A simple ligand-binding assay for thyroxine-binding globulin on reusable Sephadex columns.

Area of Science:

• Endocrinology
• Biochemistry
• Clinical Chemistry

Background:

• Thyroxine-binding globulin (TBG) is a key protein in thyroid hormone transport.
• Accurate measurement of TBG is crucial for diagnosing thyroid disorders.
• Existing methods for TBG assay can be complex or time-consuming.

Purpose of the Study:

• To develop and validate a simple, rapid, and precise method for thyroxine-binding globulin assay.
• To evaluate the performance of the new method in various clinical conditions.

Main Methods:

• Utilized reusable Sephadex G-25 (fine) columns for the assay.
• Employed elution with diluted iodothyronine-free serum to separate protein-bound [125I]thyroxine.
• Established conditions to abolish binding to thyroxine-binding prealbumin and albumin.

Main Results:

• The method demonstrated simplicity, rapidity, and precision, suitable for large-scale sample analysis.
• Established normal TBG values (31.6 ± 5.4 mg/l) and provided values for hyperthyroid (28.3 ± 4.8 mg/l), hypothyroid (40.6 ± 7.5 mg/l), oral contraceptive users (40.1 ± 6.8 mg/l), pregnant individuals (50.3 ± 5.4 mg/l), and cirrhotics (20.7 ± 4.3 mg/l).
• Observed decreased TBG concentrations in heated serum (56°C) with increased [125I]triiodothyronine uptake, showing a negative correlation.

Conclusions:

• The described Sephadex G-25 column method is a reliable and efficient tool for TBG quantification.
• The assay provides valuable insights into TBG variations across different physiological states and diseases.
• Findings suggest a relationship between TBG levels, triiodothyronine uptake, and serum heat treatment.