T4 - T3

[Mags_23]

Can you tell me if there is a specific test to do that informs you that you are unable or having trouble to convert your T4 into T3

[SeasideSusie Remembering]

Mags - if you test FT4 and FT3 at the same time, you can see if you are converting.

I think the DIO2 gene test tells you something about it but I don't know anything about the test.

[Mags_23 in reply to SeasideSusie]

But how can you tell?? Should one be higher than the other or both the same?

[SeasideSusie Remembering in reply to Mags_23]

If your FT4 is high and FT3 low that means poor conversion.

Good conversion takes place when FT4: FT3 ratio is 4:1 or less.

For example, put very simply

FT4: 21 with FT3: 4 = 21÷4 = ratio is 5.25 : 1 = poor conversion

FT4: 18 with FT3: 5.5 = 18÷5.5 = ratio is 3.27 : 1 = good conversion

[Mags_23]

Thanks for that great info!! It's just so I know how to work it out. If the doc says it's "normal" and as usual it's not!!

[Mags_23]

OMG!!!! Just did my Mum's ratio & it came out at 15.7:1. Yet the doc said her T3 levels where fine!!!!

[helvella Administrator Thyroid UK in reply to Mags_23]

Are you certain that you were using a Free T3 level (and not Total T3)?

Free T3 is (numerically) about three times Total T3. (They are in different units - otherwise that would be bonkers.) Which could account for the ratio you have calculated being so very high.

[SeasideSusie Remembering in reply to Mags_23]

Have you used these results that you posted a couple of months ago

TSH 0.54 (0.35 - 5.00)

Free T4 16.8 (9.0 - 21.0)

Total T3 1.1 (0.9 - 2.5)

If so then it's Total T3 as Helvella has said. It has to be FT3.

[Mags_23 in reply to SeasideSusie]

Aaahhh, I see. Still all very new to this!! Schoolboy error 😕

[helvella Administrator Thyroid UK in reply to Mags_23]

And very easily done.

[jimh111]

You can't use any simple ratio to determine if conversion is good or bad, it's much more complicated. In healthy subjects fT3 tends to increase or at least stay level as fT4 falls. And vice-versa. However, if fT4 goes high type-1 deiodinase takes over and fT3 goes up giving the impression of good conversion but it also produces reverse T3 which blocks the action of T3. So it is difficult to know whether the T3 is 'good' T3 coming from type 2 deiodinase or 'bad' T3 coming from type 2 deiodinase. (It's the same T3 but is it associated with reverse T3?). You could assay reverse T3 but nobody knows how much is normal for given fT3, fT4 levels.

If you develop primary hypothyroidism it is very unlikely you would concurrently develop a deiodinase problem.

I would go by symptoms, response to T3 medication and guided by blood tests. If your fT4 is around 18 or 20 and you still have obvious hypo symptoms then cautiously add in some liothyroine and perhaps reduce the levothyroxine a little. If there are any signs of hyperthyroidism back off.

There's no doubt some patients need T3 medication but it is poor science to claim they are not converting. If you say this to an endocrinologist the better ones will know it's not true and you will be shooting yourself in the foot.

[Mags_23]

Now I'm totally confused!! 😭😭

[jimh111 in reply to Mags_23]

Good! You've grasped the concept that it is too complicated to use a simple test or calculation.

[SeasideSusie Remembering in reply to Mags_23]

Mags_23 I wouldn't worry too much at the moment. The information about conversion and FT4: FT3 ratio comes from member Diogenes who is Dr John Midgely, one of ThyroidUK's advisors. You can read about him on ThyroidUK's main website > About Us > Advisors thyroiduk.org.uk/tuk/About_...

I would get your mum's FT4 and FT3 tested at the same time and take it from there.

[Mags_23 in reply to SeasideSusie]

Thank you for your very helpful & useful information xx

[t3rcam]

I think there is a real risk of not being able to convert T4 to T3 which results in Rt3. Have you had a look at the Rt3-adrenals yahoo group? They seem to have a fair bit of information on this too.

[jimh111 in reply to t3rcam]

rT3 comes from type-1 deiodinase (D1) which converts T4 to T3 and rT3 in equal amounts. D1 increases when fT4 is high, so just keep fT4 within its reference interval and it should be OK. i.e. don't take too much levothyroxine.

Type-2 deiodinase (D2) converts T4 to T3 but does not make rT3. D2 reduces as fT4 increases (and I believe TSH falls). These two mechanisms tend to keep the overall hormone status level and reduces the effects of hypo or hyper thyroidism.

Some patients need T3 medication, there can be various reasons but not because they can't convert, although it is possible they may have reduced D2 activity or a need for supraphysiological T3 levels.

[LAHs]

And here is a different tack: Increase your selenium (Se) intake, either by a supplement or by eating Brazil nuts. If you feel better, then you were not converting. The processes JimH refers to require the catalyst selenium, if you are low in Se, then you will not produce much T3.

Oh, and it is a good idea to get your Se level measured before you supplement - and any other mineral for that matter. Measure first and only supplement if you are low.

[Sealsharp1952]

You can also have your free t3and free t4 tested and TPO good luck 🍀