If a T4 dosage has been taken for six weeks and achieved initial result :
FT4 22.3 ( 12.1 - 20)
FT3 4.7 (3.7 - 6.8)
Let’s suppose that the patient continued with the same dosage of T4 and repeated his test after successive 6 weeks, new result showed :
FT4 18.6 (12.1 -20)
FT3 5.4 (3.7- 6.8)
Does the decrease of FT4 is because it’s been converted to FT3 ? can we exclude malabsorption issue ?
Depends on dose of L-T4 to some extent (whether thyroid is suppressed). This is pretty normal day to day fluctuations. Given T3 is about four times as potent (in the blood) as T4 you can see the overall hormone level is stable.
I just want to know if there is a negative correlation between FT3 and FT4 .
FT4 decreased from 22.3 to 18.6. > delta =3.7
FT3 increased from 4.7 to 5.4 > delta =0.7
As T3 is 4 Times stronger than T4 .. 3.7/ 4= ~ 0.7
Do you agree with this conclusion?
Generally fT3 is maintained mid-interval. However, when there is subnormal TSH secretion there seems to be an inverse relationship, at least from some data I collected. I will be posting on this within the next few weeks.
You would expect the results you calculate as the relative potency is based on the effects on TSH. I would expect a roughly similar TSH from both blood tests (allowing for normal diurnal and menstrual variations).
Inverse relationship ?
You mean when tsh is high, ft3 gets low ?
Last test :
TSH 14.4
FT4 18.6 (12.1 - 20.1)
FT3 5.4 (3.8 - 6.7)
Pre-last Test :
TSH 8.8
FT4 22.3
FT3 4.7
The interesting thing is that these two tests were with same LT-4 dosage
Should have been specific. I meant an inverse relationship between fT3 and fT4. This seems to happen sometimes although studies seem to show a more steady fT3. I wonder if your TSH figures are correct, they are quite high for your hormone levels, could be interference with the assay or sometimes low acitivity TSH isoforms can be produced although TSH is usually low in these cases. I would trust your TSH readings!
The laboratory where they analyzed the blood uses ECLIA Assay from roche :
Electrochemiluminescence.
There is something called tsh resistance, have you ever heard about it ?
I would want to know when the last dose of Levo was taken before both tests. To compare them accurately testing has to be done the same each time and it's advised here to always do the test at the same time of day and take last dose of Levo 24 hours before blood draw.
Yes same dose and has been taken before the test, however levothyroxin has been taken at 6.00 in the morning and test was done at 8 in the morning.
As for the second test, levothyroxin has been taken at 4.00 in the morning and test was done at 8 in the morning
Well, obviously the results aren't true circulating levels due to the fact that Levo was taken before the test but I realise that's not your point, although the second test being done 2 hours later will make a difference but not sure if it would be that much.
Have thyroid antibodies been tested?
Anti-tpo was 336 in the first test, the doctor didn’t order tpo in the second test !
Don’t you think there is a negative correlation between FT4 and FT3 ?
Why should I take levothyroxin before 24 hours ? Didn’t they say that LT-4 has up to 7 days life span ?
Freddyy
Anti-tpo was 336 in the first test, the doctor didn’t order tpo in the second test !
So if the range was what we normally see here for TPO antibodies, i.e. <34 or <60, then this confirms autoimmune thyroid disease aka Hashimoto's. Once confirmed there is no need to retest antibodies. Because antibody activity fluctuates with Hashi's, as and when the immune system attacks the thyroid, then results can fluctuate and I think sometimes strange results can't always be explained. I don't have Hashi's so this is not my area of expertise.
Don’t you think there is a negative correlation between FT4 and FT3 ?
I can't answer that question.
Why should I take levothyroxin before 24 hours ?
The reason for not taking Levo before a blood test is because the result will show the level of hormone in your blood from the dose recently taken. Levo peaks in the blood about 2 hours after ingesting. Taking your dose too close to the blood draw will give false high results, leaving any longer gap will give false low results. So it's always advised here, and by some endos, to take last dose of Levo 24 hours before blood draw. If taking T3 or NDT then the last dose should be 8-12 hours before the blood draw, this is because again T3 peaks in the blood about 2-4 hours after ingestion and starts to leave the blood after 12 hours.
Didn’t they say that LT-4 has up to 7 days life span ?
Levo has a half life of 7 days.
Great, thx for the information
Can I say that the improvement in FT3 ( increased from 4.7 to 5.4 ) is because of an optimized conversion ?
I am on gluten free and repairing my gut within some supplements.
Can I say that the improvement in FT3 ( increased from 4.7 to 5.4 ) is because of an optimized conversion ?
That may very well be, or if not optimised it may be better than it was.
I am on gluten free and repairing my gut within some supplements.
It would seem this might be helping. Also, optimal nutrient levels are needed for thyroid hormone to work properly and good conversion to take place. Having Hashi's often means that nutrient levels are low. If not already tested then the following really are needed and optimal levels are:
Vit D - 100-150nmol/L
B12 - at least 550pg/ml (or ng/L) for serum B12, for Active B12 then below 70 suggests testing for B12 deficiency, over 100 would be fine.
Folate - at least half way through range
Ferritin - recommended is half way through range although I've seen that good levels are - for females 100-130 and for males 150.
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