What is a common cause of increased TBG levels in the body?

Increased levels of thyroid-binding globulin (TBG) in the body are commonly associated with estrogens. Estrogens stimulate the liver to produce more TBG, which increases the amount of thyroid hormone that is bound in the circulation. This binding is significant because it influences the availability of free thyroid hormones, which are the active forms that regulate metabolism.

During states of elevated estrogen, such as during pregnancy or with estrogen replacement therapy, TBG levels rise, thereby affecting thyroid hormone levels and leading to distinctive clinical evaluations. Understanding this relationship is crucial in clinical settings, particularly when interpreting thyroid function tests in individuals undergoing hormonal treatments or in those who are pregnant.

Although other factors like acute illness, anabolic steroids, and circulating thyroid hormones can influence thyroid function and levels of TBG, they do not have the same direct and established effect on TBG synthesis as estrogens do.