Clinical Observations on Serum Globulin Thyroxine-Binding Capacity, Using a Simplified Technique*

Using a relative simplified and reproducible technique, the thyroxine-binding capacity of the serum was measured in normal subjects, in pregnant women, in cases of hepatic cirrhosis, hypothyroidism and hyperthyroidism, and in euthyroid subjects with subnormal and elevated levels of serum protein-bound iodine (PBI). In 103 normal subjects having serum PBI levels between 5 and 7 μg. per 100 ml., the mean value of the thyroxine-binding capacity was 19.1 μg. per 100 ml.; female subjects were not significantly different from male subjects in this respect. In 34 men with low PBI values (between 2 and 4 μg per 100 ml.), the mean was 13.9 μg- per 100 ml. In 33 pregnant women, both the thyroxine binding capacity and the PBI concentration were increased. They returned to normal or lower levels by the end of the fifth week post partum. Although the thyroxine-binding capacity was often slightly higher than normal in 20 patients with hepatic cirrhosis, no definite correlation was found between the thyroxine-binding capacity, PBI level and the presence of vascular spiders. The binding capacity was slightly elevated in 9 patients with myxedema, whereas it was normal or lower than normal in 13 hyperthyroid patients. In 10 of 14 female euthyroid subjects with abnormally high serum PBI values, the thyroxine-binding capacity was definitely elevated. The question of the physiologic importance of thyroxine-binding globulin is discussed.