with enzyme-labeled antigen for limited antibody binding sites. When target analyte concentration is high in specimen, it outcompetes labeled competitor, reducing enzyme retained after washing. Consequently substrate conversion declines and absorbance remains low. A strong color would mean labeled antigen successfully bound, indicating little or no competing analyte. Therefore disappearance or marked reduction of color signals positivity, allowing quantification of small molecules like hormones and drugs that cannot be sandwiched.