Non-detectable FT4?

Very odd set of thyroid results. Here are the last three:

Here is a comparison of the last three tests:

Date Dose TSH FT4 FT3

Feb 2017 55T3 0.01 4.5 7.5

2 Aug 2017 60T3 none none 10.9

7 Aug 2017 60T3 0.01 0.8 4.8

Important: Tests 1 & 3 were done in the morning, before any thyroid medication that day. Test 2 was done at midday, one hour after 20mcg of T3, plus 30mcg T3 at 3.30am that day.

So I believe that the second set of results can be discounted as unrepresentative.

But the latest result is still very odd. Both the FT4 and the FT3 look far too low to me. If anything, it would seem to suggest that I'm under-medicated, not over-medicated.

Can anyone suggest an explanation for such odd results?

11 Replies

When on T3 alone its not odd to have a non existant TSH and a low t4

Your t3 level still seems low what symptoms do you have

Yes, I'm not worried about the TSH and I expect low T4 but not THIS low. And it makes no sense at all for the FT3 to be lower, much lower, on 60mcg T3 than on 55mcg.

Symptoms include faint, dizzy, slight SOB. (Plus of course all the usual hypo symptoms of fatigue, insomnia, etc.) There was also some nausea but I suspect that was down to a supplement with a very high level of D3 that I was not able to tolerate.

I'm puzzled to say the least.


Your thyroid function has obviously declined between Feb and Aug and that is why FT3 is lower despite the 5mcg dose increase which is really very small.

FT4 is low because you are taking T3 direct.

Clutter, this the response of my respiratory consultant at the Brompton:

"To my (inexpert eyes), you’re getting T4 suppression secondary to long term TSH suppression. Prob because T3 has been running high for some time?"

What's your view on that? Thanks.


He is indeed inexpert about thyroid. TSH is suppressed because pituitary detects sufficient thyroid hormone. FT4 is suppressed because you are taking T3 direct. There is no need for T4 which is a storage hormone when you are taking T3 direct.

Good, that agrees with my understanding.

Another question then: what might cause thyroid function to decline? Probably a 'how long is a piece of string' question, but I ask it nevertheless!


It's just a progression of the failure you are already experiencing which necessitates you take T3. Hashimoto's is the most common reason but thyroid also declines with age.

It also occurs to me that for much of this year I have been experiencing extreme physical and emotional stress - we're moving house! Long-distance. Combining two houses into one. Need I say more? Plus I flung myself off a chair and severely wrenched my leg. Plus this was 2 weeks before a wonderful, exciting but stressful and exhausting 5 day trip on the Orient Express to Venice, with just 2 days in Venice. Oh, and I'm getting physio treatment for a shoulder impingement. And the house-move related stress will continue for many months to come yet.

So... I guess this ain't doing my thyroid, or my adrenals, much good! But what to do? I doubt just lobbing more T3 at the problem would be the best idea. Or is it? I do need steroids from time to time (several other conditions besides hypo) - is it time to support the adrenals with some low-dose steroids (albeit very reluctantly, but sometimes needs must).

I may have to endure a visit to the endo, perhaps for cortisol and aldosterone tests but would much rather avoid him if possible!

Your advice/thoughts would be much appreciated.


I doubt stress is why your FT3 has dropped but stress can affect adrenals. I don't know enough about adrenals to advise. If you don't feel well with FT3 4.8 there is scope to increase dose. I think it's unlikely increasing by 10mcg will send FT3 over range.

maybe the t3 pills you have been given are not up to standard

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