T Nation

Free Testosterone vs Total T


#1

Which is more important for analyzing if you are normal or not, free testosterone or total testosterone? I would assume TT, but my doc says he cares about FT more than TT. I tend to have decent FT even if my TT is low. Very curious if my doc is correct or not.


#2

Bioavailable testosterone, which corresponds to the biologically active testosterone ( free testosterone and testosterone bound to albumin ).

Testosterone bound to SHBG is inactive.


#3

With normal guys, not on TRT, and more so when younger, FT is released in pulses with a short half-life. So any given lab is a snapshot of something that is moving. TT is often a better indicator. So testing both is important. There can be some wrinkles with high or low SHBG that affect the amount of T+SHBG that is floating around affecting TT scores.


#4

Thank you both very much for your responses.


#5

We do see some docs who do not understand the fine details and will look at FT or TT and see one in range and say the normal word and not take action. Your doc does understand the importance of FT, but may not be considering how FT fluctuates. When on TRT, FT is steady, but will rise and fall with weekly injections. FT is very steady with injections EOD. E2D, E3.5D, so FT labs results then are a real good indication of overall status. But overall status really must consider FT and E2.


#6

Would you say then that, on TRT, if the doctor is checking FT and E2, but not TT, that will still be a fine way to measure it's success?