Total testosterone refers to the sum of the concentrations of protein-bound and unbound testosterone in the circulation and can be broken down into three categories:[1]
- Tightly bound testosterone: About two-thirds of testosterone in the blood is bound to sex hormone binding globulin. It is not readily available for use by the body.
- Loosely bound testosterone: About one-third of testosterone in the blood is weakly bound to albumin. Once the bond is broken, the testosterone circulates as free testosterone in the body.
- Free testosterone: A small percentage of testosterone in the blood floats around freely. The body can readily use it, and the enzyme 5-alpha-reductase can convert it to DHT. The term bioavailable testosterone refers to the sum of loosely bound and free testosterone.
Assessing testosterone levels
