Question about reverse T3: I am in a pickle... - Thyroid UK

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Question about reverse T3

LavaFlowing profile image
11 Replies

I am in a pickle awaiting a blood test and have a question regarding reverse T3. I’d tried to go off my thyroid meds following years of doing pretty well on 25 mcg Levothyroxine and 10 mcg Liothyronine. My TSH, T3, rT3 and T4 have always been in range even when symptoms were awful. The small doses of Levo and Lio made a big difference (although I wonder if my doctor didn’t give enough Levo before deciding I didn’t convert well and adding Lio). Anyway, the attempt to go off meds went terribly and I’ve been adding back since early July. I decided to increase my Lio and reached 20 mcg in mid Aug, still with 25 mcg Levo. I added another 5 mcg in mid Sept because I was still having some symptoms, but I quickly pulled back to 20 mcg when I finally found a doctor in my new location and she ordered a blood test. I didn’t want the newly added 5 mcg to confuse things. Turns out there was a misfire and the lab didn’t receive her request so I’ll go next week instead…. Meanwhile, I’m having symptoms again. I wonder if my body is missing that additional 5 mcg it had for a couple weeks, or maybe I have high rT3? Can that be caused by taking too much Lio? Glad I’ll have tests next week and interested in your thoughts to help determine how much to take until then. Thank you!

11 Replies
diogenes profile image

rT3 is produced from T4 not T3. Its only value is to indicate if you are overdosing on T4, or otherwise have a nonthyroidal illness that is directly raising it to higher levels. rT3 values should always be valueless if the two situations above are not happening. The nonthyroidal illness should be obvious to you anyway.

greygoose profile image

rT3 doesn't cause symptoms, anyway. It is inert and only stays in the body for a couple of hours before being converted to T2. :)

SlowDragon profile image

What’s the highest dose levothyroxine you were on before T3 was added

Standard starter dose of levothyroxine is 50mcg

Typically dose is increased slowly upwards in 25mcg steps until symptoms improve

Guidelines on eventual dose levothyroxine required is approx 1.6mcg levothyroxine per kilo per day

How much do you weigh in kilo approx

Essential to regularly retest vitamin D, folate, ferritin and B12

When were these last tested

What vitamin supplements are you currently taking

For full Thyroid evaluation you need TSH, FT4 and FT3 plus both TPO and TG thyroid antibodies tested.

Very important to test vitamin D, folate, ferritin and B12

Low vitamin levels are extremely common, especially with autoimmune thyroid disease (Hashimoto’s or Ord’s thyroiditis)

Low vitamin levels common as we get older too

Recommended on here that all thyroid blood tests should ideally be done as early as possible in morning and before eating or drinking anything other than water and last dose levothyroxine 24 hours before test

Split T3 day before test into 2 or 3 smaller doses spread through day and take last 1/3rd approx 8-12 hours before test

This gives highest TSH, lowest FT4 and most consistent results. (Patient to patient tip)

Private tests are available as NHS currently rarely tests Ft3 or all relevant vitamins

List of private testing options

Medichecks Thyroid plus antibodies and vitamins

Blue Horizon Thyroid Premium Gold includes antibodies, cortisol and vitamins by DIY fingerprick test

LavaFlowing profile image
LavaFlowing in reply to SlowDragon

Thanks for all of this. Highest levo was 25 mcg. Iron and vitamins all within range for years because I supplement. Will have tested again next week.

SlowDragon profile image
SlowDragonAdministrator in reply to LavaFlowing

Are you in U.K.?

Approx age?

Approx weight

25mcg is ludicrously small dose levothyroxine

Levothyroxine doesn’t “top up” failing thyroid, it replaces it.

guidelines on dose levothyroxine by weight

Even if we frequently don’t start on full replacement dose, most people need to increase levothyroxine dose slowly upwards in 25mcg steps (retesting 6-8 weeks after each increase) until eventually on, or near full replacement dose

NICE guidelines on full replacement dose


Consider starting levothyroxine at a dosage of 1.6 micrograms per kilogram of body weight per day (rounded to the nearest 25 micrograms) for adults under 65 with primary hypothyroidism and no history of cardiovascular disease.

Also here

Traditionally we have tended to start patients on a low dose of levothyroxine and titrate it up over a period of months. RCT evidence suggests that for the majority of patients this is not necessary and may waste resources.

For patients aged >60y or with ischaemic heart disease, start levothyroxine at 25–50μg daily and titrate up every 3 to 6 weeks as tolerated.

For ALL other patients start at full replacement dose. For most this will equate to 1.6 μg/kg/day (approximately 100μg for a 60kg woman and 125μg for a 75kg man).

If you are starting treatment for subclinical hypothyroidism, this article advises starting at a dose close to the full treatment dose on the basis that it is difficult to assess symptom response unless a therapeutic dose has been trialled.

BMJ also clear on dose required

LavaFlowing profile image

I’m in the US. Age 50, 140 pounds. Definitely should’ve tried more Levo before adding Lio. Not wanting to go back and try that now, given how quickly symptoms appear and how long it takes them to go away, unless there’s a great reason?

SlowDragon profile image
SlowDragonAdministrator in reply to LavaFlowing

So you can just increase levothyroxine by 25mcg

Wait minimum 6-8 weeks before retesting

Always test as early as possible in morning before eating or drinking anything other than water and last dose levothyroxine 24 hours before test

Taking almost any dose T3 significantly reduces TSH

Essential to test vitamin levels too

SlowDragon profile image
SlowDragonAdministrator in reply to LavaFlowing

140lbs = 63kilo

On JUST levothyroxine you were likely to need 100mcg levothyroxine

On levothyroxine plus T3…..perhaps 62.5mcg or 75mcg levothyroxine

We should only increase levothyroxine in maximum of 25mcg

Having been left very under medicated, you might need to increase even more slowly by 12.5mcg for 6-8 weeks first

LavaFlowing profile image
LavaFlowing in reply to SlowDragon

Thank you! That’s so helpful to know. Is it better/healthier to do that than just work with T3?

SlowDragon profile image
SlowDragonAdministrator in reply to LavaFlowing

Majority of patients do fine on just levothyroxine

Only about 10- 20% of patients need addition of T3 or NDT

Majority of these will be fine on mainly levothyroxine, plus small dose T3….80% -90% levothyroxine and 10%-20% T3 …..aiming for Ft4 and Ft3 at least 50-60% through range

Some patients on levothyroxine plus T3, need higher dose T3 and smaller dose levothyroxine.


A much smaller number of patients can’t tolerate levothyroxine at all and need just T3

It’s all trial and error

But initially everyone starts on just levothyroxine and increases dose upwards (assuming they have a doctor who knows how to treat hypothyroidism)

Any thyroid hormones need OPTIMAL vitamin levels to work well

Essential to test vitamin levels at least annually

If cause of hypothyroidism is autoimmune thyroid disease also called Hashimoto’s diagnosed by high thyroid antibodies, then at least 80% find strictly gluten free diet helps, often significantly, or is absolutely essential

But always get coeliac blood test done before considering trial on strictly gluten free diet

LavaFlowing profile image
LavaFlowing in reply to SlowDragon

Thank you again.

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