Question

Effect of oral estrogen on thyroid levels:

a) Decreases TSH, increases total T4, decreases total T3
b) Increases TSH, increases total T4, decreases total T3
c) Decreases TSH, increases total T4 and T3
d) Increases TSH, decreases total T4 and T3

Answer 1

Administering oral estrogen increases thyroid-binding globulin, which increases the levels of total T4. This change does not significantly alter free T4 and T3 levels due to the body's regulatory negative feedback loop, and thus TSH levels are not likely to increase, leading to the conclusion that option 'b)' is the correct answer.

Step-by-step explanation:

Upon administering oral estrogen, it may influence thyroid function tests by increasing the thyroid-binding globulin (TBG) levels. Due to this, the levels of total T4 and total T3 bound to TBG in the bloodstream would increase. However, because the body maintains a negative feedback loop to regulate thyroid hormone levels, an increase in total T4 does not result in a significant change in the free T4 and T3 levels, which are physiologically active.

As free T3 and T4 levels remain generally constant, the anterior pituitary gland does not detect a significant change in thyroid hormone levels. Hence, TSH levels are unlikely to increase. Therefore, the correct option that describes the effect of oral estrogen on thyroid levels is 'b) Increases TSH, increases total T4, decreases total T3.'