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Thyroid UK
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Low Free T3


I've been looking for a posting with results similar to mine. Does anyone have an idea why my Free T3 (in the attached image) is on the low side but Free T4 appears normal?

Also, the following are my results from 3 months prior, Free T3 is higher:

TSH H 5.00 (0.27 - 4.20 mIU/L)

T4 Total 75.9 (64.5 - 142.0 nmol/L)

Free T4 16.53 (12 - 22 pmol/L)

Free T3 5.30 (3.1 - 6.8 pmol/L)

Anti-Thyroidperoxidase abs 7.2 (<34 kIU/L)

Anti-Thyroglobulin Abs 19.1 (<115 kU/L)

I plan on getting my thyroid retested, but I am curious if anyone might explain the erratic T3 levels.

9 Replies

Your TSH clearly indicates Hypothyroid

TSH is being pushed out by pituarity to flog a failing thyroid

T4 is pushed out by the thyroid which then has to be converted into t3 elsewhere in the body however in order to do this levels of




Vit d3

Must all be halfway in the ranges

Catch 22 is hypothyroid trashes vitamins in the body so T3 lands up being low

Are you not being treated ? Have the above been tested


I did have all of those checked at one point and most were normal, only Vit D was a little low but supplementing it didn't seem to do much. I may order a large thyroid panel with those included next time.

I guess if it's a conversion issue, I was also thinking perhaps there's a pituitary tumour or something. I did have some abnormal bone growth at puberty.


When you say vit d 'didn't seem to do much' do you mean you didn't feel a difference or your levels didn't respond? If you're very deficient just taking a maintenance supplement won't help raise levels, you need a loading dose.

Are you taking thyroid hormone at the moment or are these diagnostic tests? Your tsh is rising as your t3 is falling, that is pretty unremarkable. Hormones fluctuate and respond to all kinds of conditions, what is more important than one isolated result is a trend. Do you feel unwell?


Hi, I've had heavy fatigue for a long time, my immune system is poor and I have some gut problems like food intolerances. It could be an autoimmune reaction to certain foods I guess, I wouldn't know how to get that diagnosed though.

I did take a high dose vitamin D & K2 supplement for a few months, I didn't feel any better at the time.

My TSH has been raised for at least a few months, I plan on testing it regularly along with free t3/t4.

I've just been struggling to find results like mine with normal free T4. From the answers I've had so far, vitamin deficiency seems to be the most common answer.


I don't know if there is a straightforward answer. It is unremarkable to have a raised tsh and other 'normal' Ts, it is called subclinical hypothyroidism and it happens all the time, which is why so many people struggle to get a diagnosis. Have you looked at 'can't get diagnosed' on the right of the page?

You may not feel better on more d. Your symptoms may be from your thyroid or something else. We continue to monitor our nutrient levels w blood testing because we may not feel when they are high or low, but it is thought to be better for your body and to better for using thyroid meds if levels are good. Low nutrients and low thyroid and whatever else is wrong can be death by a thousand cuts, one in isolation may not feel any different but accumulated it can mean the difference between feeling well and feeling unwell.


Thanks, I think I will order a comprehensive vitamin check at some point and tackle this problem from there.


It's not that common but it could be due to mild selenium deficiency. You could get your doctor to test for it or supplement in moderation. (The pituitary deiodinase is selenium based, so in cases of deficiency there will be less T3 and TSH will rise due to impaired T4 to T3 conversion in the pituitary).

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That's interesting, I haven't yet looked at my pituitary function.


Your pituitary itself looks very good and is responding appropriately to the lowish fT3.

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