Why TSH is suppressed or under range

[Lalatoot]

"As Silva and Larsen have shown, T4 is preferentially converted to T3 in the

pituitary to a greater degree than in the other tissues, so its TSH suppressive effect is greater than its

metabolic. Thus, Thyroxine replacement treatment of hypothyroid subjects aiming at a normal serum TSH

value may result in undertreatment"

hormones.gr/91/article/the-...

A few other useful nuggets in the conclusions too.

[diogenes Remembering]

This should be archived here at TUK, because it highlights a reason for the continual criticism that T3-only or combination treatment nearly always results in suppressed TSH so that the TSH-only diagnostic approach is obviously in error.

[SarahJane1471]

Thanks for this Lalatoot this is my problem at the moment TSH 0.04 and low in range FT4/FT3 despite 125 of Levo . Seems my FTs won’t increase. Good info