What effects the TSH T4, T3 or both?

[Suesews]

This may sound like a stupid question but does anybody know what is actually responsible for your TSH level. Is the TSH level suppressed or elevated by the T4 or the T3 or a combination? If a combination then is there a ratio?

[diogenes Remembering]

The answer is: both T4 and T3 control TSH levels. FT4 does about 60% of the control and FT3 about 40%.

[Kell-E in reply to diogenes]

I'm not challenging what you said, but I have a question...why does the addition of T3 medication more readily cause suppression of TSH if most of the TSH control is attributed to FT4?

[diogenes Remembering in reply to Kell-E]

First, the effect of T3 and T4 on TSH, on the average, is nearly equal. I don't think there is any good evidence that T3 is more suppressive.

[Kell-E in reply to diogenes]

For me T3 is definitely more suppressive. (anecdotally I read this a lot) But I have had a total thyroidectomy, so there is no compensatory reduction in hormone production possible. Just a conversion reduction of T4 to T3 or an increase in RT3 from T4. The whole thing reminds me of the balloons they tie into shapes like poodles...you squeeze one end and the other gets bigger. Cellularly, if hormone transport is reduced or T3 receptors are occupied by RT3, then serum levels of FT3 and FT4 can rise, suppressing TSH too. So I guess the conclusion I come to is 'it depends'.

[shaws Administrator]

The TSH means Thyroid Stimulating Hormone and it is from the Pituitary Gland which, when the thyroid gland is beginning to fail and not sending out the appropriate quantity for our metabolism to work well, tries to flag the Pituitary Gland to produce more TSH - which rises.

This is a good explanation:-

endocrineweb.com/conditions...

Diogenes' response is far better than mine.

[Suesews in reply to shaws]

Hi Thanks, I am on Levo after a Thyroidectomy some 12 years ago and my docs are trying to reduce my dosage purely on the results of a low TSH. I was just wondering which part of thyroid replacement could be the cause of the suppression, and maybe an argument for taking a T4/T3 combo.

[shaws Administrator in reply to Suesews]

Well, if you've had a thyroidectomy they have no right reducing your dose due to your TSH.

There's no problem with suppression although some Endos/doctors have the wrong end of the stick. Some of us need a suppressed TSH to feel well.

Patients who have had thyroid cancer have to have a suppressed TSH and they don't come to harm. This is a previous post I did.

healthunlocked.com/thyroidu...

I think after twelve years of suffering you are entitled to a break and good health. I also think it should be standard to give T3/T4 to all thyroidectomised patients.

[Clutter in reply to Suesews]

Suesews,

The Levothyroxine dose you are taking is suppressing your TSH. Suppressed TSH does not mean you are over medicated as long as FT3 is within range.

Read Treatment Options in thyroiduk.org.uk/tuk/about_... Email [e-mail] if you would like a copy of the Pulse article to show your GP.

The only argument for T4+T3 combination is having low FT3 but it is very unlikely you will be able to get T3 prescribed on the NHS now.

[Suesews]

I have just got back from my appt with my GP. I asked why would you want to reduce my levo when my T4 & T3 are in normal range. She says that having a low TSH can affect the brain and the heart!! She also took my blood pressure and surprise, surprise it was a little high. I have never had high blood pressure until today.

I have had a reprieve until November, agreeing to leave it alone until then, hopefully my new regime of vits and minerals will have kicked in by then also.

[Treepie in reply to Suesews]

Could be white coat syndrome.Get a blood pressure monitor and record the results regularly to show the doc.

[Angel_of_the_North in reply to Suesews]

Ask her to prove it by citing a study that shows that low TSH causes those problems when not accompanied by over range FT4 or Ft3 (I'm pretty sure there aren't any). And how does it affect the brain?

[Suesews in reply to Angel_of_the_North]

I think she is just grasping at straws, trying the frightning tactic.

[Angel_of_the_North in reply to Suesews]

I can never understand why these doctors don't want their patients to feel well. Why do they need to scare them? If they don't want to prescrib something why don't they just say "Not doing it 'cos I don't want to, go somewhere else"?