What is T3 and T4?

[Rona_1968]

Hi!! I've been diagnosed wjth hypothyroidism for 11 yrs now and currently on 125mcg of levothyroxine. I've been reading different posts and people have been talking about T3 and T4, is this tested when you have your annual blood test at the doctors? Thankyou !!

[Hidden]

I don't know how these things work in the UK, but in Belgium, only the TSH and FT4 levels are routinely measured. Only the so called alternative doctors will test your FT3 levels as well.

T4 is an inactive storage hormone that needs to be converted to T3 (which is the truly active thyroid hormone). A healthy thyroid gland produces small amounts of T3; about 90% of what it produces is T4, and the idea is that enough T4 is then converted to T3 in order to achieve optimal T4 and T3 levels.

However, in many hypothyroid people, this process does not work optimally. Many are poor converters, meaning they can take a lot of T4, yet suffer from insufficient T4 to T3 conversion. These people remain hypothyroid, although most doctors seem to think they are optimally treated because their TSH and FT4 levels are in range.

Some people, though, seem fine on T4 only drugs, which means they are converting enough T4 to T3.

So while it's not true that everyone feels better on both T3 and T4, I am always surprised to see how many thyroid patients actually do...unfortunately, it's a constant battle with ignorant doctors.

[shaws Administrator]

Usually in the UK the TSH and T4 are the only ones to be measured. Sometimes the TSH alone.

If you were diagnosed 11 years ago, how do you feel at present. I see you are on levothyroxine alone and what dose are you taking?

T4 is the inactive hormone which converts to T3. T3 is the Active hormone required in all of our receptor cells, the brain contains the most. That's why we mention quite often about T3 or Free T3 because if it is too low we don't feel so good. Not many labs do these unless requested by GP and GPs aren't always knowledgeable about the action of thyroid hormones or why patient complains when they appear to be on a decent dose.

[Rona_1968 in reply to shaws]

I take 125mcg of levothyroxine daily. I find it hard to keep at a stable weight and im about stone overweight. I get tired easily and joints ache but put this down to my age, 48. I retain water in my legs . I feel cold in the day but wake up sweating abd hot at night. Dont know whether this is the start of the menopause or my thyroid. 😞

[shaws Administrator in reply to Rona_1968]

New research has shown that many feel an improvement when they add T3 to T4. More than one Research Team has shown that combo to be more effective for many. I know T3 is not being prescribed at present, and I don't know if you can afford your own to have a trial.

The aim of thyroid hormone replacement is to get rid of all clinical symptoms and many cannot do this on levo only, so that's why they add T3 or switch to NDT.

Make a new appointment for a blood test, the very earliest possible, fasting (you can drink water) and allow 24 hours gap between last dose and the test and take afterwards. Ask GP for a Full Thyroid Function Test and if or lab wont do so (some wont if TSH is in range) you can get your own through one of our recommended labs. You need:

TSH, T4, T3, Free T4, Free T3. If you've not had these recently request them, B12, Vit D, iron, ferritin and folate. Deficiencies of these can also cause unpleasant symptoms.

Get a print-out with the ranges and post on a new question for comments. We can get well and you, theoretically should feel well with no symptoms.

[Hapyjackie]

GPs only test TSH and that's often where the problems start! I am awaiting an appointment with an endocrinologist so I will be asking if they do a full and more meaningful test. I'll let you know!

[Marz in reply to Hapyjackie]

Probably best to have Home Testing kits and have the tests done you need to enable you to have OPTIMAL health. Deatails on the main website - thyroiduk.org

That way you can take control of your health. After many years on this forum it us rare to find an Endo that knows his stuff ....

Good Luck 😊

[Rona_1968 in reply to Marz]

Thankyou I'll check the site out ☺

[Rona_1968 in reply to Hapyjackie]

Yes interesting, goodluck with your blood test ☺

[Rona_1968]

Thankyou very much helpful advise, i'm due a blood test so will keep it all in mind .☺