Thyroid Pathology

Question 1

Is T3 or T4 the active substance? More than 99% of all thyroid hormone is _________?

Answer 1

T3

Bound

Question 2

What are some reasons why Thyroid Binding Globulin would be up? Increased TBG levels leads to increase in what kind of T4 and T3? Does the free T4 and T3 stay the same?

Answer 2

Anything that increases estrogen activity (pregnancy, oral contraceptives, post-menopausal patient with estrogen replacement)

Total T4 and T3

Yes