Low tsh with normal T-4

[zapped77]

I was diagnosed with hyperthyroidism in 1974 which was treated with radioactive iodine.  I had lost 13 pounds over a short period of time plus other related symptoms.  About six weeks later I had tremendous water gain and looked as if I had Downs Syndrome.  Tests showed by thyroid had been either completely or close to completely zapped.  I was put on .200 mcg of Synthroid.  I continued on that for about a decade when my doctor said my TSH was low and lowered me to .175 mcg.  This went on for several years.  A few years ago I was lowered to .150mcgs.  My TSH continued to be in the .03 range.  In the last six months my TSH went to zero.  However, my T-4 remained in the 4.75 range.  What makes my TSH so low?  (Last spring my doctor mistakenly refilled my Synthroid prescription at .50 instead of .150.  A few weeks later my TSH was over 8 and my T-4 at .03.)  I started taking my regular dose but the TSH results after that were at 0.  She has put me on .125mcg.  


This discussion is related to Confusing TSH results w/ Hashimotos.