Most testosterone in the blood is bound to SHBG and albumin; only the small unbound (“free”) fraction is readily available to tissues. Free testosterone can better reflect androgen status than total testosterone, especially when SHBG is abnormal. It is usually estimated from total testosterone, SHBG, and albumin rather than measured directly.
Related terms
- SHBG
- A blood protein that binds sex hormones; high SHBG lowers usable (free) testosterone.
- TRT
- Prescription testosterone (gel, injection, or pellet) for men with clinically low, symptomatic levels.
- Hypogonadism
- Clinically low testosterone plus symptoms — diagnosed by blood tests, not symptoms alone.