NDT and when to take a blood test

[AleB]

Dear All, as I am a relative newbie to NDT (8 weeks tomorrow). Could anyone offer advice about what time I should do a blood test (previously on Levo I was off it for 24hrs before blood test). I take 2 grains all at once at 6am! Thanks for any advice.

[SeasideSusie Remembering]

AleB

It's recommended to take last dose of NDT 8-12 hours before blood draw. Because of the T3 element in NDT, the FT3 result is the most important. T3 starts to leave the blood after 12 hours. If you leave any longer than 12 hours between last dose and blood draw the result will show a false low, take your NDT too close to the blood draw then you will get a false high FT3.

You could adjust the timing of your NDT the day before your test, maybe take half your dose at the normal time and the other half in the evening.

[AleB in reply to SeasideSusie]

Hi SeasideSusie, thank you for your response. Right, that means that my last blood test was a false low for T3 as I had gone 24hrs! The endo wants a timed blood within 2 hours of taking it, but this will give a false spike surely, he already thinks that I am euthyroid because I am taking 2 grains as opposed to the 1 & 1/2 grain he prescribed. I increased on the 25th April after results being low for T3 3.4 range 3.50- 6.50. Today I am going to split the doses up and try to see if this helps with fatigue and pain. The reason I increased was because I felt completely rubbish, sleeping all the time no energy.

[SeasideSusie Remembering in reply to AleB]

AleB

The endo wants a timed blood within 2 hours of taking it, but this will give a false spike surely

If you fancy a bit of reading, I've included a couple of links below, talking about T3 and NDT.

ncbi.nlm.nih.gov/pmc/articl... - talks about peak T3 levels 2-4 hours after T3 administration and reaches baseline afte 12 hours.

emedicine.medscape.com/arti... - tells us that oral absorption of thyroid hormone can be erratic (T4 up to 80%; T3 up to 95%) and decreases with age. The time for peak serum levels is 2-4 hours.

So why would an endo want to use the peak level as a guide to dosing, the level is at it's peak for a short time then decreases so surely using the normal circulating level is a better guide to dosing. But at the end of the day the goal is relieve symptoms, so these should also be taken into account.

Today I am going to split the doses up and try to see if this helps with fatigue and pain.

Some people are fine with dosing once a day, some need to split the dose if they get a slump later in the day when the T3 level gets low. We're all individual and have to find what suits us best. I take Levo and T3 in one dose in the early hours of the morning when I need the bathroom - between 3 and 6am usually. I did split the T3 dose to start with but when I experimented I found no difference in how I felt if I take it in one dose.

The reason I increased was because I felt completely rubbish, sleeping all the time no energy.

When taking NDT (or a combination of Levo plus T3) one would expect to see a low, even suppressed, TSH, possibly a lowish FT4 and FT3 in the upper part of the range if that is where you feel well.

[radd in reply to AleB]

AleB,

I always test two hours after taking NDT as per my endos instructions, to ensure my T3 peaks aren’t going over range.

I have long term Hashimotos and absolutely no thyroid gland left. I am sensitive to thyroid meds and operate well on just 1.5 grains WP Thyroid.

If sex hormones have been previously messed up, I have learnt there is a fine T3 margin and it is vital not to take too much.

[greygoose]

The most important number - especially on NDT - is the FT3. The FT4 will be low, anyway, because of the T3 in the NDT, so it doesn't really matter if you only leave 8 - 12 hours.

[AleB]

Thank you for your response Scrumbler, by my calculation then of the 20% to my T3 is 4.08 which on the range I have 3.50 - 6.50 is still not optimal. My T3 was 3.4, I think If I try splitting the dose throughout the day and then take my last dose 12 hours before a timed blood test this may give me a starting point.

[Hidden]

thyroidresearchjournal.biom...

This guidance for endos suggests 2-4 hrs post dose to see peak levels. It suggests this as safest way to avoid overtreatment. There are links to the pharmacokinetics in references.

[Greekchick in reply to Hidden]

This is an excellent article and thanks for posting it! It will help me enormously as I am getting my meds adjusted post TT.

[Hidden in reply to Greekchick]

I found it very useful. I have read a lot of the references too, many of which were also very informative. Good luck! 😃