Competitive ligand - binding assay for thyroxine binding globulin. Comparison with TBG radioimmunoassay and T3 uptake test.

A simple and reproducible competitive ligand binding assay has been utilized to measure serum TBG concentration. In euthyroid subjects TBG concentration (mean +/- SD, mg/l) was 33.7 +/- 4; hyperthyroid 24 -/+ 6; T3-thyrotoxicosis 20 +/- 7; hypothyroid 37 -/+ 7; pregnant 67 -/+ 18; post-partum period 59.8 -/+ 17; oral contraceptives 45 -/+ 7. The correlation of CLBA with RIA measurement of TBG was significant (p less than 0.001). The estimations of serum TBG by CLBA correlated significantly with T3 uptake test (p less than 0.001), but at higher concentration of TBG correlation was non-linear. T4 : TBG ration according to serum T4 and TBG concentration provided a reliable index in the assessment of thyroid function.