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How to dose when low FT3 and extremely low TSH?


For the past 2 months I was on 88 mcg Synthroid and 20 mcg Levothyroxine. I have non-autoimmune hypothyroidism (negative for antibodies at all tests over the past 2-3 years). Taken at 1:00 pm. My latest labs showed:

TSH: 0.006 (0.4-4.5)
FT3: 2.6 (range 2.3-4.2)
FT4: 1.7 (0.8-1.8)
RT3: 35.2 (10-24)

I skipped my Liothyronine dosage the day of the test, so it had been about 26-27 hours since my last dose of T3. My doctor wants to lower my Levothyroxine dosage to 25 mcg and keep Liothyronine at the same dosage due to my TSH being so low, but she knows the Liothyronine is making a big difference for me.

Would this be a good move to fix my RT3/FT3? I've been doing better but don't feel "normal" or how I did before my thyroid went out of whack. All other lab numbers were within range except my Ferritin being low-normal at 37. I asked her about how to increase my FT3 and she said first we need to get a handle on my TSH, and that lowering the dosage of Levothyroxine should also help my RT3 come down.

Thanks for your time!
2 Responses
Avatar universal
In the untreated state, there is a continuous low flow of thyroid hormone that creates an equilibrium among the hypothalamus/pituitary/thyroid gland.  When taking a daily replacement amount of thyroid med all at once, that has a suppressive effect on the TSH output, since there is no need for TSH stimulation of the thyroid gland.  Although frequently interpreted as hyperthyroidism, such a suppressed TSH does not mean hyperthyroidism unless there are hyper symptoms due to excessive levels of Free T4 and Free T3.  There are a number of members, including myself, that have had suppressed TSH for many years without ever having hyper symptoms.   Accordingly TSH should not be relied on to determine the medication dosage.  Dosage should be adjusted as needed to relieve hypo symptoms, not based on lab test results.  

Since all of your Free T4 and Free T3 is the result of the thyroid medication, I would not suggest reducing the T4 dosage to 25.  Mid-range is a good target for Free T4, so reducing the level from 1.7 to 1.3 would require approx. a 25% reduction in T4 med, so it seems that a dosage of 50-62.5 would be more appropriate.  Along with that, keeping the same T3 dosage would likely reduce your Free T3, due to less available for conversion, when you rally want to increase your T3 dosage, and raise your Free T3 level, and increase your Free T3 to RT3 ratio.  After these changes if your RT3 remains high, then a further decrease in T4 med might be required.  

So I think that you are going to have to convince your doctor that the suppressed TSH is not a concern, in order to get where you need to be.  I think you could make good use of the link I think I gave you previously.


In the paper, in Rec. 10 on page 13, there is more than adequate scientific evidence that TSH suppression is not a cause for concern.   Also, note Ref. 36, which concluded from a study that “Measurements of serum concentrations of total thyroxine, analogue free thyroxine, total  triiodothyronine, analogue free triiodothyronine, and thyroidstimulating hormone, made with a sensitive immunoradiometric assay, did not, except in patients with gross abnormalities, distinguish euthyroid patients from those who were receiving inadequate or excessive replacement. These measurements are therefore of little, if any, value in monitoring patients receiving thyroxine replacement.”

Your ferritin level was also much too low so you need to supplement with a good form of iron to optimize to at least 100.  I have found Vitron C to be a good iron supplement since it contains 65 mg of iron and also Vitamin C to help prevent possible stomach distress from the iron.    Other good forms are ferrous fumarate, ferrous bisglycinate, and ferrous sulfate.  

Were you tested for Vitamin D and B12?

I have showed my doctor that reference before but she still is uncomfortable with my TSH staying consistently that low. She said she is fine with my TSH being slightly lower than normal, but is concerned it's almost "undetectable". I am unsure as to whether I should try to find a new physician. She told me she wants me to try the 25 mcg for 8 weeks and see how i'm feeling, if I really wasn't doing well I believe she would raise it again.

I will try taking the iron! Hopefully that helps. My Vit D and B12 were both in good ranges. I take supplements for both.
Avatar universal
If you drop your T4 med to 25 mcg and do not increase your T3 med significantly you are going to regress.  

I think I would mention to the doctor that a suppressed TSH is of concern only in an untreated thyroid patient, because in that situation it is a signal of excessive levels of FT4 and FT3.   With a thyroid patient taking full daily replacement doses of thyroid med, what does a suppressed (or almost nonexistent) TSH supposedly indicate?  TSH cannot be shown to correlate well with either FT4 or FT3, and certainly your FT4 and FT3 are not excessive, even with the suppressed TSH.  So, what function would be adversely affected by a lack of TSH?  The doctor won't have an answer for that, only her misgivings, based on not understanding what daily replacement doses of thyroid med do to the TSH level.

Following is another source of info on suppressed TSH.

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