Does rT3 always have to be bottom-range in orde... - Thyroid UK

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Does rT3 always have to be bottom-range in order not to have an rT3 problem?


My rT3 result from 2 months ago was 143 (90-215) so at the 40% of the range. I was feeling very hypo.

Did I have a rT3 problem back then? My rT3/FT3 ratio was over 20, like 26.

39 Replies

I don't believe rT3 assays are useful. They measure total rT3 so how can it be compared to free T3? Also as far as I know nobody knows the relative binding affinity of thyroid hormone receptors to T3 and rT3, or how effectively they are transported into the cells. I'd just keep fT4 within its reference interval and not bother measuring rT3.

Thank you, jimh111.

Is your FT4 below mid-range?

No because I am on mainly L-T3. From the rT3 point of view if you keep your fT4 below the upper limit of its reference range you should be OK. This is because as fT4 goes high type-1 deiodinase (D1) takes over and D1 produces equal amounts of T3 and rT3. I feel rT3 assays are a waste of money. You will get high rT3 if your fT4 is high.

Thank you again! That is a really interesting point of view. I will take it into consideration. So far I have encountered opinions supporting the mainstream point of view regarding rT3.

Do you keep your FT4 within range while mainly on T3 only?

No my fT4 is rather low but I'm an unusual case.

I think I am an unusual case myself since I cannot get better no matter what I try...

You said you were on T3 mainly. But do you take any T4 whatsoever?

The L-T4 doesn't make much difference but I take 50 mcg as it helps me reduce my L-T3 by 10 mcg and there's just a chance that L-T4 has beneficial effects we are not aware of.

How much T3 do you take, do you multi-dose. I seem to not be able to tolerate T3 when I have no T4 in my system.

Also I have not had my cortisol tested.

But it is most convenient for me to take T3 in the middle of the night, long before waking up in the morning, at least 2 hours before that. I take my T3 at once.

Since I have not had a saliva cortisol test yet and I don't know whether my morning cortisol is high or low I am afraid to take T3 in the middle of the night because if my cortisol is normal or high it might get further raised by the night/early morning T3 dose.

Do you think it is dangerous to take T3 in such a way given that I don't know my morning cortisol number?

It really is convenient for me to take my drugs this way. I have always done so with T4.

It's best to take T3 medications in divided doses, to obtain stable levels. Three times a day is ideal but twice is OK (the levels vary but the effects don't, receptors take hours to respond to T3 saturation). I take L-T3 twice daily, before breakfast and at bedtime. The bedtime dose is more important, it helps with deep restorative sleep. If it stops you getting to sleep you are on too high a dose.

Cortisol is irrelevant. There are rare cases of impaired adrenal function in patients with longstanding severe hypothyroidism, these patients can't tolerate small doses of thyroid hormone but they recover in time. If cortisol (too much or too little) was affecting thyroid hormone action then the TSH would not respond to thyroid hormone, it would stay high. I don't see any point in carrying out cortisol tests in most patients.

I notice that you have a large number of posts, too many for me to read! So, I'm not sure what you are taking and what your symptoms are.

Thank you, Jimh111!

It is another interesting point of view you offer here.

I became hypothyroid roughly 2 years ago, 1 year after the birth of my first child. I have been on T4 since I fell pregnant a year ago and I was doing fine on T4 with 1-2 bumpy occurrences when I had to stop T4 for a week, let FT4 level fall down, TSH go up, and then restart T4. And this worked, I don't know why, but it worked and I would get euthyroid again on only 42 mcg T4, I was symptom-free.

Since I gave birth 7 month ago I have been struggling to make the same restarts with T4 but it just would not work. I tried, but FT4 does not fall down so much as in pregnancy, instead when restarting T4, FT4 level goes high and FT3 stays low.

Then I decided to try T3. I tried small doses of T3 along with 25 mcg T4 and I felt extremely ill. I did not know what was going on. I was becoming very hypothyroid.

Then I decided to go T3 only. I noticed I cannot tolerate small doses of T3 if I don't have T4 in my system but apparently T4 is blocking my receptors along with rT3 or at least that was the assumption I was acting upon. So going T3 only was a disaster, it was a mixture of hypothyroid and hyperthyroid symptoms at the same time. Then I decided that I must have a major adrenal problem...

Then I decided to give T4 another chance. Starting T4 for a second time was like I was in heaven, I felt so good at the beginning, but after a week the positive effects wore off and I became hypothyroid again.

I bumped my T4 to 188 mcg, every time I bumped my T4 dose, I felt asymptomatic for a week and then deepening hypothyroid symptoms reappeared...

I am lowering my T4 now, and trying to go T3 only, but am afraid since I really cannot tolerate small doses of T3. I am afraid I will never feel normal again.

If I take T3 in the middle of the night it is OK, I have no adverse effects.

But I have read it on the Recovering with T3 website that if one has normal or high morning cortisol one should not take T3 in the 4-hour cortisol production window because it will raise cortisol too much.

Initially I thought I cannot have a major adrenal problem since I have become hypothyroid not long ago... But everybody is telling me: "Test cortisol, get the appropriate nutrients, get everything corrected, get everything right!" and I feel like a wreck already and doomed to never get well since I know that I cannot have all things perfect at the same time for thyroid replacement to work. (Besides during my pregnancy I became iron deficient and thyroid therapy was still working beautifully.)

Also on another forum everyone suggests I have a high rT3 level blocking the cells' receptors. That is why I am going T3 only now... I doubt it it will work though. Last time on T3 only was a living hell.

My symptoms are:

skipped beats - thousands a day, which disappear at a good FT3 level, that is the main symptom I go by, and it is the first to appear and the last to disappear when on thyroid treatment.


Bone and muscle pain

Brittle nails and hair

This is a little too complicated for me! In general I'm not bothered about rT3, it will sort itself out if you don't let fT4 get too high. I feel cortisol is much overstated, impaired adrenals are quite rare. The missed beats are a concern. I believe you have seen a cardiologist and they haven't found anything. Although T3/T4 may be helping it may be acting as a therapeutic agent. That is your missed beats are not due to insufficient thyroid hormone in heart but that the T3/T4 is overcoming the missed beat problem. This is not good, because too much T3 in the heart can lead to atrial fibrillation in the long run and this increases the risk of stroke. If you take T3 medication I would split it into two doses so as to even out your dose. When having a blood test have the blood taken roughly five or six hours after your last T3 medication so that you get a reasonably accurate result.

I would suggest you supplement with magnesium citrate. Magnesium is important for cardiac function. Magnesium blood tests are no use, they don't reflect tissue levels, the best test is a trial of supplementation. Low magnesium also causes stress. So low magnesium could affect your heart directly and indirectly by an increased stress response. Magnesium supplementation sometimes corrects heart conditions such as mitral valve prolapse, it is a very safe option and so worth a try.

Jimh111, the skipped beats are just a symptom of hypothyroidism, they are due to insufficient thyroid hormone. They have nothing to do with magnesium. When I am euthyroid I have zero skipped beats. Whenever my FT3 falls, my heart rate slows down and I immediately start experiencing skipped beats (up to 20000 a day). It is just a symptom of low thyroid function. There is nothing wrong with my heart. When I am properly medicated I have no skipped beats.

I had never had skipped beats before I developed full-blown Hashimoto's and hypothyroidism.

I supplement with magnesium nevertheless but it makes no difference and has never had. Only proper thyroid function resolves my symptoms, one of which are my skipped beats.

People here are telling me that my rT3 should have been about 100 at most instead of 143 in order for me not to have a problem (90-215 - reference range). So it should be at the low end of range. Mine was 143.

I have been taking 188 T4 since then thinking that I don't have a rT3 problem so my rT3 should have gone up.

Aren't the reference ranges for rT3 based on unhealthy population's results meaning that actually the upper reference range should be much lower? And that rT3 must be much lower in general? And that a rT3 result falling within range does not mean that one does not have a rT3 dominance?

I cannot get my head around this issue with rT3. Some people say it matters, others say it does not.

My FT3 is over range now, but I still feel pretty bad (overwhelming fatigue, brain fog, severe muscle and bone pain, and skipped beats), so there must be something interfering with FT3 action in the cells... and only rT3 comes to mind...

I too think that impaired adrenal function is quite rare with hypothyroidism but why does almost everyone with hypothyroidism I know have either low or high cortisol reading on their saliva corisol test?

I cannot get my head around this either.

rT3 will come down if your fT4 is not too high. Nobody, I mean nobody, knows how to make sense of an rT3 figure. It measures TOTAL rT3 and it doesn't make sense to compare it with FREE T3. Nobody knows how much rT3 is transported into the cells compared with fT3 and how strong its affinity for thyroid hormone receptors is compared to T3. I'm not surprised you can't make sense of it, there is nobody in the world who can, the research isn't there. Supplementing with magnesium (which form?) has ruled that out. If you take large doses of L-T4 which push your fT4 high then it becomes ineffective. We know this happens from experience and it is probably due to rT3. That's all that is known.

What do you mean by "FT4 too high" - over range FT4, or just high FT4 but within range?

Even on high T4 doses my FT4 never went over range.

Yes, taking more than 150 T4 became ineffective for me. Maybe I have a high rT3 now?

Why does my FT3 is over range now and it is ineffective? I feel very hypothyroid.

Can rT3 (from taking high doses of T4) block my receptors (although this cannot be proven)?

Why do some people cannot take T4?

Why is there such a term as "pooling" of FT3?

Isn't rT3 the culprit for everything?

Why do you take mainly T3?

Why do people still take rT3/FT3 ratio into consideration when it comes to ineffective thyroid treatment?

The blood rT3 test does indeed measure only total rT3. Why don't we get a new ratio then - between TT3 and Total rT3?

Why do many report great alleviation of hypo symptoms when (possible) clearing rT3 happens?

Doesn't taking T3 drive T4 to convert to more rT3 then?

Please, don't think I am arguing with you by asking all this questions. I just want to get better and get a good grasp of thyroid stuff. I've been into it for 2-3 months only, so everything is fairly new to me.

I am supplementing with magnesium citrate. My skipped beats are just a symptom of low thyroid, indeed.

Just a general response. I don't know at which fT4 figure rT3 is increased. High fT4 induces type 1 deiodinase which produces T3 and rT3. I'm guessing but I would have thought an fT4 below 20 is fine, just judging from my own experience. rT3 does block T3 receptors, as far as is known, but the effect hasn't been quantified. The more rT3 the worse, that's what's assumed. People take rT3/fT3 into account because some doctors say so (I think it's false science) and because the companies that sell the rT3 test mention it. fT3 is the relevant number, using TT3/rT3 would be even less precise. High levels of fT3 will increase rT3 production but the fT3 wins the race. This is a mechanism to prevent hyperthyroidism but it doesn't have total control.

Thank you!

And what is your own experience? Why do you take T3 mainly? Do you suppose you had a high rT3 level?

Maybe I am feeling very hypo with an over-range FT3 because something is really blocking the receptors. At least I cannot come up with another explanation...

Otherwise I might need supra-physiological levels of FT3 to feel well since my thyroid is not healthy anymore and may require different levels of FT3. And I don't really know what my levels were when I was healthy, years before I developed thyroid disease.

High levels of FT3 will increase rT3 production only in the presence of exogenous T4, right? Otherwise rT3 has nowhere to come from, no T4, no deiodination.

Do you think I might have thyroid hormone resistance? With this over-range FT3?

But I cannot tolerate T3 much.

I had severe hypothyroidism with perfectly normal thyroid hormone levels. I needed supraphysiological doses of thyroid hormone to recover. I assume I need T3 because when you take supraphysiological doses of levothyroxine the deiodinases reduce T4 to T3 conversion and produce more rT3. I have a form of resistance to thyroid hormone that I believe is caused by endocrine disruption. The substances that cause this have very long half-lives. So in your case this would not apply as you had an elevated TSH and more importantly your symptoms have progressed too quickly.

You are correct in saying high fT3 levels will only lead to rT3 if there is T4. I forgot this apologies. This situation would only occur in cases of hyperthyroidism where there is high T3 and T4 output. If someone is taking high doses of T3 throid output will fall and there will be little T4.

I'm not sure what you mean by 'you can't tolerate T3' what symptoms do you get? And how much T3?

I still think you have a cardiac problem or it is stress related (a friend of mine had this). It just seems strange that you initially responded to a little levothyroxine and now require much more hormone. I've no expertise in this area so I could be completely wrong! If I were you I would titrate my thyroid hormone according to hypo / hyper signs and symptoms without factoring in the heart problems.

No, Jimh111, I don't have a cardiac problem, that is for sure. It is just my hypo levels messing up with my heart, giving irregular heartbeat.

I really don't know why I was fine with so little T4 before.

And I am really not stressed. I know my body very well.

When I gave birth 7 months ago my thyroid function restored for a month (that is what happens to all women who give birth - thyroid speeds up its function). I had not had a single hypo symptom for a whole month -including the skipped beats. I had none.

When I have little T4 in my system, T3 gives me an elevated heart rate, jitters, and a headache, and my hypo symptoms (fatigue and muscle and bone pain) increase since there is not enough T3 to alleviate them). This happens even from a 10 mcg T3, or even less. The less hypo I am (i.e. the more T4 I have in my system), the bigger doses T3 I tolerate, with almost no adverse symptoms.

My levels now are normal and I still feel bad:

TSH 0.005

FT4 14.92 (9.3-17)

Ft3 4.47 (2-4.40)

I have Hashimoto's.

I think T3 pools in my blood not reaching the cells.

I suspect you can tolerate more T3 when you have good T4 levels because the body can protect itself by producing rT3. Your levels are not normal because your TSH is suppressed and your fT3 high. If you take L-T3 once daily and the blood was taken > 10 hours from your last dose your fT3 result will be inaccurate. On the other hand if you left < 8 hours the result will be inaccurate the other way.

The heart will respond rapidly to thyroid hormone, particularly T3. Fatigue and muscle and bone pain will respond more slowly. I've found that L-T3 helps with getting good deep sleep and this reduces fatigue and muscular aches (we produce growth hormone in stage 4 sleep and this repairs muscle 'microtrauma' that naturally occurs during the day). If my fT3 is too high it takes some time to fall asleep.

I don't like the term 'T3 pooling in the blood, not entering the cells' as it is scientific nonsense. The T3 is clearly entering the cells because it enters the pituitary cells and suppresses your TSH. It is possible that T3 is not binding to receptors in peripheral tissues but I don't see how this could come on over what is a relatively short period. This is an academic point but if we accept the T3 pooling nonsense the danger is that we then design a treatment based on a false premise and get things wrong. It's good enough to say you have high fT3 levels but you don't seem to respond to it. Unfortunately some alternative doctors put forward theories like T3 pooling without there being any evidence to support it.

So, what is my alternative? Slow-release T3?

I cannot tolerate T3 but it may turn out to be my alternative. I cannot get better with T4 only and with T4+T3.

I am afraid to try NDT and T3 because of a rT3 problem.

The pituitary tissues do not have a deiodinase necessary for the conversion of T4 to rT3. Maybe that is why TSH is so sensitive to a small amount of T4 and T3.

It seems to me that at one and the same T3 dose certain cells of certain organs in our body can be hypothyroid while others requiring less amount of T3 to saturate them, can be fine, euthyroid.

My blood was taken 21 hours after a T3 dose.

Interestingly enough, most people report tolerating T3 much more after the so-called T4 and/or rT3 clearance.

I seem to be the opposite.

Type 1 deidinase is primarily in the liver, so rT3 is in the blood and picked up by the pituitary, heart, brain etc. I'm sure there can be different tissue responses to thyroid hormones. After 21 hours your TSH and fT3 figures will underestimate your average levels. I'm not sure you have a substantial thyroid problem, but I've no idea what the problem is.

I do have Hashimoto's for sure and a failing thyroid and a bunch of thyroid-induced symptoms.

I may have developed some sort of resistance.

Or something may have become "broken" at a cellular level, or at receptors' levels.

Or I may have just developed a high rT3 problem.

My rT3 stands at 40% of the reference range while it must be lower and that result was only after 2 months on relatively low doses of T4.

Now my rT3 must have popped at 60-70% of the reference range at least as I have been taking higher doses of T4 since.

130396 in reply to jimh111

Does this apply if you’re on combo T4 and T3?

I mean is rt3 not relative ?



When I was looking into this, it said the ratio should be greater than 20

I know, SeasideSusie.

My ratio was 29 but I still was very hypothyroid. My FT3 is high but I still feel ill. I might be pooling. Oh...

Jimh111 might turn out right about rT3.

Sometimes the conclusions on STTM site seem slightly dogmatic to me.

SeasideSusieAdministrator in reply to YulianaRossenova

I don't particularly like that site, just that they had the information about ratio.

I recently had rT3 tested with Blue Horizon and the range was 10-24. (This was because I'd had just about everything else tested and I wanted to see if there was something I was missing.)

I totally commiserate. I am doing the same... Testing everything possible to check out for possible problems that may require correcting. I don't even get slightly better with T4, T4/T3, or T3, so I really don't know what to do.

What was your rT3 level?

SeasideSusieAdministrator in reply to YulianaRossenova

My rT3 result was 22 (10-24)

rT3 ratio is 27.9

I should have done it months ago, before introducing T3, but couldn't get a blood draw done.

Thank you!

And how were you feeling at that time?

How are you feeling now? What T4 and T3 dose are you on?

SeasideSusieAdministrator in reply to YulianaRossenova

It's hard to say how I'm feeling, there is a lot going on.

I tested adrenals - apparent 'low adrenal reserve' (practioner diagnosis) with top of range cortisol for first three readings, mid range for last one. DHEA were right at the bottom/under range.

Sex hormones - rock bottom for all (I am post menopause).

I tested negative for candida, middle of range for iodine, B12 top of range, folate very near bottom of range, Vit D severely deficient, ferritin 35.

I was on 175mcg Levo.

TSH suppressed (always has been), FT4 over range at 29 (12-22) but had been top of or over range for years, FT3 about half way through range at 5 (3.1-6.8) and had never been higher.

Urine thyroid test showed T4 39% through range, T3 minus 6% through range so confirmed what I though about conversion not good, nothing much getting through to the cells . That's when I started to add T3 to my Levo.

I was feeling dreadful at the time at the time those tests were done. I should have had rT3 done at that time but couldn't get a blood draw.

Adaptogenic herbs and bioidentical progesterone cream recommended for adrenals/sex hormones by practioner. Melatonin for sleep after 5HTP did nothing to help. I still use all of them.

Vitamins and minerals are all now optimal and am still supplementing to keep them there.

On 100mcg Levo and 25mcg T3 my FT4 was 18.6 (12-22) and FT3 was 6.14 (3.1-6.8)

Current thyroid meds are 100mcg Levo and 31.25mcg T3. Still testing and tweaking, next test due end of this month.

I'm better than I was, not perfect though. Still fatigue, poor sleep, it's a good job I am retired!

I don't know if I had high rT3 and adding T3 and reducing Levo has reduced it. I think that might be the case but have no proof. I certainly feel better than on Levo alone but despair of ever getting to the bottom of it completely and ever being properly well. But I also have a lung disease and regular flare ups of a colonised lung infection, none of which helps as that can make me feel unwell too.

Wow, thank you for your thorough reply!

Did you have some symptoms corresponding to the top range cortisol for the first three readings and the mid-range for the last one? Inability to fall asleep?

I cannot get urine thyroid test done here.

But I can feel almost nothing of what I take reaches my cells.

You had been on Levo only for how many years?

SeasideSusieAdministrator in reply to YulianaRossenova

I really can't say what symptoms could be attributed to what. I didn't feel anything in particular that I could say was definitely, say, severely deficient in Vit D for example, or low DHEA, or top of range cortisol.

Poor sleep has been a problem forever. Two hours plus to get off to sleep, mind not shutting down, always thinking of something and 'mind chattering'. Difficulty getting up because of unrefreshed sleep, even now.

I'm not a particularly stressy person, fairly laid back, it is what it is, you can't change what has happened so move on type of person.

I had been on Levo only since originally diagnosed in approx 1975 until end of 2015, so about 40 years. None of my GPs over that time have discussed anything with me.

I saw an endo in 2002 who didn't like my suppressed TSH so he reduced my Levo so low that my FT3 was 2.8 (2.8-7.1), FT4 15.6 (11.8-24.6) and TSH still only 0.4 (0.27-4.2). He was happy my TSH was at last in range so I was apparently well. Trouble is I was actually a zombie. My GP overrode him and increased my Levo back up, which immediately gave me a suppressed TSH and over range FT4 but she accepted that but no further investigation, again I was apparently well!

So I think it's been a case of poor conversion for at least as long as I've been keeping a spreadsheet of my results, 20 years, but I didn't have FT3 tested until 2000.

Gosh, SeasideSusie, that is a long time of living with hypothyroidism...

I have been unwell for 6 months now and sometimes I wish I was dead... cannot imagine living like this for 20+ years.

SeasideSusieAdministrator in reply to YulianaRossenova

Apparently, I know now but didn't at the time, I was diagnosed when Levo was fairly newish in the UK. I think a form of NDT was being used up until the late 60s/early 70s. Not sure if that was a good thing or not - to not have NDT, just given Levo, or to be started on NDT and then have it taken away.

I was OKish on Levo for 20 years though, just this last 20 have been cruddy.

20 years is still so long a time. I can hardly live through 20 months of hypothyroidism. Maybe my symptoms are too adverse, I don't know...


I am so clueless about RT3 levels but was told recently these were high at the upper end of the range for me. It can occasionally indicate something else going on in the body beyond the thyroid. As is rises to basically protect us. Have you ever had C reactive protein and folate tested? Just if these are raised together that can be a marker for something else going on in the body also. Mine were both raised and suspect it's coming from damage to my hip as I get pain from it. I am also pregnant so going to wait until after the birth then get that hip checked out. I was born with dislocated hips and the past 4 years one in particular has been hurting lots.

YulianaRossenova in reply to Hidden

Yes, Katiekatie, CRP was fine, and folate was little short of mid-range. I have been supplementing with little folate ever since.

Basically, rT3 is formed via deiodination from T4.

Hidden in reply to YulianaRossenova

So it's not that then for you. It would most likely be raised a lot more though anyhow. Weird thing is my folate was high despite having stopped supplementing it 6 months earlier.

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