Everyone makes Reverse T3 (RT3)–an inactive thyroid hormone. It’s a way to clear out excess T4 when your body isn’t needing that extra storage hormone. i.e. instead of the T4 converting to the active T3, your body (and specifically your liver), will convert it to RT3. If someone without a thyroid problem gets the flu, up goes the RT3 to conserve energy. If someone has a bodily injury, up goes the RT3 to conserve energy.
And thyroid patients seem to see their RT3 go up in the presence of low iron or a cortisol issue.
But if you think about it, why doesn’t it go down faster when we decrease our T4? T4 has a half life of one week, yet it can take 8 – 14 weeks for RT3 to go down....
Cont on :http://www.stopthethyroidmadness.com/2014/02/08/rt3-hidden-pool/