Thyroid UK

Is Reverse T3 a problem indicating a Conversion Issue?

I've been gradually increasing dose of T4 from 75 - 100 mcg after being diagnosed with Hashimoto's a few months ago. After my last lab work, for the first time, I measured my Reverse T3, and it was 19 (ref range of 8-25). Does a Reverse T3 in the upper-mid portion of the range suggest that I am having conversion issues? In other words, for Reverse T3, is conversion typically good as long as we fall within the stanard lab ranges, or should I be shooting to have this number at the lower end of the reference range?

5 Replies

Milnerb1, T4 converts to T3 and rT3, it's the body's brake on converting too much T3. rT3 over range can be a problem but yours is comfortably within range and isn't high.

Low TSH + high in range FT4 + low FT3 indicates poor conversion. If you post your thyroid results with ranges I'll have a look.


Here's my full history. I am a 45 year old male that was recently diagonsed with Hashimotos based on the following labs and typical hypo symtoms:

TSH - 2.4 (.35 - 4.94)

FT3 - 3.2 (2.3 - 4.2)

T3 - 98 (58 - 159)

FT4 - .75 (.7 - 1.8)

T4 - 4.1 (4.5 - 12.5)

TP Autoantibodies - 42 (5 - 25)

Thyroglobulin Ab - 376

My doctor put me on 75 mg of Levothrtroxine a month ago. After waiting a full month, my follow-up labs were as follows:

TSH - 1.4 (.35 - 4.94) - Decreased to seemingly good range

T3 - 95 (58 - 159) - DECREASED from 98

T4 - 4.8 (4.5 - 12.5) - Increased slightly but still at low end of range

TP Autoantibodies - 60 (5 - 25) - Increased

Thyroglobulin Ab - 422 - Increased significantly

After another month on 100 mcg Levo, my follow up labs were:

TSH - .9 (.35 - 4.94) - significant improvement

FT3 - 3.2 (2.3 - 4.2) - no improvement

T3 - 96 (58 - 159) - no improvement

FT4 - .95 (.7 - 1.8) - no improvement

T4 - 4.8 (4.5 - 12.5) - no improvement

TP Autoantibodies - 60 (5 - 25)

Thyroglobulin Ab - 429

Reverse T3 -19 (8-25)

Now, I'm taking 5 mcg of cytomel and have been experimenting with 10 mcg for a few days. Still don't feel much (if any) improvement of symptoms.

My main questions is whether I should increase T3 or increase T4 dose. T3 seems to be a more active, but since my T4 insn't that high yet, and since I don't seem to be having conversion issues, perhaps more T4 would be a better approach.

Thanks so much for your assistance thinking through this!


Milnerb, It takes up to six weeks to feel the impact of a dose and although TSH responds quickly, FT4 and FT3 are slower. Taking oral T3 dampens FT4 as higher FT4 levels aren't required for conversion when T3 is obtained directly.

I'd increase T3 as your FT3 is low and increasing T4 may raise your rT3. 10mcg T3 is equivalent to 30mcg T4. Like T4 it takes time to metabolise and work on symptoms which can lag behind good biochemistry by a couple of months.


This is helpful. I was thinking that, since T3 is the active hormone, that it would act almost immediately and improve symptoms right away. Is that not the case?


Milnerb, no, you may *feel* a dose after ingestion as it temporarily raises pulse and heart rate but it takes 36/48 hours to get from the blood into the cells before it starts working on symptoms and, like Levothyroxine, needs several weeks to metabolise. Having said that, some people do report immediate improvement, particularly in energy and brain fog. It's best to assume that improvement will be gradual.

I felt improvement in brain fog and cognition within a week of adding T3 to T4 but my FT3 was below range so my brain probably soaked it up like a sponge. There was no improvement in physical symptoms for several months but that may have been due to other issues which needed dealing with.


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