Good morning all
My understanding is when on NDT you should test 12 hours after your dose. Is that correct? If so at that point is the blood test more realistic as an indication of how well you are doing? I ask this because at my last one I was only a third way through the range of T3.
Hello again :
On NDT you dose to the relief of symptoms since there are no blood tests designed specifically for this thyroid hormone replacement.
If you need to do a blood test to be in the ranges it is suggested that you arrange the blood draw around 12 hours from your last dose
The blood test is just a snap shot in time and generally runs a few weeks behind actual symptoms and if you are still with some symptoms of hypothyroidism -
Do you monitor yourself on pulse, blood pressure and core temperature twice daily -
if so what sort of readings are you now getting ?
Jodypody,
Many on Levo (& T3) are testing to appease a GP’s beholden TSH values and a need to hold on to meds.
Blood testing regarding NDT is subjective because we are usually self medicating so can test when we want to, as long as the tests are like-for-like. I test 24 hours after last dose purely for ease.
However, the general forum consensus regarding T3 combining meds (including NDT) is to test between 8-12 hours after last dose to accomplish the average levels. Also to split T3 containing meds into 2 before the day of the blood draw.
I’m not sure where this has actually came from ... helvella , SlowDragon , SeasideSusie .. .. ... have we scientific proof backing this, or has someone just done some maths relating to the hormones half lives?
The basis for testing at certain times is simple.
After taking T4 or T3, or a combination, the blood levels rise sharply. Typically around two hours or so after swallowing.
Then they fall away.
The rise from swallow to peak is meaningless. It depends on dose taken and rate of absorption which could well vary from one make to another, even from one day to another in an individual.
The sharpness of that peak is such that there is no way of measuring that - five minutes can see a measurable drop from peak.
So we are on the long slope - going from steep drop to fairly shallow, almost flat, approaching the next dose.
But where on that do we measure? Anywhere from the peak to taking next dose is a slope. The only bit that you can readily predict is the flattest bit - hours after taking the dose and approaching the next dose. The trough.
Using trough measurements is common enough in medicine. Largely for these same reasons.
But endocrinology seems to assume that the levels of thyroid hormones are flat - all day, all night, every day, every night. Despite evidence to the contrary.
Of course, a TSH test done on someone who is profoundly hypothyroid (and untreated) will be high whenever it is done. Of course, another TSH test done on the same person when treated will be lower.
But time of day, and time from doses, matter when you try to compare a test on one occasion to a test done on another occasion. Especially as levels respond - TSH drops, FT4 and FT3 rise and all three could be within reference intervals.
Yes, we know all that hel, 😬 ... and I fully agree.
This question is asked a lot and given the complexities of the maths, it would be good to evidence the suggestions with credible source.
therefore, my question was do we (the forum) have official data or just what knowledgable members have gleaned from half life reading. For instance is there anything in the Thyroid UK info?
1) There is plenty of evidence of what happens to TSH, FT4 and FT3 levels - for example using sequential tests in individuals.
2) There is plenty of evidence that endocrinologists widely ignore time (of day and with respect to doses).
Isn't it just putting the two together?
Which, given 2), simply doesn't get done most of the time.
And for those who suggest that a trough level is not useful/sensible, I think it important to consider that a low trough thyroid hormone level could be seen as implying the person going into hypothyroid state every single day!
I agree with all you say hel and have quoted those same guidelines myself numerous times
Then this morning it struck me that experiences are subjective but for every factually suggestion we should be able to back up with credible source and not just complicated maths (as could actually be blagging 🤣🤣).
As this question comes up time and time again if there is no known believable source, eg Thyroid UK, diogenes, Barry Peatfield or Paul Robinson, would it be in members interest for you to make a sheet simplifying the process so members understand as opposed to blindly accepting a statement or calculation that many can't make head nor tail of.
Perhaps add it to your little black book kept about your person 👏 🤗
I reckon Helvella's little black book is to big to keep about his person , probably needs a wheelbarrow lol.
personally i think pictures explain it better than maths .
NOTE ~These graphs are unfortunately for Levo only/ Levo + T3 ( not NDT , am not sure anyone has done any for NDT)
Top graph (fT3) ~ top line shows how fT3 changes for Levo +T3, (bottom line shows Levo only)
Middle graph (fT4) ~ bottom line shows how fT4 changes for Levo + T3 , (top line shows Levo only)
(can't remember which paper i got the pictures from ,sorry)
Tatty Am I correct in assuming that the graphs show once daily dosing?
If I split my doses, as I do with a 16 hour gap and an 8 hour gap then my peak will not be so high and my lowest point/trough will be at the 16 hour mark before it starts to rise again with the next dose.
This is why I consider dosing patterns to be important in the timing of blood tests and the interpretation of results.
Yes .. one dose .
With 2 x smaller doses you'd expect the peaks to be smaller. (i think )
Also if using NDT rather than Levo +T3 ,i think you might expect to see a more even level overall ? without such big peaks
due to the T4 and T3 in NDT being bound to the thyroglobu ~thingywhotsits ... eg NDT being a 'sort of' slow release form of T4/T3 ?
perhaps ?
Well said Tatty! That's what I thought.
Hi Helvella
Funny but I still haven’t got a straight answer to my question 😂😂. All I wanted to know was is only a 1/3 way through the range to be expected or was I right to increase?
Jody there is no simple answer. Your ft3 was a third through range so yes if you are still symptomatic perhaps there is room for an increase. However where was your ft4 level? With NDT you are automatically increasing ft4 at the same time. This is why some folks on NDT find that they have to add in a little levo or add in a little lioT3 to increase either ft4 or ft3 but not the other.
So simply put an increase in NDT would depend on where both ft4 and ft3 were.
hi radd. I tested after 10 hours of dose last time. Didn’t split day before, can’t be bothered it’s tricky 😊. I didn’t train that day (normally heavy weight lifting most days) to give worst case scenario and was only 1/3 way through range on T3. Therefore was I right to increase based on feeling lethargic, bloated etc. I’m finding that trying to hit the sweet spot keeps drifting. I’ve been happy on 3 grains for around 8 months and then suddenly I’m overdosing. Could be the grief from the loss of my father has stopped me working out as much. Who knows but I find myself having to start all over again.
Jodypody,
Your question invoked some good discussion this morning 😁, that might hopefully be helpful to others. I would think 10 hours would give a good average for T3 levels, so if only measuring a third of the way through range would indicate room for an increase.
However, grief should never be underestimated and so be mindful if you have functioned well on 3 grains previously for some time. It could be a temporary period which reverses as you get back to your life as before, eg start exercising, etc . Sorry to hear about your father.
You were right to increase with 1/3 of range after 10 hours. Mine would be over range if measured after 10 hours.I have read that people at first sometimes need a higher dose and then reduce after a while as it becomes too much for several reasons. The way I see it is that we keep adding more each day, even at the same dose and at some point our cells maybe got enough?
No T4 doesn't plummet. For example when I add 5mcg T3 to a daily dose my ft4 result goes down by only 0.5 numerically so say from 15 down to 14.5. Adding 7.5mcg of T3 to my 100gms of T4 reduced my ft4 by 10% from 60% through range to 50% through range.
NDT has an element of t4 and t3 so every time you alter your dose you alter your intake of t4 and t3. On combo we can alter the dose of t4 and the dose of t3 individually to find levels of ft4 and ft3 that suit us individually. Some folks find that they can manage with low ft4 if ft3 is high; other folks need both ft4 and ft3 in the top third of the ranges. It is an individual thing and it takes time, trial and error to find what suits us individually.
As I said previously some folks on NDT find that the fixed ratio of T4 and t3 in each grain makes it difficult for them to find the levels of ft4 and ft3 that suit them and they have to add in a little T4 or a little T3 to fine tune their dose to get ft4 and ft3 at the best levels for them.
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1st Blood Test on NDT
Blood test results on NDT
Advice on timing of NDT dose prior to blood test
Best time to take first NDT blood test 
