Cisbio Bioassays offers an accurate immunoradiometric assay for thyroxine binding protein (TBG). The assay is based on the competition type principle. The short 30 minute incubation enables results to be obtained very quickly. Added to the dosage of T4, the TBG assay enables the calculation of the T4/TBG ratio, key to a differential diagnosis between hypothyroidism, euthyroidism and hyperthyroidism.