Why Test For Free T4 and not Free T3?

[Gsp177]

Why is it the NHS will test for Free T4 and not Free T3 which is the active hormone our bodies use?

[Clutter]

GSP, FT3 is a more expensive and complicated test. NHS do test for it, but labs often decline to test it unless TSH is suppressed.

[Heloise]

and if your T4 is low, it is assumed your FT3 will also be low. Unfortunately if your FT4 is high, I guess they assume wrongly that your FT3 will also be high enough.

[Hidden]

I was tested for TSH and FT4 by my GP and referred to an endocrinologist. I thought he would test antibodies and FT3 but NO! He asked a few questions did the same test as GP then declared I have no endocrin problems!

What a waste of time

[Gsp177]

Thanks everyone, is frustrating. Rather than add to this thread I've created another one, which explains the situation I'm in. Be grateful of your thoughts?

healthunlocked.com/thyroidu...

[shaws Administrator]

It is more expensive and I think they need to review their practices in the treatment of thyroid dysfunction. The are so fixed on the TSH which is from the pituatary gland anyway and doesn't always function as they imagine it should do. The should learn and acknowledge symptoms and take a family history and personal medical history.

[PR4NOW]

Don't forget that the FT3 test is the most problematic of all the TFTs as far as variance of results. PR

[helvella Administrator Thyroid UK in reply to PR4NOW]

Quite so, PR,

And if you believe in a nice simple relationship between TSH and thyroid hormone adequacy, then TSH does indeed make sense.

It is when you try to use TSH on its own and without proper evaluation of pituitary and/or hypothalamus issues, of conversion issues, of set points, etc., then you come a cropper. Or, unfortunately, the patients do.

In some niches it is well known and accepted that TSH does not work "as advertised". One is after a period of TSH suppression such as when a total thyroidectomy is performed on someone who has been hyperthyroid with Graves for a long time. Can take a very long time for TSH to creep up again.

Rod