Testes-Based Conditions
Men whose testosterone deficiency is caused by an abnormality in the testes often display increased FSH levels, increased LH levels, and impaired sperm production. These conditions include:

• Trauma — A direct physical injury to the testes may damage the cells that produce testosterone.

• Castration — Surgical removal of the testes, e.g., for testicular cancer, results in severe reduction in testosterone production.

• Orchitis — Testicular inflammation can occur after a post-puberty bout with the mumps (there is a higher risk of risk of infertility than low testosterone).

• Radiation treatment or chemotherapy — These therapies for other diseases may damage the testosterone-producing cells of the testes.

• Testicular tumors — Treatment of testicular tumors may directly affect testosterone production.

• Pituitary tumors   The growth of abnormal tissue in the pituitary can disrupt the gland's normal functioning and interfere with hormone production. Some tumors produce hormones that can interfere with LH production.

• >High prolactin levels   High levels of the pituitary hormone prolactin from a hypothalamic or pituitary tumor, certain medications, and other causes inhibit LH and FSH production, resulting in low testosterone levels.

• Medications — Certain drugs used to treat medical conditions that affect the brain (e.g., opiate pain medications such as morphine) and hormones (e.g., cortisone-like medications such as prednisone, and anabolic steroids) may inhibit LH and FSH secretion by the pituitary, and in turn, testosterone production by the testes.

• HIV/AIDS — Viruses or other infectious agents may directly or indirectly affect the hypothalamus, pituitary or testes and can decrease testosterone levels; as many as 50 percent of men infected with the human immunodeficiency virus (HIV) may have low testosterone. Severe malnutrition that occurs with AIDS and other wasting conditions may also inhibit LH and FSH production, resulting in low testosterone levels.

• Immune and Inflammatory Pituitary Disease — Conditions such as sarcoidosis, tuberculosis, fungal infection, and autoimmune disease may also impair the pituitary's ability to make hormones.

• Klinefelter's syndrome — A genetic condition in which an extra X chromosome is present (about one in every 400 men have this); testosterone production is low to low normal; men with this syndrome also may have markedly reduced bone density and learning disabilities.

• Hemochromatosis — A common genetic disorder in which there is excessive depositing of iron into body tissues, most notably the liver, pancreas, heart, skin, and pituitary gland, resulting in reduced functioning of these organs. Iron deposition in the pituitary gland causes impaired production of LH and FSH, which results in decreased testosterone production.

• Kallmann's syndrome — Usually a recessive genetic disorder associated with the X chromosome, which occurs in about one of every 10,000 men. A deficiency of gonadotropin releasing hormone (GnRH) impairs the release of LH and FSH, which decreases testosterone production; men with the syndrome lack the sense of smell; testes do not enlarge at puberty.

• Prader-Willi syndrome — A genetic disorder characterized by decreased muscle tone in infancy that improves with age, underdeveloped genitals (including undescended testes in boys) and low sex hormone levels. An obsession with food and compulsive eating, also linked with this disorder, may begin before the age of six.

• Myotonic dystrophy — The most common adult form of muscular dystrophy, this genetic condition only occurs in men and is carried on the Y chromosome; because testicular failure usually occurs around the age of 30 to 40, men may have sons at risk for the disease.

Importance of the Medical History
Sometimes physical symptoms can suggest a medical problem. For example, a man who, as he ages, has a progressive decrease in muscle mass, loss of libido, erectile dysfunction (ED) or reduced sperm count may have low testosterone. Similarly, a teenager who still has the appearance of a young boy — small testes, penis and prostate; scant pubic and body hair; and a high-pitched voice — shows clear signs of someone with inadequate testicular function. There are cases, though, that may involve some medical detective work. Therefore, it is extremely important to provide the doctor with a detailed medical history. Things that should be discussed include:

• past or present major illnesses;
• all prescription and nonprescription drugs currently being taken;
• family/relationship problems, such as sexual problems; and
• any major life events or changes that have occurred.

Physical Examination
During the physical examination, the doctor will look at:

• the amount and distribution of body hair;
• presence and degree of breast enlargement;
• size and consistency of the testes;
• abnormalities in the scrotum;
• size of the penis; and
• the ability to see in all directions (visual field test)

Testosterone circulates in the blood in three forms:

• About 40 percent of testosterone is bound tightly to a protein called sex hormone binding globulin (SHBG), and is not available to body tissues for action;
• About 58 percent is weakly bound to another protein called albumin and is available to many tissues for action;
• About two percent circulates freely in the bloodstream.

Other Tests

• Because low testosterone levels may affect bone mass, the doctor may want to assess any bone loss with bone density testing.
• Genetic testing can confirm the presence of an inherited condition.
• If tests cause the doctor to suspect a problem within the pituitary gland, he/she may want to examine the gland to see if a tumor is present. Two examination procedures are most common, and neither penetrates the skin. A computed tomography, or CT, is a computer-assisted X-ray process. Magnetic resonance imaging, or MRI, uses a combination of radio waves, high intensity magnetic fields, and computer technology to produce images of the body's interior. The MRI is often the preferred procedure; both tests are usually done before and after a minute amount of dye is injected into a vein.