At last our latest paper is out in the European Thyroid Journal online:
Eur Thyroid J
DOI: 10.1159/000447967. This journal is very cagy about letting people have access to the whole text, but allow the summary. The essential findings are that in health, subjects defined by the FT3 normal range are not the same, independently of where they lie in the range. As you go up the range, you move from the good T4-T3 converters with low FT3 to the poor ones with high FT3. This has implications for later treatment and whether or not T3 will be needed when the thyroid fails. It suggests the need to monitor healthy people for their FT4, FT3 and TSH when well so as to discern the appropriate treatment should they fall ill later on. This would avoid the fruitless scratching about in ignorance by the GP/endocrinologist who otherwise wouldn't know your genetic makeup and its implications for how good or bad a converter you are, and therefore would have to start, as nowadays, without having appropriate information to treat with just T4 or with a combo of T4/T3. This paper continues the story of the variability and uniqueness of individuals in how their thyroid and body work together.
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diogenes
Remembering
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I didn't have any joy with accessing the summary but glad to read your synopsis. I was about to get my children tested (16yrs and 24yrs) for a baseline position. You have prompted me to do so. Thanks.
If you do, don't just archive the numbers. Also find the range of the tests. Then call the bottom number 0% and the top 100%. Calculate how far up the range you are as a percentage. Record that. This gets round the problem of range changes that might happen later because of instrument incompatibility and assay differences.
Sorry to be dim, but is the article saying that those of us with low in range FT3 are actually good converters and those near the top of the range aren't?
"As you go up the range, you move from the good T4-T3 converters with low FT3 to the poor ones with high FT3."
The reason is that people with low FT3 in the normal range are able to be healthy with this level, which means that they can use FT3 efficiently and that T4 need not be so strongly called on for conversion. The thyroid producing mostly T4 is thus not so involved in conversion because the body can cope. High in the range means that these require much more T3 to be healthy. The tissues themselves cannot provide all that is needed, so the thyroid has to step in to augment T4-T3 conversion to fill in the gap.
I am feeling slow in thought today ! Are you talking only about people who are not taking thyroid hormones of any description ? Is this before diagnosis ?
So after treatment has started, is there any way to differentiate low FT3 from poor conversion or undermedication from low FT3 because it's being used efficiently and more is not needed?
Thank you Diogenes for the explanation. However, what about those who are considered to be euthyroid by mainstream medics (and therefore 'healthy') who have a low FT3 level, but who have TSH levels over 3.5 or even 2.5 (with an upper range limit of 4.2) and have hypothyroid symptoms (and therefore considered by many non-mainstream medics as having undiagnosed hypothyroidism)?
Further to your explanation of T4:T3 ratio via-a-vis conversion, what result would be considered high (I'm afraid that ever since I became ill with ME I have had a kind of numbers 'dyslexia' so I find it difficult getting my head around some of this)?
And which values are being used (e.g. would it work with FT4:FT3)?
Low FT3 and TSH's over 3 indicate probably a poor converter whose thyroid is under strain if not actually hypo. The thyroid is failing to help the struggling tissues sufficiently. For reasonable converters on treatment, the FT4/FT3 ratio is about 3 to 4/1. Anything above 5 is suspiciously indicative of inferior conversion. This only applies to T4 mono therapy of course. It doesn't apply to combined therapy or T3 only.
So, low FT3 but high TSH (> 3.0) is still an indicator of poor conversion, but mid to low TSH combined with low FT3 shows good conversion, if I've understood this correctly.
If I can be permitted one last question: what would be considered a low FT3 threshold in the range 3.1-6.8 (i.e the Blue Horizon lab range)?
At a guess I personally would look askance at anything less than 4 for normal converters and poor ones. But that wouldn't necessarily be true for good converters who can get along with lower FT3 because their cells take it in well.
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