TBG is a protein found in the blood necessary for the transport of thyroid hormone. High TBG levels are associated with high T3 and T4 levels; which is a false indication of hyperthyroidism. Low TBG blood levels are seen in people with low blood protein levels due to poor nutrition or decreased absorption of nutrients within the digestive tract, non-functioning ovaries, cancers that produce testosterone, kidney disease, or during periods of major stress. High TBG blood levels are seen in people with hormone replacement therapy (estrogen), hepatitis, inherited diseases that cause high levels of TBG, cancers that produce estrogen, oral contraceptives, or during normal pregnancy. There are many medications that affect levels of TBG.
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