Free testosterone
The active, unbound fraction of testosterone. Often elevated in PMOS even when total testosterone reads normal.
Most of the testosterone in the bloodstream is bound to a protein called SHBG, which holds it inactive. The small fraction that is not bound is free testosterone, and it is the part that actually reaches tissues like the skin, hair follicles, and ovary to do its work.
Total testosterone is the bound plus the free. In PMOS, insulin lowers SHBG, so more testosterone comes loose. The result is that free testosterone can be elevated even when total testosterone looks completely normal on a lab report.
This is why "your testosterone is normal" can sit next to clear androgenic symptoms. The free androgen index (FAI), a calculation from total testosterone and SHBG, is another way to estimate the same thing. If you have androgenic signs with a normal total testosterone, free testosterone or FAI is worth asking about by name; they are not on every standard panel.