How useful is a reverse T3 test in diagnosing HYPOTHYROIDISM?

There has been frequent questions recently on Reverse T3.

For information regardng Reverse T3 cursor down to No.4 to read the statement, which is in simple terms. An extract:-

Old studies show that on average, most people convert more than 50% of their T4 to reverse T3; correspondingly, they convert less than 50% of T4 to the metabolically active hormone T3. And the levels of reverse T3 fluctuate up and down through the day. Because of this, I’m never confident of coming to a conclusion that someone has a problem with high reverse T3, not unless the person has had multiple measures of the reverse T3 over a 24-hour period.

Like the TSH, free T4, free T3, reverse T3 levels vary dramatically every 30 minutes or so. Depending on when a person’s blood is drawn or saliva taken. Sometimes the levels will vary enough so that a clinician will give the patient a different diagnosis from the one that he or she would have given 30-minutes before or after the blood or saliva sample was taken.

So blood levels vary rapidly. Because of this, I don’t believe the reverse T3 or the other lab tests in general are very useful. However, I do believe the reverse T3 is useful under one circumstance: when we have enough measures to get averages over time, and when the levels are regularly way out of range. So, in my view, the reverse T3 can be useful, but I think its usefulness is limited, which is true of the TSH and other thyroid hormone levels. >>>

toopoopedtoparticipate.com/...

26 Replies

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  • Excerpt from the prestigious Mayo Clinic:

    Clinical Information

    Reverse triiodothyronine (rT3) differs from triiodothyronine (T3) in the positions of the iodine atoms attached to the aromatic rings. The majority of rT3 found in the circulation is formed by peripheral deiodination (removal of an iodine atom) of T4 (thyroxine). rT3 is believed to be metabolically inactive.

    The rT3 level tends to follow the T4 level: low in hypothyroidism and high in hyperthyroidism. Additionally, increased levels of rT3 have been observed in starvation, anorexia nervosa, severe trauma and hemorrhagic shock, hepatic dysfunction, postoperative states, severe infection, and in burn patients (ie, "sick euthyroid" syndrome). This appears to be the result of a switchover in deiodination functions with the conversion of T4 to rT3 being favored over the production of T3.

  • Reverse T3 is produced by type-1 and type-3 deiodinase both of which increase with high thyroid hormone levels. So as far as I can see the rT3 assay doesn't tell you anything other than perhaps you are taking lots of levothyroxine.

    If I remember correctly there are some obscure disorders where rT3 is high or low but in each case there were more obvious signs. It isn't worth spending money on an expensive blood test that doctors will ignore and nobody knows how to interpret.

    This post reminds me how much we miss John Lowe.

  • He is certainly a huge loss and I knew a little about his background but not as much as I read yesterday and his struggle to learn as a young boy in school and how he scraped through. It wasn't until he discovered Thyroid Hormone Resistance that everything righted in him as regards mental function. So it seems to me he found his path to help people struggling with health issues.

    It also made me wonder if children diagnosed with various difficulties at school i.e. ADD etc have ever had full thyroid function tests and notice taken of them.

  • I must admit, I've been concerned by the number of fairly newly-diagnosed hypothyroid folk posting here lately about RT3 and panicking over taking levo. It's not the first thing anyone should worry about - only after everything else has been ruled out, e.g., that they're on sufficient thyroid hormone replacement, that there are no nutritional deficiencies, no co-existing conditions like gluten sensitivity or PA etc.

    Maybe it's just me, but it worries me when people only just prescribed with levo immediately start asking where to buy NDT and T3 because they're "certain they must have high RT3".

    Not sure how that's come about - maybe because Blue Horizon now offer the test? - but it's a worrying trend.

  • Agree Jazzw :-)

  • I agree that it appears to be a 'trend' and if people are so unwell they will get a blood test and may spend money they can barely afford. They don't realise that T4 converts to RT3 anyway (just read that from Dr L)

  • If only these issues could be investigated by thorough research :(

    I may be wrong, but I believe my poor ratio of rT3 to FT3 of 11.28 indicated why I felt under par, with a FT4 of 19.59 (12-22) and a FT3 of 4.33 (3.1 - 6.8). This was on a dose of 75mcg of Levo only.

    I have one faulty DIO2 gene which means I don't convert T4 to T3 very efficiently and am aware of suggestions that excess FT4 will convert to rT3. It makes sense to me.

    6 weeks on from those tests and built up to a combined (2 x daily split) dose of Liothyronine at 12.5mcg with 50mcg Levothryoxine results came back as FT4 12.81 (12 - 22) and FT3 4.13 (3.1 - 6.8).

    Accordingly, I am increasing my T3 dose gradually as I am guessing that FT4 is less use to me although I am still on 50mcg. I wonder what my next 6 week test will show and I wish I could afford the luxury of having the rT3 checked again.

  • The DIO2 polymorphism has very little effect, the research only just detected minor cognitive impairments with the polymorphism in both genes. Our thyroids produce about 6 mcg T3 daily. As you are on 12.5 mcg you already have double the amount of supplementary T3 that your thyroid would have produced in its prime. The rT3 to fT3 ratio compares total rT3 with the free fraction of T3. Consequently, I can't see how it is of any use. rT3 will be high if fT4 is high. This ratio will definitely be lower if one is taking T3 medication, an rT3 assay would just confirm the obvious. By paying for another rT3 you would just be confirming the assay works as expected.

    I don't mean to pick on you, just try to bring out some of the points raised by the research. The DIO2 and rT3 assays are of little scientific use for patient care and consequently from that viewpoint a waste of money. However, they do often enable doctors to rationlise prescribing T3 to the benefit of patients albeit for the wrong reasons!

    I wouldn't worry too much about the blood test results as long as the figures are not too dramatic. Your very first post on this forum said that you were fine until the doctor dropped your levothyroxine dose in response to a blood test!

  • @jimh111 - I have cognitive impairment aplenty! Even been to my GP re possible dementia diagnosis, but he didn't take it seriously - no surprise there.

    My first post saying I was fine didn't take into account that although Levo initially helped with symptoms, I was still falling asleep in the evening, unable to stay awake to a reasonable bed time, never lost any weight, despite ridiculously healthy lifestyle, had constant broken nails, constipation, often being emotional and fluctuating depression, etc. I had just got used to these things. My pulse and blood pressure have always been low and also my temperature.

    Through research on this forum I realised I was not optimal - though still not optimal - I feel much better now. Since being on T3, I have had family trauma, gone through a particularly difficult redundancy process, yet I have managed to keep fairly buoyant. Other bodily functions are improving. I am far from hyper. Pulse rate still too low, temperature still too low, etc. etc.

    The link to my first post is here:

    healthunlocked.com/thyroidu...

    extract "I said I had checked the list of Hypothyroid symptoms on the NHS Choices website and was still suffering ALL of them except muscle cramps and period problems as I am post-menopausal, plus having a constantly low temperature 35-36c, insomnia and high cholesterol (both HDL and LDL high). My eyes are puffy above and below and I have lost the outer third of my eyebrows." Although I said I was feeling fine this is relative, these symptoms did not appear overnight.

    My feeling is that having a DIO2 gene has a cumulative effect over one's lifetime and when you realise that your blood results are not right, the picture of all those things that have impacted on your life become clear. I have had infertility, miscarriage, premature baby, been overweight since childhood (brother and sister slim) always felt tired in the evenings (hubby has always got the tea for us as I feel like a slug in the evening), never been able to remember names of celebrities, places we've been on holiday, always joked with hubby re him being in a t-shirt and me cold and wrapped up, etc etc. the list goes on with labrynthitis, RSI, high cholesterol, etc.

    Sorry, didn't mean to rant, but need answers and feel as though I have one, but harder to have this challenged on here than deaf ears of GPs - no offence intended or meant.

  • We are entitled to rage when we aren't improving.

    The quotes I make are usually by a doctor/scientist/logicial analyst who was also an Adviser to Thyroiduk.org.uk before his early death.

    You can find a lot of good, clear, easy to understand info on the link below (although some topics/links within a link may not be accessed now) on this link:.

    He only diagnosed by blood tests initially and then concentrated thereon on how the patient was progressing. One thing he was adamant about would never prescribe levothyroxine.

    Excerpt:

    Dr. John C. Lowe is a fibromyalgia, thyroid, and metabolism researcher. As Director of Research for the Fibromyalgia Research Foundation, he has spearheaded the scientific study of two related topics: the metabolic causes of fibromyalgia, and the relief of fibromyalgia symptoms through the treatment approach he developed and named "metabolic rehabilitation."

    This is his take on RT3/RT4 - he thoroughly researched T3 when he was a young man and used it only for patients who were thyroid hormone resistant:-

    "Old studies show that on average, most people convert more than 50% of their T4 to reverse T3; correspondingly, they convert less than 50% of T4 to the metabolically active hormone T3. And the levels of reverse T3 fluctuate up and down through the day. Because of this, I’m never confident of coming to a conclusion that someone has a problem with high reverse T3, not unless the person has had multiple measures of the reverse T3 over a 24-hour period. Like the TSH, free T4, free T3, reverse T3 levels vary dramatically every 30 minutes or so. Depending on when a person’s blood is drawn or saliva taken. Sometimes the levels will vary enough so that a clinician will give the patient a different diagnosis from the one that he or she would have given 30-minutes before or after the blood or saliva sample was taken.

    So blood levels vary rapidly. Because of this, I don’t believe the reverse T3 or the other lab tests in general are very useful. However, I do believe the reverse T3 is useful under one circumstance: when we have enough measures to get averages over time, and when the levels are regularly way out of range. So, in my view, the reverse T3 can be useful, but I think its usefulness is limited, which is true of the TSH and other thyroid hormone levels. >>>

    web.archive.org/web/2010103...

  • Thanks Shaws - will check out the link :)

  • You have had a very rough journey right enough and I am sorry. When we don't improve on the thyroid hormones given by the medical profession, that's when we think something must be wrong.

    I was far worse on levothyroxine (which surprised me) as it didn't enter my head that a prescription wouldn't benefit me until I eventually stopped levo. It was an horrendous time and you have my full sympathy and I hope you will get to a plateau in which you will improve but we do need co-operative doctors or, like many on here, forced to source their own which is not right. Or searching for what could possibly be preventing us improving.

  • I agree we need co-operative GPs and Endos. They need to be more knowledgeable and collaborative and to work with us - they just need to be interested in what's best for us, not numbers on a chart.

    I am sorry you have suffered too, but hopefully feeling better now. I am feeling better than I have for a long time, so hopeful that I can keep improving as not all symptoms dealt with yet, but knowing that blood tests showing me under-medicated.

    I know I am no expert, but feel that I know more than my GP and know that they don't have the time or the interest to research. My own self-interest has driven me to learn a lot and it is still trial and error, but I can only use what I have learnt and give it a go.

    Take care and thank you for your sympathetic reply :)

  • There's a comprehensive discussion of rT3 here that anyone attempting T3-only should read first: tiredthyroid.com/rt3.html

    Here's an excerpt (there's a link discussing each point on the site):

    The T3-only protocol is not for everyone, and some people have had serious side effects. Inability to think and remember anything (dementia), severe hair loss, muscle wasting, bone loss (osteoporosis), and high blood sugar (diabetes) are just a few of the side effects.

    Yet other patients claim this protocol gave them their lives back. How is that possible? Different biochemistries require different proportions of T3 and T4.

    Estradiol and SHBG rise to unnatural levels on the T3-only protocol.

    Who made this up? Are they benefiting financially? The cost of compounded T3 far exceeds the cost of generic T4 or desiccated thyroid. The reverse T3 ratio is a nonsensical number because it can be low for several different reasons, each requiring a different treatment.

    Does reverse T3 have a purpose? Yes it does!

    Reverse T3 is made under certain medical conditions by the D3 deiodinase enzyme.

    T4 is used by many cells in the body, especially hair; it is more than a prohormone and there are indeed T4 receptors.

    The brain needs ample T4 to function properly and high levels of T3 cause brain dysfunction.

    Hyperthyroid patients have the highest levels of rT3. If rT3 really blocked the receptors, no one would ever be hyperthyroid. Think about it.

  • First the post was a suggestion if RT3 tests were of any use.

    I completely disagree with the following extract from your response above:-

    "The T3-only protocol is not for everyone, and some people have had serious side effects. Inability to think and remember anything (dementia), severe hair loss, muscle wasting, bone loss (osteoporosis), and high blood sugar (diabetes) are just a few of the side effects.

    Yet other patients claim this protocol gave them their lives back. How is that possible? Different biochemistries require different proportions of T3 and T4.

    Estradiol and SHBG rise to unnatural levels on the T3-only protocol.

    Who made this up? Are they benefiting financially? The cost of compounded T3 far exceeds the cost of generic T4 or desiccated thyroid. The reverse T3 ratio is a nonsensical number because it can be low for several different reasons, each requiring a different treatment."

    First, people who are thyroid hormone resistant (in that they have difficulty with levothyroxine or normal doses of T3) that they need super-physiologic doses of T3 to aid their recovery from clinical symptoms). Extract:

    Rather than being a hormone, T4 is a “pro-hormone.” That means that enzymes have to convert T4 to T3 before T4 benefits us. T4 is no more a hormone than beans in an unopened can are a food. For all practical purposes, canned beans become food only when a can opener frees them so you can eat them. Hence, T4, like canned beans, only potentially benefits us, but actually does so only after being freed from its metabolically unusable form.

    Your endocrinologist may say that T4 is a gentler way to get T3 into your body. This to me, however, is a specious argument. When taken properly, T3 can effect one as gently as T3 derived from T4."

    web.archive.org/web/2010103...

    It would seem to me that to force patients to only accept levothyroxine at any cost rather than see them recover on a T4/T3 combo, or T3 only or prescribe Natural Dessicated Thyroid Hormones containing all of the hormones a healthy gland would produce ie T4/T3/T2/T1 and calcitonin (helpful for bones) are failing in their duties as 'practitioners' when they don't listen to their patients and prescribe suitable products.

    We certainly wouldn't be on this forum if we were perfectly healthy and back to normal health with levothyroxine.

    Misrepresentation of the Active Thyroid Hormone, liothyronine, is doing a dis-service to people who take it to improve their lives, or to have a normal way of living without scare tactics which the above section seems to be and that is what it is - scaring and frightening people into submission and ill-health. while pocketing remuneration from Big Pharma.

    We patients don't want to know or care about the physiology of hormones - the only fact of concern is 'is it working?' 'am I symptom free' 'am I leading a normal healthy life and able to work and look after my family'.

    What about the poor souls who've taken their own lives ( I can name 3) or threatened to due to the poor care received and no-one bothering. There must be quite a few over the years. That is a very sad fact which most probably could be avoided with the right hormones and medical support.

    The brain contains the most T3 Receptor Cells and I believe the heart is next. Someone will correct me if my supposition is incorrect.

  • Umm, I think you're taking a lot of that post out of context. And there are some facts in your response that are debatable:

    1. There are T4 receptors and T4 induces physiologic responses as T4, so it is not just a prohormone, no matter how often that is repeated on the internet.

    2. There is very little T2 or T1 in NDT, nor is calcitonin of any use when taken orally.

    3. The entire site pushes T4 and T3 taken together, but in physiologic does, not T3-only. But even then, it says "Yet other patients claim this protocol gave them their lives back. How is that possible? Different biochemistries require different proportions of T3 and T4." That is hardly anti-T3 or anti-NDT.

    I have read enough posts over the years to be convinced that an extremely small minority do well on T3-only. My concern is the alarming number of posts I've also read of people who became much much worse following a T3-only protocol trying to clear their rT3, because they read it on the internet. They completely dismiss the benefits of T4 that many do get, because T4 has ALSO been misrepresented.

    I'm a patient and *I* care about the physiology because while not optimal on T4-only, NDT didn't make me feel that much better either. I've seen posts from others saying the exact same thing. I know my brain likes both T4 and T3. On T3-only, I have no memory. On T4-only, there are other problems like word recall.

  • Somehow, you are reading anti-T3 and pro-T4 in my post. That is NOT what I said. I personally take T4 + NDT. The link you posted to Lowe's site is all about how T4 doesn't work for a lot of people. I completely agree! What I'm trying to say is that T3-only and high doses of NDT don't work for a lot of people either. For people to get well, all dogma has to be put aside, and patients need to be allowed to try out different combinations to see what works for them. Claiming that T3 is the answer to all hypo problems is no different, to me, than claiming T4 is the answer. Too much T3 can cause horrendous damage to the body--ask any Graves' patient!

  • I agree with you that it is trial and error for each and everyone but the Associations guidelines don't think that at all and prescribe T4 only.

    I have never claimed that T3 is the answer to all. What I have said if members complain is to advise to try some T3 to whatever they are taking.

    I am not on here for an argument and everyone is entitled to their own opinion and members post helpful posts of what they found the best route for them.

    I have done the rounds of all of the different methods but have now found one that suits me best. I am lucky in that it works for me.

    I didn't claim that T3 is the answer to all hypo problems. In fact most people on T4 who aren't doing well DO find an improvement with the addition of some T3.

    I think there is some confusion here if you are talking about Graves Patients which I assume (as I know nothing about hyperthyroidism) that their body provides too much T3. That would of course be the cause of their clinical symptoms and their hyperthyroidism?. Just as hypo is a lack of T4.

    I am not suggesting overdosing on T3 because if any of us take fraction too much of any thyroid hormones our bodies react in an unpleasant way.

    With levo I was in and out of the A&E cardiac Dept like a yo-yo and it was the levo at a lowish dose which caused these severe palps. T3 calmed everything down and I haven't been to see my GP since re clinical symptoms. This is an expert's opinion:-

    And ". . . caused strokes"? If anything, the use of T3 may help prevent strokes. I scanned MEDLINE for studies on "T3" and "strokes" published between 1966 and 1997. These key words were mentioned in 43 publications. Most publications reported the beneficial effects of T3 on cardiovascular function. The word "stroke" was most often used in regard to the "stroke work in cardiac contractility" (a physiological description)—not in the sense of cerebrovascular accidents (strokes). I'll mention just a few representative publications. These suggest that it is urgent for the physician you mention—for his patients' welfare—to quickly update his knowledge.

    In one study, a researcher found that T3 levels were significantly lower in 42 of 65 stroke patients. [Liang, D.S.: Stroke and thyroid hormones. Chinese Journal of Neurology & Psychiatry, 24(6):352-354, 384, Dec., 1991] It is certainly possible that the low levels of T3 were partly responsible for the strokes. It is well-known that low thyroid hormone levels result in high blood fat levels, and high blood fat levels predispose patients to heart attacks and strokes. By lowering blood fat levels, the use of T3 is likely to help prevent, rather than cause, strokes in some of the above-mentioned physician's patients.

    The use of T3 is even beneficial in patients with the most frail heart conditions. Researchers in one study reported, "Triiodothyronine [T3] administration in patients undergoing cardiopulmonary bypass surgery is safe, may lessen the need for pharmacological (vasodilator) therapy, but may increase heart rate." [Vavouranakis, I., et al.: Triiodothyronine administration in coronary artery bypass surgery: effect on hemodynamics. Journal of Cardiovascular Surgery, 35(5):383-389, Oct., 1994]

    Many dotors pre 60's doctors did exactly the same, took patients clinical symptoms into consideration and prescribed NDT.

    I dont think it is useful to demand that one thyroid hormone is better than another. That's not true. It is only better for the person who gets well.

    I also don't think its beneficial to spread rumours or take non-scientific info as truth which frighten people into submission and they may not trial what might be a godsend to them.

    Publications. Dr. Lowe has authored more than 160 articles, scientific papers, and book chapters. His writings have appeared many journals, including Psychological Reports; Medical Science Monitor; the Journal of Behavior Therapy and Experimental Psychiatry; the American Journal of Pain Management; Anabolism—A Journal of Preventive Medicine; Medical Hypotheses; Lyon Méditerranée Médical: Médecine du Sud-Est; the British Medical Journal; the Journal of Myofascial Therapy; the Clinical Bulletin of Myofascial Therapy; the Massage Therapy Journal; the Journal of the American Chiropractic Association; and Thyroid Science. Trade papers such as Dynamic Chiropractic, the Chiropractic Journal, and others have published articles and monthly columns by Dr. Lowe.

    The authors of at least twenty-three books have cited or described Dr. Lowe's work. Among his own published books are Spasm, Your Guide to Metabolic Health, and The Metabolic Treatment of Fibromyalgia. Study Sphere gave Dr. Lowe its Excellence Award for his chapter in The Metabolic Treatment of Fibromyalgia in which he shows that fibromyalgia is not a psychiatric disorder. In the chapter, he refutes the notion that fibromyalgia is a mental or emotional disorder. He also argues that the misdiagnosis is usually a product of the psychological disturbance of physicians who make the misdiagnosis.

    Awards and Memberships. In 1977, the American Chiropractic Association awarded Dr. Lowe its Annual Scientific Paper Award. In 1992, for his contributions to the field of myofascial therapy, the National Association of Myofascial Trigger Point Therapists appointed him an honorary lifetime member. He has served as an official scientific reviewer on the International Reviewers' Panel of Medical Science Monitor, an international journal for experimental and clinical research. As a reviewer, he did critical reviews of submitted research papers in the fields of hypothyroidism and thyroid hormone resistance.

    Dr. Lowe is a member of the Board of Medical Advisors of Thyroid UK, and is a member of Index Copernicus Scientists, a global information networking system for scientists. He is Editor-in-Chief of the open-access journal Thyroid Science (www.ThyroidScience.com), which publishes papers on the full range of topics in thyroidology. He formerly served on the Advisory Board of Inside Texas Running Magazine and the Editorial Review Board of the Journal of Bodywork and Movement Therapies. He is a former editor of the Journal of Myofascial Therapy and the Clinical Bulletin of Myofascial Therapy.

    In December 2005, Dr. Lowe became a member of Index Copernicus Scientists upon invitation from its CEO Mark R. Graczynski, MD, PhD. Index Copernicus Scientists is a global information networking system for scientists, designed by and for scientists.

  • Just to clarify - I am not on T3 only. I am still taking 50mcg T4.

    Also pondering on jimh111 's comment re the body only producing 6mcg T3 daily. How then I am not flooded with T3 and hyperthyroid after taking 12.5 mcg T3 daily? Or even 18.75 as I am now. Clearly I am not (see above) as results show FT3 at only 4.13 (3.1 - 6.8). Not only that but my symptoms are still hypo, not hyper.

    The referenced articles seem to imply that T3 only dosing is unhelpful in most people, but that for some adding T3 can be useful. I am sticking to my regime for now, but very interested in this thread and hoping for more understanding about optimal treatment and also the impact of DIO2 and also the relevance or otherwise of rT3.

  • I think most people, if not improving on levo, find a benefit when T3 is added but the doctors are reluctant to prescribe and they are following the guidelines.

    Many on this forum have found great benefit from having T3 added and I only really recovered when I took T3 only. I take my dose once daily and am fortunate in that I have no clinical symptoms and feel well.

    Some may be thyroid hormone resistant and therefore will only get well on T3 only.

    Go to the date March 17, 2000 on the following link:

    web.archive.org/web/2010103...

  • Musicmonkey,

    Taking 12.5mcg T3 does not mean that 12.5mcg is absorbed.

  • Sorry for the delay in replying Clutter jimh111 Does this mean do you think, bearing in mind what jimh111 said above and below (i.e. that a low ratio of rT3 and having faulty DIO2 are of minimal significance) that I may have a Thyroid Hormone Resistance problem, or Resistance to Thyroid hormone' (RTH) ?

    If so, how easy/difficult would it be to confirm this? Would I need the help of an Endo?

  • Musicmonkey,

    I really don't know the answers to your questions.

  • Lol! Well in some ways that makes me feel better :) It's just that this keeps coming up as a possible reason for my symptoms and results when I post on here so am beginning to wonder......

    Thanks anyway!

    M x

  • I should clarify that my earlier post is strictly related to the usefulness of rT3 and DIO2 assays - I feel they are of little use, but sometimes they persuade an ill informed doctor to prescribe L-T3, perhaps doing the right thing for the wrong reason.

    This doesn't deny that there are many patients with severe symptoms who require large doses of T3 containing medicine. Dr Lowe correctly refers to peripheral thyroid hormone resistance, which affects organs other than the pituitary. The preferred term is 'resistance to thyroid hormone' (RTH) as thyroid hormone resistance might incorrectly suggest the hormone has the resistance. In Dr Lowe's case this might have been genetic as he was ill since childhood. In most cases the onset is later in life. I suspect many of these cases are caused by endocrine disrupting chemicals (EDCs).

    Whatever the cause of peripheral RTH treatment will require supra-physiological doses of thyroid hormone. If large doses of levothyroxine (L-T4) are used the deiodinases (working correctly) will reduce T4 to T3 conversion and increase the production of rT3. Thus L-T4 will not work in cases of RTH, T3 medication is needed. Patients often say they can't covert which is not true. They need higher levels of T3 but their body correctly tries to maintain normal levels. There is no conversion problem.

    A problem is that RTH affects different receptors to different extents and the alpha-1 receptors which are expressed to a greater extent in the heart are usually less resistant that the beta-1 receptors. This presents a problem in that if these patients take sufficient T3 to feel fine it may be too much for the heart. So we have a difficult situation, some patients will need high dose T3 medication simply to function but care has to be taken not to overstimulate the heart. It's a difficult problem as too little hormone will also lead to cardiac problems and no chance of a normal life.

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