Assay performance and clinical validation of a radioimmunoassay for serum thyroxine-binding globulin

Abstract

A radioimmunoassay for the quantitation of serum thyroxine-binding globulin (TBG), RIA TBG (PEG) - INEP, was formed and characterised. Test sensitivity was found to be favorable (2.0 mg/L). The highly satisfactory precision of the assay was reflected in the low coefficients of variation (less than 5%) found for both intra- and interassay precision at three concentrations. Non-specific binding of the labeled antigen was less than 2% of the total binding. Linearity of the assay within the range of the standard curve (0-80.0 mg/L) was excellent (r =0.99) and the analytical recovery of TBG added to serum ranged from 91 to 115%. Reproducibility was checked by determining the concentration of TBG in samples of sera over a period of 32 days from the day of antigen iodination and F<Ftab 0.05, F0.05 7, 32 = 2.31. The assay was standardized for accuracy using Lyphochek Immunoassay Controls (Bio-Rad). A significant correlation was obtained between RIA TBG (PEG) and the Kodak Amerlite TBG Assay (r = 0.84; n = 25). The presented results show that RIA TBG (PEG) is a sensitive, precise and reliable method for determination of TBG in human sera. Assay reference ranges were established for sera from various subjects: euthyroid adults, hypothyroid and hyperthyroid patients and in healthy pregnant women.