A Study of Thyroid Function in Partial Thyroxine-Binding Globulin Deficiency

Abstract

Objective: It is generally thought that thyroxine-binding globulin (TBG)-deficient individuals are euthyroid and do not require treatment. However, there have been case reports of TBG deficiency combined with hypothyroidism. The purpose of this study was to investigate the relationship between TBG deficiency and thyroid function. Methods: We reviewed the medical records of 32 patients diagnosed with TBG deficiency between 1997 and 2008 in Soonchunhyang University Seoul Hospital. All were partial TBG deficiency. Eighteen patients had combined hypothyroidism, and 14 patients had normal thyroid function. We compared the TBG, thyroid-stimulating hormone, free thyroxine, and total triiodothyronine levels between these 2 groups. Eighteen patients with TBG deficiency with hypothyroidism started thyroxine medication and continued for 2-3 years. After, they were followed up with thyroid function tests after discontinuing medication for 4 weeks at 2-3 years of age. Results: The TBG level in TBG deficiency with hypothyroidism patients was significantly lower than that in TBG deficiency with normal thyroid function (4.43± 2.22 mg/L vs. 6.23± 1.81 mg/L; P= 0.02). The percent TBG compared with normal mean TBG level according to age in the hypothyroidism patients was also significantly lower than that of patients with normal thyroid function (13.42%± 6.92% vs. 19.08%± 4.87%; P= 0.014). Sixteen of 18 patients diagnosed with TBG deficiency with hypothyroidism showed persistent hypothyroidism at 2-3 years of age. Conclusion: We conclude that TBG-deficient patients should be observed closely and undergo thyroid function testing in order not to miss hypothyroidism. More investigations of TBG deficiency and thyroid function are needed in the future.