The pituitary gland in your brain controls the amount of testosterone your body makes.
Most of the testosterone in your blood attaches to 2 proteins: albumin and sex hormone binding globulin (SHBG). Some testosterone is not attached to proteins, or free. Free testosterone and albumin-bound testosterone are also referred to as bioavailable testosterone. This is the testosterone that is easily used by your body.
If your healthcare provider thinks that you have low or high testosterone, he or she will first test total testosterone levels. This looks at all 3 types of testosterone. The free testosterone can help give more information when total testosterone is low.