Testosterone (See: Testosterone) is a male sex hormone that is found more in men and less in women. It is important for reproductive and sexual development in men. They belong to a class of hormones called androgens. Other functions of testosterone include a role in fat distribution in the body, muscle mass maintenance, and many others. Testosterone tests generally measure testosterone in free testosterone, bound testosterone, and bioavailable testosterone. While free testosterone accounts for only a small percentage of the total testosterone, bound testosterone is abundantly available. Bound testosterone is generally linked to certain protein molecules such as albumin and sex hormone binding globulin. Bioavailable testosterone is the sum of free testosterone and testosterone bound to albumin. Since bioavailable testosterone can be used by the cells of the body as it is readily available, it is important for men to have adequate amounts of it. Even though the total testosterone is the same, people might have different values of bioavailable testosterone leading to testosterone deficiency. People with low bioavailable testosterone tend to have symptoms of low testosterone and might require therapy. Reasons for reduction of bioavailable testosterone range from age, higher body mass index, and other conditions.