how to calculate t3/reverse t3 ratio

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    I am a Gyn doctor starting to treat hypothyroidism. I have listened to your webinars on FAAFM and Bioidentical Hormone Initiative. My lab uses T3 reference range 71-180 ng/dL and reverse t3 reference range of 13.5-34.2 ng/dL. I have read in places that I want the ratio of T3/RT3 to be over 10. Is this correct or with these units should it be over 1? Thanks



    … uses the FT3/FT4 ratio to cull out some 20% with deiodenase problems.
    The units are in pmol/L not ng/dL.


    Dr. Evans

    You want to check Free T3 levels (rather than Total). Those are the ones used in the formula.
    Reverse T3 is a dysfunctional bodily response, designed to shut down the body under stress. It interferes with optimal thyroid function so the levels should be as low as possible.The easiest way is to explain to patients is to remove the decimal point and look for a 2:1 ratio of fT3:RT3.
    TSH 2.5
    free T4 1.0 (0.8-1.8)
    free T3 2.3 (2.3-4.5)
    Reverse T3 23

    In this case. fT3:RT3 are 1:1. These fT3 levels are low to begin with, and RT3 is blocking entry of it into the cells. At fT3 levels of 2.3, we wouldn’t want to see RT3 any higher than 11 or 12. Treatment here would involve raising T3 levels to the upper mid-range of normal, with RT3 decreasing. If you have any lab results to go over, feel free to present them.



    Hi, I have been going through major symptoms for years of which have recently been increased with extreme drops in my already low blood pressure. Here are my lab work ups completed on 9-8-12.

    Cortisol 8 a.m draw 11.4 range 6-19
    ACTH 8 a.m. draw 16.3 range 7.2-63.3
    T3 reverse 28
    Free T3 3.3
    Free 4 1.13
    TSH 3.060

    I have a thyroid nodule/goiter and ACTH stim test results may be o.k. (doctor did not understand the 1989 recommended interpretation).

    From what I understand, the ratio FT3:RT3 is 1.18:1 witch means hypothyroidism right?

    However, with the extreme chills, crashes (lethargic fatigue to immobilization) and drops in blood pressure I have an adrenal problem too, right? Is it the ATCH levels that are causing the crash due to their low normal range?
    I have had (please don’t laugh) 3 MRI’s all come out fine; so no evidence of pituitary tumor.

    BTW, I started taking licorice root this morning and feel much better, blood pressure is back up.

    Any help here would be greatly appreciated.


    Dr. Evans

    Yes, you clearly have adrenal insufficiency. A low morning fasting level of Cortisol, means you don’t have enough Cortisol to get you up in the morning, handle fasting from one meal to the next and combat stress throughout the day. Under stress, your body will then resort to Adrenaline, and you’ll get the shaky, hypoglycemic symptoms, blood pressure drops or postural hypotensive symptoms.
    Adrenal treatments can include botanicals (like glycyrrhiza), adrenal extracts (bovine usually) or pharmaceutical hydrocortisone (=bio-identical cortisol such as Cortef or a compounded sustained release Hydrocortisone). Increasing salt (a glass of lightly salted water in the morning) and/or Florinef to address Aldosterone deficiency might also be recommended.
    You also have levels indicating hypothyroidism (high/normal TSH as well as suboptimal fT3:RT3 levels).
    Make sure to get recommendations regarding your thyroid nodule. A specialist will tell you whether a FNA biopsy is warranted or not. Many nodules recede with appropriate thyroid medication. You should also have anti TG and anti TPO ABs checked to rule in/out Hashimoto’s thyroiditis.



    Can someone please help with test results?

    I’m taking 2 grains of naturethroid/day.
    My Ft3 is 5.0 (up from 2.6 – I forgot to skip my meds the day of the last test)
    My TSH is .001 (down from .92)
    My RT3 is 17

    Ferritin is 20 (up from 11 after 3x of supplements)
    D3 is 40 (up from 32)

    Doc is backing me down to 1 grain/day on Tuesdays and Saturdays.

    I’m a chronic dieter – did Atkins for 4 years and lost 100 lbs. Weight started creeping up in the last year or so.
    Thank you!



    Congratulations on using natural thyroid hormone replacements.
    The amount you are using may be OK, but check for hyper symptoms.
    I’m still looking for a published study of the medicated TSH response.
    It is commonly assumed it operates no different than the natural healthy response.
    I’m looking at these various diets and I find a problem with the description of food and nutrients, which is I think greatly oversimplified, designed not to offend a raft of commercial interests. If you can grow your own food that would be optimal, but finding local growers should be a priority. Processed food has a lot of issues, and the laws are not strong in protecting the people ingesting them. Almost anything in a factory box is questionable. What are they not telling you?
    Doctors want to draw blood and prescribe pills, not get you involved with healthy eating, avoiding toxins etc.



    Can someone please help me with calculating my ratio? I have tried numerous times and seem to keep getting a different number. This could of course be due to my brain fog.

    The values are as follows:
    T3 total 1.3 nmol/L (lab #1)
    T3 free 3.76 pmol/L (lab #1)
    T3 total 0.5 ng/mL (lab #2)
    Rt3 13.9 ng/d/L (lab #2)

    I am not sure aswell if I should use the free T3 (measured two weeks apart from the reverse T3) or the total T3 which was measured at the same time as the RT3.

    Thank you very much.



    From the sparse information you have presented not much can be said.

    rT3 should be compared to fT3, Read Dr. Evans note further up in this thread.



    The ratio I get is 2.7. I am not sure if I should be using these values as they were taken at two weeks apart at two different labs.
    In short, over the last year I have experienced a multitude of symptoms: hair loss, muscle aches, a rising CK level, diagnosed with a mitochondrial defect, and the most disturbing is facial myxedema. I was ruled out for GH excess via blood and an MRI. Each specialist has suspected hypothyroidism but of course by labs are within normal range. I am now on a medical leave as I have such brain fog. I am troubled by the changes in facial appearance. There has been no change in weight, but a substantial loss of muscle mass and strength. I am short of breath a lot, blood pressure is normal and temperature is 36.5C on average. To date I have seen several endocrinologists, cardiologist, respirologist, neurologist, rheumatologist, immunologist, oncologist, ENT, hematologist, and all have concluded that there is nothing wrong and that they can not explain the facial swelling or rising Ck levels. All imaging has been normal to rule out a more occult cause of the rising CK (mammogram, ct of chest, ultrasounds of thyroid, liver, abdomen, colonoscopy).

    I must also state that all of this started after an extremely stressful event last year. I noticed the facial changes 2 months after and they have continued to progress. I believe that I have thyroid resistance and would live very much to start on T3 or SRT3. I am unsure which one would be best for me and if I should be doing Wilsons Protocol or just regular T3. If anyone could provide some suggestions that would be greatly appreciated.



    “… Each specialist has suspected hypothyroidism but of course by labs are within normal range. ..”

    I suppose these guys never heard of sub-clinical- or sub-chemical hypothyroidism?

    Look at the two top topics one the left of this page.

    As medical practice typically is geared towards sales of available and hopefully profitable patented and synthetic wonder-cures, anything cheap-, natural- and simple is never even considered.

    Your symptoms clearly point to hypothyroidism, low body temp is a key indicator.
    There are variously quoted 30 to 50 symptoms of hypothyroidism. It may affect 25% of women over 50.

    Suppose you tried a natural thyroid hormone replacement, which is low cost and contains all normally occurring thyroid hormones, and has been in use for a 100+ years, and one of three things happened:
    1. Nothing,
    2. You became hyper for a few hours until the T3 burned off,
    3. You felt somewhat better.

    What conclusion could you then draw?
    1. You did not need it, or did not get enough of it?
    2. The dose was to big and maybe not needed?
    3. You need it, and maybe more?

    The body may need some time to adjust to it, and a gradual ramp-up is not a bad idea.

    Also consider the cause(es) of hypothyroidism, this could be auto-immune disorders, food intake which is toxic. I suppose you have been tested for Anti-Thyroid Peroxidase Antibodies (anti-TPO) and Antithyroglobulin Antibody (TgAb)?



    I have been hoping to find a moderately authoritative source for what the fT3/rT3 ratio should be and was at fist hopeful to find this but was disappointed to find more hand-waving, mostly useless information and am hoping someone around here might actually know something and can elaborate.

    I’ll start with the example provided by Dr. Evans on 10 August 2012. Dr. Evans, like most doctors discussion lab results, didn’t provide any units so we’re left guessing. The units I’ve added in comments are the most likely given the limited information.

    TSH = 2.5 (that appears to be referencing a typical range of about 0.5 to 4.5 milli-IU/L or micro-IU/mL)
    free T4 = 1.0 (that appears to be referencing a typical range of about 0.8 to 1.8 ng/dL)
    free T3 = 2.3 (that appears to be referencing a typical range of about 2.0 to 4.5 pg/mL)
    reverse T3 = 23 (that appears to be referencing a typical range of about 9 to 24 ng/dL)

    We are then directed to “remove the demical point and look for a 2:1 fT3/rT3 ratio.”

    Fine. Here we go.

    fT3 = 23 (this is now pg/centi-L)
    rt3 = 23 (ng/dL)

    fT3/rT3 is now 1:1, as stated, but the unit are (pg dL)/(ng centi-L) which is a factor of 0.01. The “real” ratio is 1:100, not 1:1.

    Why does this matter – because Dr. Evans never told us the units he thinks the 2:1 ratio should be in, never told us the units that his example numbers are in, and anyone coming here for information may be horribly mislead based on what they find.

    And, unfortunately for suzannai, we see a perfect example of why already. See suzannai’s posts on 9 May and 10 May below. Aside from the fact that her labs were taken 2 weeks apart, which is its own problem, she has quite straightforwardly taken Dr. Evans’ advice to “remove the demical point” and does the following calculation:

    free T3 = 3.76 pmol/L
    rT3 = 13.9 ng/dL

    Remove the decimal points and she gets: 376/139 = 2.7:1

    It’s right, isn’t it? That’s what the provided information suggested she do.

    No. It’s dead wrong.

    She needs to first convert the molar concentration of free T3 to a mass concentration using the molecular weight of free T3 which is 650.9776 g/mol.

    3.76 pmol/L x 650.9776 g/mol = 2.45 ng/L or 2.45 pg/mL.

    Now, dividing that new more useful expression of free T3 concentration by the rT3 concentration:

    (2.45 pg/mL) / (13.9 ng/dL) = 0.0176

    In Dr. Evan’s “units” this would appear to be 1.76:1, which is less than his stated goal of 2:1. So there may be a problem here.

    suzannai, I hope you follow up on this.

    If one visits other sights describing fT3/rT3 ratios units are similarly ignored or hand waived away, but most of them describe an ideal fT3/rT3 ratio of 20:1, not the 2:1 mentioned here. And, in real units (as in, the units cancel out) the goal ratio would appear to be 0.02. In this on example the molecular masses of fT3 and rT3 are the same, so we could also have converted them both to molar concentrations and arrived at the same answer. But if we were taking the ratio of two molecules with different molecular weights then we’d be further worried about whether or not our “magic” number provided with no other information is a mass ratio of a molecular ratio.

    Can we get a trained endocrinologist to explain, with units, in just one set of units, carried all the way through the calculation, what the ratio should be if those units are used? Unfortunately, suzannai has showed us where someone can easily be mislead into believe they are perfectly fine when they have a problem they need to follow up on or vice versa.



    Thanks for the molecular mass conversion.

    You will find a whole lot of authoritative information on the “rT3/T3” ratio on Pubmed.

    This ratio may be interesting in explaining why some single synthetic hormone substitution do not work as “nature” intended, and to put some number on something where the solution could be more obvious. Why waste time with reinventing the wheel?
    Regardless of these levels, which may well serve a scientific research purpose, using the wrong medication(s) will not solve the underlying issue.



    Thanks for the links. They were helpful, but as always just short of adequate.

    I don’t understand your comment: “Why waste time with reinventing the wheel?” The reason we’re “wasting time” is to GET IT RIGHT. The example posted above by Dr. Evans assumes a set of units (which he doesn’t state) and which are completely incompatible with the units that suzannai arrived with and she followed his direction and got the wrong result.

    You know what else doesn’t agree with Dr. Evans’ example posted above? The papers you referenced in your search. They, like a lot of other sites I mentioned, *appear* to be using units that indicate the healthy fT3/rT3 ratio is 20:1, not the 2:1 suggested by the Dr. above. Why do I say *appear*? Because they indicate in the paper that example FT3/rT3 ratios like 8.7 are too low – but they *never* say what a healthy level is. On Dr. Evans’ scale 8.7 would be a ratio so high one should seek immediate medical attention. So it matters.

    Following the example given above suzannai unknowingly followed directions *correctly* and got the wrong answer – which could have medical implications related to the decisions she makes based on that wrong answer. I hope she comes back and sees the further discussion here.

    And, since this thread started with a *doctor* asking how to calculate the ratio I think it’s more relevant to talk about calculating it right in this thread than it is to talk about treatments – especially if one is trying to consider a course of treatment based on the calculation.

    Now, for those interested in seeing how the wheel was invented, the paper referenced above uses units of pg/mL for FT3 and ng/mL for rT3. If one *corrects* the scale so that those two concentrations are in the *same* units then an example measurement in the paper becomes:

    FT3 = 1.85 pg/mL
    rT3 = 0.212 ng/mL, which I convert to 212 pg/mL (now the same units as FT3)

    Now, when FT3 and rT3 concentrations are in the *same units* the ratio is:

    FT3/rT3 = 1.85/212 = 0.0087

    But in the units they report:

    FT3/rT3 = 1.85/0.212 = 8.7

    So, the moral of the story is – depending on which doctor is speaking the ratio you are looking for *can* vary. That’s REALLY important to know. If you want to calculate the ratio *yourself* because you want to understand what’s going on (like me, who has a doctor who hand waived my results and left me responsible for my own diagnosis – which led to me ordering three tests he refused to order – paying for them out of pocket at a private lab – and finding massively elevated thyroid antibodies) then your best bet is to convert the units of either FT3 or rT3 so that they are both in the same units. Then the ratio you want to see is 0.02. If you’re below that, then you have an rT3 problem and should probably seek further testing to find out what’s causing it. You doctor will *most likely* think on a scale that multiplies that result by 1000, so you want to be at or above 20 when you multiply by 1000. The paper referenced uses this scale. Dr. Evans above does NOT use this scale, but a scale based on multiplying that result by 100.

    This is all because units matter.

    Sadly, while I’m 99% positive that everything I said is right, I can’t be 100% positive because NO ONE gives a “clinical” ratio for healthy FT3/rT3 *and* the units they used at the SAME TIME – at least in my search so far. If that paper refrerenced above had only said 20:1 is the healthy goal I’d be 100% positive. If Dr. Evans above had given real units for his 2:1 healthy goal, we’d again be 100% positive. Until then we’re left guessing and hoping we’re right.

    I can only hope that a trained endocrinologist will weigh in with a definitive reference AND that suzannai will come back and find out her FT3/rT3 ratio is too low.



    Finding a healthy reference for this ratio, as well as other thyroid numbers, as this is a catch-22 situation. This has been going on for quite a while.
    A population based study is needed, from a country(ies) with universal healthcare and with no commercial bias, and a practitioners ability to diagnose hypothyroidism without the aid of blood tests, thus only from a clinical presentation. I’d say this is a long shot, but perhaps the guys in and the people who did the Tayside, Scotland, studies may have saved data that can be used.

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