What should FT3 levels ideally look like on NDT? - Thyroid UK

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What should FT3 levels ideally look like on NDT?


I realise this question may have been asked before, but I simply cannot remember where and when, so I hope it's OK to ask it again...

Could anyone please tell me what your FT3 levels should ideally look like ca 24 hours after taking NDT? On Armour (5 grains daily), they were just above the lower normal limit, which caused my doctor to switch me to Erfa. On Erfa, my FT3 levels have been at the upper normal range, or slightly above, but what do they look like the day before, that is, shortly after taking the pills...that must mean that the FT3 levels are quite high, even above the upper normal limit, and then drop quite drastically after 24 h, and before taking a new dose?

If FT3 levels are at the lower normal range 24 hours after taking Armour, does that not mean that they were much higher (maybe even twice as high) the day before, after taking the pills...that is, close to or at the upper normal limit?

7 Replies

Anna69, FT3 will ideally be in the top third of range. You can extrapolate your FT3 result by +20% if you leave 24 hours between last dose and blood draw ie FT3 5.0 +20% = 6.0.

FT3 levels can be elevated by 2 or 3 times normal level shortly after taking a dose.


I am not a medical professional and this information is not intended to be a substitute for medical guidance from your own doctor. Please check with your personal physician before applying any of these suggestions.

Hidden in reply to Clutter

OK, thank you, Clutter:-) My FT3 levels on Armour (5 grains daily) were 2.9 after 24 hours (ref 2.7-4.2), which I interpret to mean that they were suboptimal...? I will remain on Erfa, which is the only other NDT drug available in Belgium, and can only hope that I won't get a bad batch...OT, does it seem the problems with Erfa have now been solved, or are there still bad batches? Erfa of course continues to deny any reformulation...

Clutter in reply to Hidden

Anna69, It's possible to get a bad batch of any medication. I imagine people who have problems with Erfa or Armour despite the companies denying they have reformulated will have switched to other NDT.

Hidden in reply to Clutter

Yes, I know. What I meant was that Forest (previous manufacturer of Armour) has never denied the reformulation of Armour, whereas Erfa continues to deny any change to the formula...

Thanks again for your input, much appreciated:-)

Clutter in reply to Hidden

Anna69, a number of patients are dissatisfied with Armour since Actavis bought it in 2014 from Forrest but Actavis denied they reformulated Armour.

Parbrook in reply to Clutter

"You can extrapolate your FT3 result by +20% if you leave 24 hours between last dose and blood draw ie FT3 5.0 +20% = 6.0."

Very interesting, Clutter.

How precise is this calculation?

I am interested in applying this to my FT3 results and range as it would give more meaningful information, especially when discussing FT3 with my GP.

The timings of my blood tests are typically 27 to 29 hours from my T3 & T4 doses.

Clutter in reply to Parbrook

Yousurname, The information came from someone who has researched thyroid extensively. I have no links to substantiate the precision or veracity.

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