[Methods and clinical evaluation of a new enzyme immunologic method for determination of thyroxin binding globulin (TBG) and T4/TBG quotient: a multicenter study].

A heterogeneous enzyme immunoassay for the determination of thyroxine binding globulin (TBG) was developed and assessed in clinical trials in 12 laboratories. The assay is based on the competition principle and employs plastic tubes coated with goat anti-TBG. CV's between 1.4-8.9% for intra-assay precision and 2.9-8.6% for inter-assay precision were found over the concentration range of 4-40 mg/l TBG. In comparative studies using highly purified TBG as standard, values with Enzymun-Test TBG were found to be on average 30% lower than those obtained by various TBG-RIAs. A broad-base study, to determine reference values, was carried out on a group of control persons 18 to 50 years old without previous history of thyroid disease. This study revealed a median of 14.33 mg/l TBG, with 95% of all values between 9.6 and 18.5 mg/l TBG. The median in women of 14.5 mg/l TBG was significantly higher than in men (13.4 mg/l TBG). TBG values in hyperthyroid patients were within the reference range while those in hypothyroid individuals were elevated. Highly elevated TBG values were seen in women receiving oestrogen (median: 22.2 mg/l TBG) and in pregnant women (median: 28.5 mg/l TBG). The T4/TBG ratios made it possible to distinguish between euthyroid, hyperthyroid and hypothyroic subjects (median: 4.9, 11.3 and 1.0, respectively). These ratios were significantly lower in pregnant women (median: 3.1) than in the control persons.