Testosterone is a steroid hormone and a sex hormone primarily produced in the testicles of men and the ovaries of women and in small amounts by the adrenal gland in both genders. This hormone is the principal steroid that repairs and regenerates healthy tissues, attributing to muscle growth. 

Testosterone facilitates the development of male secondary sexual characteristics and reproductive tissue, including increased bone and muscle mass and hair growth. Healthy levels of testosterone are needed for general health and well-being, as research has shown the relationship between decreased levels and age-related diseases like osteoporosis, heart disease, diabetes and decreased sex drive.

There are two types of testosterone: free and bound. Free testosterone is that which is not bound to the sex hormone binding globulin (SHBG) glucoprotein but is freely floating in the blood stream. Bound testosterone is considered neutral—and somewhat unusable. Total testosterone includes both types. It is important to keep the levels of testosterone and estrogen balanced, and the testosterone free and total blood test can help you do just that.