In a competitive ELISA, a positive test result is indicated by:
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 c
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.