Thyroid UK
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rT3 dominance?

I have been wondering lately if I could be suffering from rT3 dominance.

I have read that a lot of things can cause rT3 pooling: low cortisol (I have been diagnosed with adrenal fatigue), blood sugar issues, vitamin and mineral deficiencies...

I know some labs offer rT3 testing, but they seem few and far between. However, it seems you can self-diagnose based on some telling signs like taking more and more thyroid meds, having seemingly normal FTs, yet remaining hypothyroid, while being told by most docs that has nothing to do with your thyroid condition as your labs look normal...

Has anyone here self-diagnosed and self-treated rT3? If so, how?

Most of the information available seems to be from the US, where doctors treating rT3 dominance seem to prefer using slow release T3 instead of fast acting drugs like Cytomel. However, as far as I know, slow release T3 is not available in Europe, at least not in continental Europe. It's not readily available in pill form but needs to be prepared by a compounding pharmacy, it's a prescription drug only, and I doubt any doctor near me would be willing to prescribe it, or even test my rT3 levels...

My doctor is a so called Hertoghe doctor, and they are supposed to be better than most mainstream doctors. It's true that they prescribe NDT and various other hormones, but they don't seem to know anything about rt3, and never test for it. They also seem to think that NDT is ideal for everyone, and that nobody should ever need to take synthetic T4 or T3 drugs once they are on NDT.

When I went to see this doctor for the second time, to discuss my test results (blood and 24 h urine) and treatment plan, the doctor told me both my FTs were low in blood, as well as in 24 h urine, which meant that I was not converting T4 to T3.

However, today, I cannot help but wonder if that was really the case...? What I mean is: if I was not converting T4 to T3 properly, would I not have high, or even excessive, levels of FT4, along with low levels of FT3, on a dose of 200 mcg of thyroxine daily...?

I am beginning to ask myself if low levels of both FT4 and FT3 meant that most of the T4 was converted to rT3, not FT3? rT3 will compete with FT3 for the same cell receptors, blocking the action of FT3. That would explain my low levels of both FTs, along with some remaining hypo symptoms.

I felt good on NDT for the first six months, after years on T4 drugs, but then things started going downhill...I have had to raise it several times, and today I need 8 grains daily just to feel functional. I don't have a single hyper symptom. On 5 grains of NDT daily, my FTs were at the bottom of range. It seems I need to raise my dose from time to time to get the same effect; strangely enough, though, another grain does not seem to make that much of a difference....which also makes me wonder if every raise only makes my body produce more rT3, so a vicious circle...?

6 Replies


Low TSH, high FT4 and low FT3 indicates poor conversion. Low FT4 and low FT3 indicates undermedication. If FT4 is low there isn't sufficient to convert.

You can order rT3 tests from Blue Horizon and Genova via

rT3 is usually treated by stopping T4 and taking T3 only for 3-4 months. The smaller the dose of T3 you can manage on the quicker rT3 should clear. It doesn't have to be slow release T3.

I suspected I had a build up of T4 but don't know that it was rT3 as I didn't test. I didn't feel any better 8 weeks off T4 on T3 only and stopped T3 too. By the endo of the 2nd week off T3 symptoms started clearing and had completely resolved by the end of the 3rd week. When I resumed T4 I had adverse symptoms within hours and 2 days after adding T3 adversed symptoms were calmed.


Interesting, thanks Clutter! I never imagined you could be under medicated on 8 grains of NDT...but my doctor has patients on as much as 10-11 grains of NDT daily. Some seem to require more than others, although many seem to think that you "should" never have to take more than 3-5 grains daily...



People need as much as they need. 3-5 grains appears to be the average dose taken and it's ridiculous for someone to say that one should never take more than xyz dose.



You have provided a lot of info to think about but need test results.

Post latest thyroid hormone//iron //nutrient blood test results complete with ranges (numbers in brackets) for members to comment.


Ok, these are my latest lab results, from 9 February 2016 (on 8 grains of Erfa and 4 mg of Medrol daily for adrenal fatigue), plus Biovea multivitamin for women (it's only now that I realise some of these results are really worrying, to say the least). I had blood drawn at 8 am as instructed.

aldosterone 42 ng/L (40-300)

iodine 357 ug/24h (170-280) so seriously out of range (NDT???)

25-hydroxy-vitamin D 35.0 ug/L (30-60; optimal according to doc: 50)

vit A 41.1 ug/dL (43-111; optimal levels 90-100 according to doctor)

vit E 9.0 ug/mL (10.0-19.0; should be at least 12.5 according to doc)

vit B12 416 ng/L (300-835; ideal levels according to doctor 550-800)

selenium 127 ug/L (90-143)

zinc 99 ug/dL (84-135)

copper 127 ug/dL (86-148)

magnesium 4.99 mg/dL (4.40-5.80)

TSH <0.01 mU/L (0.3-4.5)

free T3 5.88 pmol/L (3.23-6.47)

free T4 15.01 pmol/L (9.03-23.22)

free cortisol (8 am) 14.1 ug/L (10-30) suppressive effect of Medrol???

Based on these labs, my doctor prescribed vit B12 injections and vit A.

Just to complete the picture, the results of the 24 h urine analysis:

T3 1120 pmol/24 h (800-2500; ideal levels 1600-1900 according to doc); compared to 2011 before I was put on NDT, on 200 mcg of T4 daily: 824 (800-2500)

T4 1380 pmol/24h (550-3160; ideal levels 2400-2500 according to doc); compared to before going on NDT, on 200 mcg of T4 daily: 1100 pmol/24 h (550-3160)

cortisol 30.5 ug/24h (10-100)



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Wow... great tests and I agree with the levels suggested by your doctor.

I supplement D3 with K2, Vit B12 in the form of methylcobalamin but you are now having injections. Why is Iodine so elevated ? Is it in your multivit ? ?Elevated iodine can reduce the enzyme called "thyroid peroxidase" required to produce thyroid hormones and should be balanced with selenium.

Your TSH, T4 & T3 are all good. TSH & T4 are generally lower when medicating T3 & your T3 (active hormone) is a good level in range..We can have good results and still experience hypothyroid symptoms for a number of reasons.

Low levels of both T4 & T3 would mean not enough hormone replacement. High T4 & low T3 would mean not good conversation and possible elevated RT3.

There is no mention of iron levels. Have you had ferritin levels tested ? ? Optimal levels are important as iron is in the enzyme "thyroid peroxidase" mentioned above.

Some need a combination of meds as just taking either NDT or synthetic may not work for them.

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