Practice question

Radioimmunoassay is competitive binding assay where fixed amount of radiolabeled antigen competes with unlabeled patient antigen for limited antibody. Bound radioactivity is inversely proportional to patient antigen concentration. In type one diabetes low insulin secretion occurs due to beta cell destruction. With little cold insulin to compete, antibody binds predominantly hot labeled insulin, so precipitated complex retains high radioactivity counts. High insulin sample would displace hot insulin and lower counts. Therefore diabetic insulin deficient samples show low circulating insulin but high bound radioactivity reading, indicating hormone deficiency.