Nutrition
Thyroid Binding Globulin Basics
Thyroid binding globulin carries thyroid hormones in blood—pregnancy and estrogen can shift totals while free T4 remains the usual decision lab.
Thyroid binding globulin basics: TBG is a blood protein that carries most T4 and T3—when TBG rises or falls, total hormone levels change while free hormones may stay stable. Pregnancy, estrogen therapy, and some liver conditions alter TBG.
That is why clinicians prefer free T4 over total T4 for most decisions. Athletes on oral contraceptives should share that history at lab visits.
Misreading total tests causes unnecessary panic.
Common questions
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Do athletes need TBG tested routinely?
Usually no—free T4 and TSH cover most cases. TBG matters when totals and frees disagree or pregnancy and estrogen therapy change interpretation.
Related terms
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