Adding to my back again post

[Dryski]

The six weeks i went without levo this was the full results. Free t3 stayed good at 2.70 range of 2.18 to 3.98, my free t4 dropped drastically to .78 range .76 to 1.46 and my tsh shot up to 9.12 range .36 tp 3.74. My question is what causes the free t4 to drop so drastically without meds but the free t3 to maintain? My doctor said it's normal for healthy people to fluctuate like that but till endo appointment I am back on 37.5 levo. Any opinions welcome. I was previously on meds for 15 years because something isn't right. I think had I gone eight weeks I would have bottomed out. I've never had antibodies checked in the past. Does this look like primary, secondary or any opinions from your professional knowledge?

[tattybogle]

My question is what causes the free t4 to drop so drastically without meds but the free t3 to maintain?

partly because :

TSH increases the thyroids output of 'ready made' T3

(this is also why in early stages of thyroid failure as fT4 level falls and TSH rises , the fT3 level is maintained .... for a while till thyroid can't manage to keep that up either )

and also ,the deiodinase's (that convert T4 to T3 , and T3 to T2 ) have some effect ... (they are affected by fT4 levels and TSH levels)

[Dryski in reply to tattybogle]

Thanks for the explanation. So without meds my free t4 bottoms out and I would skate by on just free t3 but not for very long when reserves dry up. Makes sense.