Radioimmunoassay for normalized thyroxine with use of Sephadex columns.

We describe a reproducible radioimmunoassay, with use of Sephadex columns, for measuring normalized thyroxine. In comparison with a competitive protein-binding procedure, the present method is more specific because antibody rather than thyroxine-binding globulin is responsible for the competition between endogeneous and tracer thyroxine. In barbital buffer, various concentrations of thyroxine binding pre-albumin and albumin had no influence on the results. Values obtained by the present method correlated well with those by the free thyroxine index and a generally accepted thyroxine normalized method.