Low testosterone can affect both men and women. Causes of low testosterone in males include undescended testicles and injury to the scrotum. Low testosterone in females includes ovary conditions. Treatment for low testosterone in men includes testosterone replacement therapy. Currently there is no FDA approved testosterone treatment for women.
Dr. Ben Wedro practices emergency medicine at Gundersen Clinic, a regional trauma center in La Crosse, Wisconsin. His background includes undergraduate and medical studies at the University of Alberta, a Family Practice internship at Queen's University in Kingston, Ontario and residency training in Emergency Medicine at the University of Oklahoma Health Sciences Center.
Ruchi Mathur, MD, FRCP(C) is an Attending Physician with the Division of Endocrinology, Diabetes and Metabolism and Associate Director of Clinical Research, Recruitment and Phenotyping with the Center for Androgen Related Disorders, Department of Obstetrics and Gynecology at Cedars-Sinai Medical Center.
Testosterone is produced by the testes in males and ovaries in females. The
testes are under the hormonal control of the hypothalamus and pituitary in the
brain and make testosterone in response to stimulation by FSH and LH.
Primary hypogonadism occurs because of the inability of the testes to
Causes of secondary and tertiary hypogonadism are due to a variety of
illnesses or diseases that affect the hypothalamus-pituitary-gonadal axis.
Symptoms of low testosterone depend upon when in the life cycle it occurs.
Osteoporosis and loss of muscle mass are significant complications of low testosterone.
In the United States, testosterone replacement therapy is available as an
FDA-approved treatment in men only. It may be administered by injection, patch
or gel, or gum and cheek putty.
What is testosterone?
Testosterone is an anabolic-androgenic steroid hormone which is made in the testes in males and in the ovaries in women (a minimal amount is also made in the adrenal glands). Testosterone has two major functions in the human body.
Testosterone is needed to form and maintain the male sex organs and promote secondary male sex characteristics (in both men and women) such as voice deepening and hair growth patterns. This function is related to its androgenic properties.
Testosterone is the facilitation of muscle growth as well as bone development and maintenance. This is a result of its anabolic properties.
Testosterone production is regulated by hormones released from the brain. The hypothalamus and pituitary gland located in the brain produce hormonal signals that ultimately result in the production of testosterone. The hypothalamus is located just above the brain stem, and among its many functions, it produces gonadotrophin releasing hormone (GRH). GRH travels a short distance to the pituitary gland located in the base of the brain stimulating the gland to release FSH (follicle stimulating hormone) and LH (luteinizing hormone). These hormones travel through the bloodstream to activate the sex organs in both men and women. Subsequently, these hormones also have a role in regulating testosterone levels in the bloodstream.
The majority of testosterone circulates in the blood bound to a carrier protein (a hormone is produced in one area of the body and has its effect on another area. Often a carrier protein is needed to assist the hormone's travel through the bloodstream). In this case the carrier protein is called "sex hormone binding globulin," or SHBG. When testosterone is being carried by SHBG, it is considered "bound". Bound testosterone does not play an active role in the body; only the unbound or "free" testosterone is able to enter the different cells of the body and exert its androgenic and anabolic effects. Thus, anything that affects the function or the amount of SHBG can also affect the total circulating amount of active testosterone.
Picture of the endocrine system including the testes and ovaries
What is low testosterone?
The human body functions within a relatively narrow range of normal; when chemicals such as hormones fall outside those normal levels, there can be consequences that affect the body at a cellular, organ, or systemic (body-wide) level.
Blood tests used to measure testosterone are usually performed in the morning. Testosterone sampling is difficult since the levels normally tend to bounce around a fair bit during the course of the day. The normal value for total testosterone in males is 270-1070 ng/dl. However, this depends to some extent on the individual laboratory being used, and the range can vary as a result. In women, there is debate about the accuracy of testosterone measurements, because the circulating values are so much lower than in males and are harder to accurately measure.
As people age, the amount of testosterone the body produces gradually falls in both men and women. Free testosterone levels can be measured and normal levels depend upon an individual's age.