Thyroid UK
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Is there any point in testing for rT3, fT4,fT3?

Hi - I am currently on 125mg levothyroxine & wonder if I am converting my t4 to t3 correctly. A nutritionalist recommended thyroid antibodies test, rt3, ft4, ft3 etc... but if my doctor is not going to give me NDT or anything other than levothyroxine then what’s the point in having any further tests? I have the usual B12, vit D tests done so I know about them. Thank you

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Not sure about rT3 but the others ,yes.When were they last tested.

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A few years ago but if a doctor only prescribes you Levo for your t4 level then what’s the point in the others? Will I get different medication/dose?

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The point is that if you read posts on this site you know you need to take charge of your health and have the ammo to face the medics.

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Not much point in testing rT3, agreed, but the others are essential and nothing to do with just taking levo.

TSH is not a thyroid hormone, it is a pituitary hormone which stimulates the thyroid to make more hormone, when the pituitary senses that blood levels are low. The lower your thyroid hormones, the higher the TSH rises. When thyroid hormone levels rise, the TSH decreases.

BUT, although that is great in theory, it doesn't always work like that in practice. The TSH is slow to react, so it could look perfect on paper, but the thyroid hormones still be too low. Once you are on thyroid hormone replacement, the TSH ceases to be of much use, unless it goes high, which will mean that you need an increase in dose, but a low TSH has very little significance. The TSH should never be used for dosing purposes.

FT4 is the test that tells you how much T4 you have available for the body to use. T4 - levo - is a storage hormone which, in theory, is converted to the active hormone, T3, as and when it is needed. In healthy people this works very well. In people with thyroid problems, it's more difficult.

FT3 is the test that tells you how much T3 you have available for the body to use. And, it's pretty important to know that, because it's low T3 that causes symptoms - that is what hypothyroidism boils down to : low T3. So, in an ideal world, the main test used for dosing would be the FT3. But, it's the most expensive test, so doctors try to tell us we don't really need it, etc. It's all bluff.

Also, testing the FT3 and the FT4 at the same time, will tell you how well you are able to convert T4 to T3, so that's pretty important to know, as well!

Antibody tests - TPO antibodies and TG antibodies - will tell you if you have Autoimmune Thyroiditis - aka Hashi's. That's pretty important to know, as well. Because, although there is no cure for Hashi's, there are some things that can be done to help control it - things that doctors know nothing about!

Firstly, you need to keep your TSH suppressed, when you have Hashi's, because that limits the Hashi's swings from hypo to 'hyper' and back again - which can be pretty disturbing. You can also adopt a gluten-free diet, which could reduce antibodies, and make you feel better, because antibodies often cause symptoms. And, you could take selenium, which not only reduces antibodies, but also helps with conversion - Hashi's people are often poor converters.

So, yes, there are many points to getting those tests done, even if you're only on levo monotherapy. The sad, rediculous part is, that doctors do not understand any of that because they just don't do it in med school. In med school, they are taught that all they need to do is prescribe levo until the TSH is back in range, and their job is done. Why? Because it's cheaper! :'(

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Oh wow - thank you for all this information - it had been really useful & I will proceed on the information given! How do you know so much?!

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17 years of reading, researching and talking to people. That's the only way to do it.

Glad to have been of help. :)

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I copy good chunks of useful info ( like from the Guru Greygoose) into a word doc - so I can re access for future use when talking with my Doc !! My treatment has only improved because of knowledge from here !

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Greygoose, I believe that you can have tissue hypothyroidism with a decent level of free t3 in your blood. ft3 is an important test, but like everything else, it is a partial picture.

I guess if you look at how bad your conversion is (free t4/free t3 ratio), then you don't need to test for rt3 because you know where your levo went. I don't think the actual rate of conversion varies much, just the ratio of conversion to ft3 or rt3.

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You mean problems absorbing at a cellular level? Well, of course you can, but I wasn't writing a book on the subject, just a brief over-view to help the OP understand the different tests.

You don't need to work out ratios, just looking at the FT4 and FT3 will give you an idea of conversion. If you get hung up on ratios, then you could end up with less T3 than you need. ratios are for healthy people, not hypos.

T4 will start converting to rT3 when unconverted T4 gets too high - i.e. converting to less T3 and more rT3. You don't need an rT3 test to see that.

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True to a large degree on the testing. And too low an ft3 is a problem by itself. But there are those that firmly believe that rt3 competes with ft3 for cellular receptors. So, to a degree it could be about competition, rt3 vs ft3. If that is true, you can have a decent level of serum ft3 and if rt3 is high the serum level is partly due to the idea that ft3 has nowhere to land. So, the ft3/rt3 ratio can be important...but like everything, it isn't the whole picture. So, I don't think the rt3 test and ratio is valueless. It is just part of the picture, as are the rest of the tests.

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It has now been proved that rT3 does not compete with T3 for receptors, rT3 has its own receptors.

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Is there a study you are referring to? I am interested.

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I suggest you have a look through diogenes' responses to questions. I don't think he ever posted a link, but he did talk about it.

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Found it!

healthunlocked.com/thyroidu...

There is a link. :)

Even so, it's most edifying to read through diogenes' responses on all sorts of thyroid subjects. Not just his posts, but also his responses.

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I have read and value many of diogenes' posts. The study he referenced was regarding specialized rt3 receptors in the liver. Whereas the liver has a large role in conversion, it would not be unreasonable to wonder if the rt3 receptor sites could be unique to that tissue, as it functions differently. In any event, I do believe that he acknowledges that rt3 likely does have biochemical effects on the cell, regardless of how it happens. Based on the liver study and opinions regarding it, I am not ready to believe that rt3 is simply a neutral pathway to dumping excess t4. There are so many opinions and so much unknown, I don't think any of us can afford to be dogmatic regarding rt3 at this point.

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But, one has no proof that it is in any way a problem, either.

Of course, it's not just a dumping ground for excess T4, high rT3 can be caused by a lot of other things, too. And, I did say that it was an indicator of some sort of problems somewhere, not just excess unconverted T4.

But, if you have a blood test, and find that you have high rT3, what exactly are you going to do about it? The majority of doctors have never even heard of rT3, so no point in going to see one of them. If you have excess unconverted T4 in your system causing high rT3, the ideal thing to do is lower your levo and add in some T3, but that's not always easy, is it. And, what if doing that doesn't lower your rT3? What then? I can't see any point in looking for problems if you don't have any solutions to them.

I presume you read the bit where diogenes says that rT3 only lasts one hour in the blood. Hardly a long-term problem, then, is it? And, even if it does compete with T3 for cell receptors, it's not going to compete for long before it's converted into T2. So, how much of a problem is that? I honestly think that rT3 is a bit of a red herring, hyped up into a whale, by certain other sites that shall be nameless.

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I can only tell what my own experience has been. ft3/rt3 ratio of 13 when on levo/cytomel 100/10. Switched to NDT 2 gr and ft3/rt3 ratio went to 24. ft4 well below range. ft3 rock bottom of range. And I feel so much better. So, I have reason to believe that there may be something to it.

I agree that rt3 clears quickly, but if you have a conversion problem, you are always making more. So the effects could be constant.

I have read many of your posts and you seem very reasonable. Please consider that the jury is till out...

And I agree, treatment, ahem, should I say self-treatment, would consist of addressing any reasons for poor conversion and then lowering t4 and raising t3. At least that part seems simple, lol.

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Well, of course I consider that the jury is still out. It's still out on a whole lot of things, and we have to be constantly shifting our ideas as we learn new things.

But, there's no point in getting people all worried about rT3 when you don't have a solution for the them. I prefer to tell them to concentrate on their FT3, rather than fixating on the rT3.

You have to remember and consider your audience, when you post on here, and try not to confuse people with too much information, too soon. Someone comes on here, knowing nothing about thyroid - or, at least, we don't know how much she knows - and a head full of brain-fog, there's only just so much information she can absorb. In the beginning we have to keep it simple. The more complicated issues - like rT3 - can be discussed at a later date. That's only common sense, don't you think? One step at a time, that's my motto. Answering this question, it just needed a simple narrowing down of which tests where the most important tests at this point, to this particular person. It didn't require a philosophical debate on the subject of my short-comings as a responder.

And, now, I think we've hogged this poor lady's post for long enough. Remember, she gets notification every time someone posts on her thread, and I very much doubt that any of this discussion is of interest to her. Thank you.

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Knowledge is power. She can read what she wants to or not.

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WOW !!!! greygoose I'm hiring you as my TOP RATED #1 DR . No Dr ever takes the time out to explain as eloquently as you do greygoose . It's because they just DON'T KNOW ANYTHING ABOUT OUR THYROIDS AND HOW TO TREAT US AND OUR THYROIDS RIGHT . Thank You for sharing your knowledge with us .

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You're welcome. :)

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As a general rule if I have these tests done where should I roughly be in the range (for example I know with TSH it should be 1.0 or less). I will either go to my doctor to get these tests or medicheck but just wondering about where I should be in the range levels? Tks

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Well, it's really more about how you feel than where you are in the range. Yes, the TSH should be 1 or under, but we only say that because that's where most people find they feel best. The Frees should be at least over mid-range, but after that, it's a very individual thing, because we're all different. And, if you still don't feel well, then the level isn't high enough for you.

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Brilliant - thanks for your reply

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You're welcome. :)

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This is the one lots of people (including me) use:

medichecks.com/thyroid-func...

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