The ratio of thyroxine-to-thyroxine binding globulin approximates the concentration of free thyroxine.
thyroxine-to-thyroxine binding globulin ratio =
= (thyroxine in µg/dL) / (thyroxine binding globulin in mg/dL)
• normal ratio: 3-5
• The ratio is increased in hyperthyroidism, congenital thyroid binding globulin excess, and familial hyperthyroxinemia.
• The ratio is decreased in hypothyroidism, congenital thyroid binding globulin deficiency, and during the third trimester of pregnancy.
• The ratio tends to be unchanged with acquired changes in thyroid binding globulin due to parallel changes in thyroxine.
To read more or access our algorithms and calculators, please log in or register.
Specialty: Endocrinology, Clinical Laboratory