T3 and t4

[Pippydoodles]

Hi all,

Just a quick question to hopefully clarify something for me as I'm quite new to this, when people talk about FT3 and FT4 is that the same as T3 and T4?

Thanks and hope every everyone is feeling OK today xx

[diogenes Remembering]

No they are quite different though loosely related. T3 and T4 refer to the total hormones in your blood. On the average, 99.98% of the T4 and 99.8% of the T3 are bound onto circulating transport proteins. This leaves 0.02 and 0.2% respectively for FT4 and FT3, which are the active part of the hormones readily available to the cells. The problem is that we all have different amounts of transport proteins and a minority of us have them so different from the average that they carry far more (or far less) T4 and T3 than the average, yet produce the same FT4 and FT3. So FT4 and FT3 measure the immediately useful hormone available to the cells, and T4 and T3 the sum of the protein bound and free hormones. The former measurements are the most accurate and useful, especially if you are not average.

[Pippydoodles in reply to diogenes]

That's so helpful - thank you xx