Suspected underactive thyroid or hypothyroidism

[sunshineisbetter]

I have further blood tests in the next few weeks due to suspected underactive thyroid or hypothyroidism based on the results of these blood tests.

I have managed to access my blood test records online.

What does Serum free T4 mean?

What is Serum free T4 correlation to TSH levels?

How do they typically relate to each other?

[tattybogle]

T4 is one of the hormones produced by thyroid gland.

Free T4 is how much of it is 'unbound ' and available in the blood.

TSH (thyroid stimulating hormone) is a message from pituitary to thyroid asking for more or less T4 (and T3 - the other thyroid hormone) to be produced.

Easy way to remember how they relate :-

imagine TSH and T4/3 on opposite ends of a see-saw.

As T4/3 go lower... TSH rises.

As T4/3 go higher ... TSH lowers.

TSH is both responsive to T4/3 levels , and also drives them.

Lower T4/3 causes pituitary to produce more TSH.

Higher TSH drives thyroid to produce more T4/3.

If pituitary senses really high levels of T4/3 , then it stops TSH production completely . TSH becomes supressed (so low it's unmeasurable)

Thyroid is no longer stimulated by TSH , and so stops releasing T4/3

Most peoples 'Normal healthy' TSH is around 1 or 2, (but not every one)

It's a complex finely tuned system , and it's purpose is to try to maintain the active thyroid hormone (T3) at a stable level. TSH can alter the ratio of T4 to T3 that the thyroid produces, and can also speed up conversion of inactive T4 to active T3 in the target cells of the body.