T4 dose causes no changes to FT4, but affects TSH

[lh22]

Hello all,

I've been taking T4 for quite some time now, and I've noticed that no matter what dose of T4 I take, my blood serum FT4 doesn't change. However my TSH does, and so do my cholesterol levels, so clearly T4 is working. Can anyone shed some light on why the FT4 levels don't seem to change much? Vitamins, nutrients etc are all within range.

Thank you

[SlowDragon Administrator]

How much levothyroxine are you currently taking

How long on that dose and which brand

Please add most recent results and ranges

Recommended that all thyroid blood tests early morning, ideally just before 9am, only drink water between waking and test and last dose levothyroxine 24 hours before test

This gives highest TSH, lowest FT4 and most consistent results. (Patient to patient tip)

[lh22 in reply to SlowDragon]

Thanks for the tips. I've been on thyroxine for a while and thanks to this forum, I've done what you mentioned before tests. The thing is I've had many tests done, and regardless of the dose of T4 I'm on, my FT4 doesn't really move from the lower end of the range. So I'm wondering why that is. TSH and other markers like cholesterol vary depending on the dose.

[SlowDragon Administrator in reply to lh22]

Well if you’re on high enough dose levothyroxine…..initially as you increase TSH drops at increase in dose …..then starts to creep back up and Ft4 will drop (and Ft3)

Same with cholesterol …..initially will drop, but if Levo dose isn’t high enough then slowly cholesterol will start to increase again

Typically takes 3-4 months for each dose increase to settle……or longer as you get near final correct dose

Guidelines on eventual dose levothyroxine is that majority of people need something around 1.6mcg Levo per kilo of your weight per day