Radioimmunoassay of thyroxine-binding globulin in human plasma

Area of Science:

• Endocrinology
• Biochemistry
• Clinical Chemistry

Background:

• Thyroid hormones, thyroxine (T4) and triiodothyroxine (T3), are crucial for metabolism.
• Thyroxine-binding globulin (TBG) is the primary carrier protein for thyroid hormones.
• Understanding TBG levels across different age groups and thyroid states is essential for accurate diagnosis.

Purpose of the Study:

• To develop and validate a highly specific radioimmunoassay for thyroxine-binding globulin (TBG).
• To investigate the relationship between TBG, thyroxine (T4), and triiodothyroxine (T3) levels across different age groups and thyroid conditions.
• To establish age-dependent reference ranges for TBG to improve clinical discrimination of thyroid function.

Main Methods:

• Development of a specific radioimmunoassay for TBG, excluding cross-reactivity with albumin and prealbumin.
• Measurement of TBG, T4, and T3 levels in young adults, children, the elderly, and patients with hyperthyroidism and hypothyroidism.
• Correlation analysis of TBG levels with age, T4, and T3 concentrations.

Main Results:

• A precise radioimmunoassay for TBG was established.
• TBG levels were found to be elevated in childhood (1.34 mg/100 ml) and old age (1.28 mg/100 ml) compared to young adults (0.97 mg/100 ml).
• While TBG correlated with T4 in normals and children, T4 and T3 showed a progressive decrease with age, independent of TBG. TBG was elevated in hypothyroidism and mildly increased in mild thyrotoxicosis.

Conclusions:

• TBG levels do not consistently decrease with age, unlike T4 and T3.
• Age-dependent reference ranges for TBG are necessary for accurate clinical interpretation of thyroid function tests.
• Further research into the dependence of TBG on thyroid hormone concentrations is warranted for understanding thyroid hormone production and kinetics.