This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology, Subject name: Microbiology
Most sensitive test for antigen detection is - 
Select and explain. 
A. RIA, B. Elisa, C. Immunofluorescence, D. Passive hemagglutination
A: RIA
Answer: A: RIA 
Explanation: RIA is a competitive binding assay in which fixed amounts of antibody and radiolabelled antigen react in the presence of unlabeled antigen. The labeled and unlabeled antigens compete for the limited binding sites on the antibody. This competition is determined by the level of the unlabelled antigen present in the patient's serum sample. Reference : Anathanarayan & paniker's 9th edition, pg no:113 <\p>