Why is TSH so useless if you have post Graves induced Hypothyroidism?

[sarah_p]

A few people have told me this but I don't really understand why. Is there a scientific reason for this? I know why TSH is generally a useless test but why specifically if you have Graves?

[PinkNinja]

It's not specifically if you have Grave's, it's any type of hypothyroidism. For some, it is a useful indicator but for many people it just isn't at all useful. TSH has been shown to not respond in the way it should once you have hypothyroidism therefore it is not a helpful test in many cases. TSH is a pituitary hormone which can be affected by many things other than thyroid which also makes it unreliable. It can be a useful indicator for diagnosis but only in some people and only in combination with thyroid hormone tests such as T4 and T3.

I hope that helps

Carolyn x

[sarah_p in reply to PinkNinja]

Thanks Carolyn!!

[PinkNinja in reply to sarah_p]

I'm sorry, Sarah. It has just been brought to my attention that there may also be a Grave's-specific reason to do with having had a suppressed TSH for a long time. It can take a while for the TSH to come back up once thyroid hormone levels are good so you can have great levels of thyroid hormones but still have a low TSH even if you are not on replacement thyroid hormones.

It is generally unreliable for a lot of people though.

[helvella Administrator Thyroid UK in reply to PinkNinja]

Agreed!

However, it should be noted that the TSH response may be suppressed for weeks or months by prior thyrotoxicosis; thus, the TSH level may not accurately reflect hypothyroidism in these persons and should not be used in preference to the FTI or FT4.

thyroidmanager.org/chapter/...

(Ignore reference to Free Thyroxine Index/FTI - think it is never done in the UK.)

Rod

[marram]

There was some ground-breaking research done in Amsterdam which presented strong evidence that there are TSH receptors in the Pituitary Gland.

These receptors would respond to high levels of TSH in the blood and would cause the Pituitary to reduce TSH production much faster than simply responding to the drop in output from the hypothalamus. In other words, these TSH receptors in the pituitary are a fast-response system.

If you have Graves' you have a form of antibody in your blood called Thyroid Stimulating Immunoglobulin (TSI) which is similar in structure to the TSH, except that it seems to be even more attractive to the TSH receptors that the TSH itself!

What would be the result of TSI hitting the TSH receptors in the pituitary? It would fool the pituitary into thinking that the blood was full of TSH, and thus shut down production of TSH. Giving you a false low TSH which has absolutely no connection with the true level of thyroid hormones in your blood.

This is an extract of the report:

ncbi.nlm.nih.gov/pubmed/116...

This reveals that the effect of Graves' lasts longer than the short-term effect of prior thyrotoxicosis, in fact as long as you have Graves' antibodies in your blood, your TSH will be falsely suppressed.

I had a total thyroidectomy over 30 years ago, yet a recent blood test revealed Graves' antibodies in my blood! I have had a recent mild attack of Thyroid Eye Disease and have been referred to a TED specialist.

I suspect that if you were to show this to your GP and ask that he test more than just the TSH he would scoff at you. But this really is evidence that the TSH is totally flawed.