Thyroid Disorders Community
26.1k Members
Avatar universal

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

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
3 Responses
649848 tn?1534633700
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.
Avatar universal
T4 free range per lab 0.8 - 1.8. Thank you for your response Barb.
649848 tn?1534633700
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 it's very unfortunate that your doctor is ordering a test as outdated as TSH w/reflex FT4 and not the useful FT4 and FT3 tests.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?
Have an Answer?
Top Thyroid Answerers
649848 tn?1534633700
Avatar universal
1756321 tn?1547095325
Queensland, Australia
Learn About Top Answerers
Didn't find the answer you were looking for?
Ask a question
Popular Resources
We tapped the CDC for information on what you need to know about radiation exposure
Endocrinologist Mark Lupo, MD, answers 10 questions about thyroid disorders and how to treat them
For people with Obsessive-Compulsive Disorder (OCD), the COVID-19 pandemic can be particularly challenging.
A list of national and international resources and hotlines to help connect you to needed health and medical services.
Here’s how your baby’s growing in your body each week.
These common ADD/ADHD myths could already be hurting your child