Understanding the role of TSH

[Windsinger]

Hi everyone From reading on this forum, I understand that if one takes T3 or NDT then TSH goes near zero and it is OK, as there is no need to convert T4 into T3... How about those who are on just T4? Do we still need some TSH to insure T4 to T3 convertion? And if so, then what is the optimal TSH level for that?

[diogenes Remembering]

1) There are two answers - one if you have some working thyroid left and the other- if you have none. 2) If you are on T4 only and have some working thyroid, its unwise to get totally suppressed TSH, but anything between 0.03-0.5 is fine, given a good FT3 result. TSH = 1 would be my top limit. 3) With no thyroid, some people need suppressed TSH to get sufficient hormone to convert to enough FT3. Others may not be able to achieve this at all with any amount of T4, so will need extra T3 to help out. In this case TSH may well be suppressed to undetectable. 4) Yet others will convert T4 to T3 well enough not to suppress their TSH. It's an individual thing and there are no hard and fast rules.

[Windsinger in reply to diogenes]

Thank you for such clear explanation. I think my case is number 4. I do have my thyroid, although sluggish, it is still kicking. To reiterate, TSH as little as 0.03 would still be enough to convert T4 into T3. Right? I am on Levo 50mcg. I will wait couple more weeks and then check my blood again. My last TSH was 0.48. I really appreciate all your help and support on this forum.

[Windsinger]

Very reassuring, thank you. If taking only T4, then we need some thyroid simulation/ tsh to help converting, I understand... With zero TSH I would have to add T3 . Am I getting it right?

[Windsinger]

Ah. That changes my idea of what's happening. Thank you. Much appreciated