Materials and Methods

We describe a new double-antibody enzyme immunoassay for thyroxin-binding globulin (TBG) in serum. A TBG-f3-o-galactosidase complex was prepared with m-maleimidobenzoyl N-hydroxysuccinimide ester. The mean analytical recovery of TBG added to serum was 99%, sample volume and TBG value were linearly related, and values for TBG determined by this method and those de-termined by radioimmunoassay correlated well (r = 0.98). Coefficients of variation averaged 7.6 % within assay, 6.6 % between assay. The measurable range of TBG in the serum was 3.3 to 52 mg/L, but higher TBG concentrations could be measured by diluting the test serum with TBG-free serum. Mean (and SD) serum TBG concentrations as de-termined by this method were as follows: for 20 normal subjects, 21.2 (3.7) mgIL; for 10 pregnant women, 50.1 (9.5) mg/L; and for 10 patients with TBG deficiency, not detectable. AdditIonal Keyphrases: 3-o-galactosidase doubleantibody radioimmunoassay #{149}TBG deficiency pregnancy referenceinterval Thyroxin-binding globulin (TBG) is the most important carrier protein in the serum for transport of circulating thyroid hormones. Therefore, determination of its serum concentra-tion is essential in evaluating the thyroid status of subjects with TBG abnormality. A specific radioimmunoassay for TBG is available (1) and has been widely used. However, a non-isotopic immunoassay, such as enzyme immunoassay (2, 3), would be preferableforroutinetests.Here we describea new enzyme immunoassay for TBG