Reasons for having Reverse T3 test please.

[Annealise]

Have recently come across reverse T3 on here and wondered in what circumstances you would have this test done. Can it tell if you are not converting T4 to T3?

[Clutter]

Annealise,

rT3 levels won't indicate what sort of conversion a person has. A poor converter will have low TSH, high FT4 and low FT3.

T4 converts to T3 and reverse T3 (rT3). rT3 is the body's brake on preventing too much T4 converting to T3.

rT3 isn't tested on NHS but a lot of American thyroid advocates are very keen on rT3 testing. The thinking appears to be that high levels of unconverted Levothyroxine can cause high rT3 which will block T3 receptors. Decreasing the amount of T4 taken or switching to T3 only for 3-4 months is supposed to clear high rT3.

[SeasideSusie Remembering]

Annealise If you want to know if you are converting T4 to T3 then you need FT4 and FT3 tests done at the same time. If your FT4 is a lot higher in range, with a lowish FT3 then that points to poor conversion. If you divide the results FT4 by FT3 and the ratio of FT4:FT3 is more than 4:1 that again points to poor conversion. A thyroid urine test measures what gets into the cells so if a reasonable amount of T4 is getting into the cells but the T3 is showing at the very bottom of the range, again it would indicate poor conversion.

I'm not an expert on rT3, but my own experience was that my TSH was always suppressed, my FT4 was always over range (as high as 29 with a range of 12-22) and my FT3 was nearer the lower end of it's range, completely out of balance with FT4. I took this to be poor conversion but wasn't able to do a rT3 test at the time.

By the time I was able to do a rT3 test I had already been adding T3 to my Levo for 12 months and my FT4 had reduced to in range and FT3 increased to the top quarter a of range. lt showed rT3 at the very top of it's range so I think I'd had rT3 all along and adding the Levo was gradually bringing it down.