Practice question

Competitive ELISA is advantageous for small molecules, haptens and subtle structural differences that cannot accommodate two antibodies simultaneously in sandwich format. One antigenic site allows competition between labeled reference and sample antigen for limited antibody. Minor variations in epitope structure alter competitive displacement curves, enabling discrimination of analogs, drug metabolites, hormone isoforms and pesticide residues. Antibody subclass identification needs isotype specific secondaries, protein folding requires biophysical methods, cell counting needs cytometry. Sensitive competition reveals small antigenic differences undetectable by direct binding alone.