Difference between Free T3 and T3?: Hi After some... - Thyroid UK

Thyroid UK

111,260 members129,328 posts

Difference between Free T3 and T3?



After some great advice on here I paid to have medichecks tests done after I had received a low Free T4 blood result. I ordered the full thyroid and T3 tests. Although my Free T4 is still out of range (too low) medichecks reported that the results are normal and no further action needed.

I had an email from them this morning saying they were unable to do my T3 test and would I like a repeat test sent. I thought Id had the T3 checked but they told me I only had Free T3 checked and not T3. Can anyone explain the difference please?

Also I went to see my GP who refused to do anything regarding my low Free T4. A couple of days after I found out that a cousin of mine had recently been prescribed thyroxine and we have quite a history of thyroid problems in our family.

I am going to pursue this further and request some sort of treatment for the low Free T4. Wish me luck! My cousin lives 20 minutes down the road and was prescribed medication based on her symptoms and not blood results! It's madness!


14 Replies

T3 is triiodothyronine, the more active form of thyroid hormone. About 20% of T3 is secreted by the thyroid and the rest comes from deiodinase (conversion of T4 to T3) in healthy people. Most T3 (and T4) is bound to serum transport proteins, a small pecentage is 'free' and so available for use by thyroid hormone receptors. It is the 'free T3' that matters, the 'total T3' is of no use for diagnosing or treating hypothyroidism. So it's not worth the bother of following up the total T3 result.

It would help if you posted your TSH, fT3, fT4 results along with their reference intervals (numbers in brackets). I believe you are not taking thyroid hormone at the moment. If that's the case and you have symptoms along with a low fT4 then you are hypothyroid. The fact your TSH is not high suggests your pituitary is under performing a touch.

Vicm78 in reply to jimh111

Thank you for your very useful reply.

You have echoed what a lot of other people have said on here after I posted my results a little while ago.

I have tried to pursue the pituitary issue - lost a lot of blood after the birth of my son 4 years ago and others suggested I should investigate this. I had a follow up with a midwife a week ago who said my blood loss wasnt significant enough to cause a pituitary problem. I'm not so sure.

Like other people have advised - if my Free T4 is low and I am having symptoms then I should try to seek medication. My TSH sits in the normal range according to GP and Medichecks so that's prob why they aren't doing anything. Still have symptoms though!

Thanks again

jimh111 in reply to Vicm78

I doubt that you have a substantial pituitary problem from the blood loss but this is not the point. Your TSH can still be underperforming, we see a lot of these on the forum. The fact that your fT4 is below its lower limit and you have symptoms should be enough for your doctor to trial levothyroxine. I suspect you will need some liothyronine in the long term but they should at least trial levothyroxine for now. It's stupid, levothyroxine is cheap and safe, antidepressants are not. You are unable to work and a cheap, safe medication may solve the problem, they should prescribe. I would go back to your doctor and politely but firmly ask for a trial, say that your life is being ruined for the sake of a cheap medicine. If you do try to take someone with you for support. The endocrinologist seems useless, i'd drop them.

Vicm78 in reply to jimh111

My original results from GP were:

TSH: 1.41 Range 0.3-5.0

Free T4: 7.8 Range 7.9-16.0

My results from Medichecks were:

TSH: 2.31 Range 0.27 - 4.2

Free T4: 11.9 Range 12.0-22.0

Free T3: 4.5 Range 3.1-6.8

In both sets of tests my Free T4 is asterisked as low but GP said 'It's only 0.1 below the range so it's not low enough to worry about' but as I understand from other posters on here - even if my Free T4 was within range but at the lower end I could still be feeling pretty rubbish!

Clutter in reply to Vicm78


Sheehan's syndrome, also known as postpartum pituitary gland necrosis, is hypopituitarism (decreased functioning of the pituitary gland), caused by ischemic necrosis due to blood loss and hypovolemic shock during and after childbirth.


Low-normal TSH with below range FT4 indicates secondary/central hypothyroidism which is the result of insufficient production of bioactive TSH due to a pituitary or hypothalamic disorder.

Show your GP the NICE CKS cks.nice.org.uk/hypothyroid... which recommends patients suspected of having secondary/central hypothyroidism should be referred to endocrinology for investigation and management in case sex and growth hormones are also deficient.

Treatment of secondary/central hypothyroidism is Levothyroxine to raise FT4 and FT3 levels.

Vicm78 in reply to Clutter

Thank you. This is exactly the reason why I asked to see my maternity notes. I've felt awful since the birth of my son 4 years ago but they reckon a blood loss of 1300ml isn't enough to affect my pituitary. I'm not convinced. Always get sent away from GP being told I'm a recurrent depressive with anxiety.

I'm considering booking in to see a different GP and taking the evidence to them.

Your response and the articles are very useful and will help in my pursuit of treatment.

Clutter in reply to Vicm78


I would definitely see a different GP and even consider changing practice if you don't get better support. Your current GP really doesn't know what s/he is doing if s/he really thinks FT4 just a little bit below range isn't a problem.

Vicm78 in reply to Clutter

Thank you. I've seen and endo privately and had all manner of bloods done weeks ago but heard nothing despite chasing her.

So it's back to a different GP and I'm going to ask outright for medication. I'm sick of being told I have mental health issues and to take anti depressants.

Have been signed off work for 2 months and in that time the rest has done me wonders. I'm normally so exhausted.

Clutter in reply to Vicm78


I'd write to the private endo and say you expect a reply to your requests for your blood test results and ranges within 21 days or you will be contacting the GMC for assistance.

It's rare that GPs consider any form of hypothyroidism other than primary hypothyroidism which presents with high TSH and either low or normal FT4 and FT3. You must persist with trying to persuade your GP to consider secondary/central hypothyroidism and to prescribe Levothyroxine. If GP is unsure s/he should be able to consult with an endocrinologist via telephone.

In your blood, transport proteins exist that bind strongly but reversibly both T4 and T3. They hold about 99.98 and 99.8% of the total T4 and T3 in your body. Therefore if you measure total T4 and T3, you are measuring these and also the 0.02 and 0.2% of T4 and T3 that is not bound (ie free). But it is the free fractions that describe what your body cells are taking up, not the totals. The snag is that every indivudal has their own amounts of these transport proteins which can vary wildy in amount from person to person. So someone could have proteins that take up 4 times as much T4 and T3 as the average, and others who take up 30% or less. So you can get the same free T4 and T3 from greatly different reservoir sizes. That's why total T4 and total T3 can be misleading and lead to misdiagnosis.

Vicm78 in reply to diogenes

Thank you for your useful reply/explanation.

Vicm78: can I ask where you got your test done and how much it cost please?


You could consider changing to same GP as your cousin?

Have you had vitamin D, folate, ferritin and B12 tested?

Very common to be too low and affecting thyroid

What about thyroid antibodies tests?

Medichecks Dr blurb is just that, a generalisation. It's not an individual expert who knows the patient. It's just an approximate comment.

Prof Toft, past president of the British Thyroid Association and leading endocrinologist


I was thinking the same thing but ask if the doctor eith the good treatment is still there and make sure you are in their area before you ask to join. Don't want you to struggle to return if you aren't accepted.

You may also like...