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Thyroxine (T4)

Posts: 6
Joined: May 2005

What are normal levels of Thyroxine (T4). I have been told that mine is 14.6 and that normal is anywhere from 5-12. Is this correct even with thyroid cancer patients? In 2/05 I had a total thryoid removal and later had radioactive iodine treatment. I was going to an endo, but was later told that my family doctor could handle long term care. I guess I just get a little nervous that my family doctor will not know how to interpret my test results. I have to go to follow up visit, but I just wanted to know what this T4 level meant before going into the appointment. Please help.

Rustifox's picture
Posts: 110
Joined: Mar 2005

The most important number here is you TSH level, cmolina. I know this is confusing - I was very confused about it, too, when I was first diagnosed.

TSH and T4 levels are like a teeter-totter - if your TSH is low, (as it should be with thyroid cancer suppression - it should be generally no higher than .50 in a low risk thyroid cancer patient, and even lower - less than .10 or even down to .01 in a high risk patient) then your T4 level SHOULD be quite high.

If you think of this like a well, when your "well" is "full" of T4, it prevents the body from making TSH.

So the T4 level is supposed to be high - this means you have lots of thyroid hormone in your body, forcing the TSH down.

It is absolutely normal for a very low TSH (which we need, because the TSH 'feeds" thyroid cancer tissues)to expect a high T4 level, which makes sure the TSH doesn't rise - here is a study that explains why we do this (there are also more links about this topic on my personal webpage here on CSN):

So, the most important number here is your TSH level. Your TSH should be no more than .50 - or even lower, depending on your personal risk factors.

And as long as your TSH is low enough - below .50 - or below .10, if you have high risk factors, (as low as .01, even!) - then your doctor is doing the right thing... and by the sounds of your T4 being high, it is quite likely your TSH is within those low ranges.

Hope this makes sense for you - High T4 = low TSH; and low TSH is a very good thing for us.

A very low TSH (and high T4 level) can sometimes cause 'hyper' symptoms, though - like heart palpitations, etc when our T4 level is very high, but these can be dealt with by a very low dose of beta blockers, too.

If you have any types of heart problems, it is best to discuss your TSH/T4 levels with an endocrinologist and/or your cardiologist... Low TSH/high T4 can sometimes be hard on our hearts, but is definitely best as far as dealing with our cancer issues. All the best to you!

Posts: 6
Joined: May 2005

Thank you for your information. I am now better prepared for my appointment on Monday.

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