Low TSH, T4 free good, what does this mean?

[kmcc21]

I was diagnosed with Graves 17 years ago. I was given radioactive iodine to control and have been on Synthroid ever since. 6 months my Dr. reviewed blood tests and reduced my prescription. I do not see the results. I had a follow up test a week ago. My Dr. has reduced my med levels again. TSH w/reflex FT4 is .02mlU/L, T4 Free is 1.5 ng/dL. If my T4 is good as test indicates why would the TSH be so low ? and why would the Doctor reduce my meds?
Thank you

[Barb135]

Your doctor was probably reacting to the TSH, but your FT4 was very high at 70% of the range.  

Most of us find that we feel best with FT4 at about 50% of the range and FT3 in the upper half to upper third of its range... it's very unfortunate that your doctor is ordering a test as outdated as TSH w/reflex FT4 and not the useful FT4 and FT3 tests.

Are you having any symptoms of either, over or under medication?

[kmcc21]

T4 free range per lab 0.8 - 1.8. Thank you for your response Barb.

[Barb135]

What is the reference range for the Free T4?  Reference ranges vary lab to lab and have to come from your own reports.

TSH often becomes suppressed once we're on an optimal dosage of thyroid medication. TSH also can fluctuate by as much as 75% over the course, of a day, so if your doctor is dosing your medication, based solely on your TSH, as it appears he's doing, he's trying to shoot a moving target.  

Have you ever had a Free T3 test?  Free T3 is the actual thyroid hormone that the individual cells in our body uses and it correlates best with symptoms.  Free T4 is a storage hormone and must be converted to Free T3 in order to be used.

Just to put your mind at ease, my own TSH has been < 0.01 - 0.01 for the past 7 years and as long as my Free T4 and Free T3 are good, we don't worry about it.