Thyroxine binding globulin (TBG) and thyroxine binding prealbumin (TBPA) measurement, compared with the conventional T3 uptake in the diagnosis of thyroid disease.

An electroimmunoassay for the determination of thyroxine binding prealbumin is described. The diagnostic efficiency of the assay when used in conjunction with the serum thyroxine as a thyroxine: thyroxine binding prealbumin ratio, is compared with the conventional free thyroxine index and the more recently developed thyroxine: thyroxine binding globulin ratio. The population studied included euthyroid, hypothyroid and hyperthyroid patients and also those who were either pregnant or receiving oral contraceptive therapy. Despite recent evidence establishing the theoretical/practical advantages of using a direct measurement for thyroid binding proteins rather than an indirect method (tri-iodothyronine uptake), results obtained from this study suggest that, for the majority of patients requiring biochemical assessment, the free thyroxine index is still the superior discriminator of thyroid abnormality.