Will leaving a 12 hour gap after a 12.5mcg dose of T3 before a TSH test be likely to spark it out of a suppressed (0.01 ) state?

[WildDeer]

I've been on T3 only for 12 years, helped to transition from levothyroxine after years of increasing illness by Dr Peatfield.

It's not perfect, but I have an active life and am well used to managing my levels and my health in general.

For the last 2years my TSH at annual review comes out as suppressed and my T3 high after a 9 hour gap.

I'm cetainly not overdosing. I never take the next dose until my pulse is below 65, and all my bloods came out mid range. I take between 50 and 62.5 mcg daily.

In the face of defensive hostilty from GPs at 2 different surgeries over the years I have been backed up by an NHS Endocrinologist who has an understanding of T3 for the last 5 years, but he now wants me to re-test with a longer gap.

I'm concerned I'll become rather hypo after 12 hours.

Can anyone explain why a TSH of 0.04 is considered OK , but 0.03 less than that is not in someone on long-term T3 treatment?

[tattybogle]

Can anyone explain why a TSH of 0.04 is considered OK , but 0.03 less than that is not..

i suspect someone got the numbers from the research paper in this post ( however it's actually about TSH on levo, not T3) : healthunlocked.com/thyroidu... useful-evidence-that-tsh-between-0.04-0.4-has-no-increased-risk-to-patients-on-levothyroxine-updated-new-study-does-show-small-risk

sadly the full paper now seems to be behind a paywall.

Regarding 12 hrs gap from last dose T3 ..... i doubt your TSH will rise at all with a 12 hr gap,,, if it's been supressed for years on T3 , it could take weeks/ months to rise even if you reduced dose substantially.

[Regenallotment Ambassador]

Google's AI tool found some useful responses to me asking, 'How long does T3 suppress TSH for' I've linked the most useful one, but listed the top 4 for you.

Drugs.com T3 is cleared from the body in around 6 days

Thyrogen - in the context of raising TSH for radioactive iodine (RAI) treatment can take 4-6 weeks to rise after stopping treatment (I'm assuming this is combination therapy)

NIH article 1. - TSH normalisation 6 months after stopping treatment (again I'm thinking combination therapy)

NIH article 2. - probably the most useful, suggests hypothyroid patients will clear thyroid hormone slower than euthyroid (1.38 days to 1, hyperthyroid even faster 0.63 days).

Link here ncbi.nlm.nih.gov/pmc/articl....

[WildDeer in reply to Regenallotment]

Thank you for seeking out all that information. So if I were euthyroid my TSH would be at its lowest after 12 hours!

[tattybogle]

it sounds to me like your endo is wanting to see if your fT3 is in range at 12 hrs, (since it's over range at 9 hours )

it's the fT3 level that will be different if you test at 9 hrs / 12hrs .....not the TSH ... in all likely hood the TSH won't be any different .

[SlowDragon Administrator]

Many members on T3 or Levo plus T3 have TSH below 0.03

TSH won’t change if you leave 12 hours between last dose T3 and test

Why there’s a time lag on TSH changing….and might not ever change if been suppressed long time

healthunlocked.com/thyroidu...

Why TSH is sluggish - mechanism called 'Hysteresis'.

healthunlocked.com/thyroidu....

starts at the end of the first reply from tattybogle

“To understand why TSH stays suppressed for a long time after an episode of hyperthyroidism/ overmedication, (or ANY T3 use) has finished... "

and is continued in detail much further down in another reply : " CONTINUED HYSTERESIS ~ Why TSH remains lower for quite along while following episodes of hyperthyroidism / overmedication .... (or any T3 use) , it is due (at least partly) to a mechanism called 'Hysteresis'.

Do you test and supplement to maintain good vitamin levels

[WildDeer in reply to SlowDragon]

Thanks for this info. I supplement with Thorne Basic B, Selenium, zinc and magnesium. Also Vit D3. I was diagnosed with diabetes 2 in 2022 and am keeping it under control with low carb diet. I need to check my vitamin levels again I realise.