Minimal effects of free fatty acids on the competitive protein-binding assay of serum thyroxine on reusable Sephadex columns

Procedure for a normalised thyroxine determination in small sephadex columns

A rapid simple test for measuring normalised serum thyroxine is described in detail, using small Sephadex columns. A small portion of test serum is reintroduced into the test system at the competitive binding stage, so that corrected T4 values are obtained when the concentrations of thyroxine binding globulin are variable. Only 125 microliter serum is required for the whole test. Values obtained by the present method correlated well with the product of thyroxine concentration and radioactive T3 uptake (T4--RT3U index) and with a commercially available method for normalized thyroxine (T4N). Day-to-day variation was CV=6%.