Most people think of testosterone as the male hormone, because men typically have much higher levels of the hormone than women.1 However, as men age, their testosterone levels begin to decline. This process can be a normal part of getting older, but it may also be the result of a medical condition called hypogonadism or andropause.

Low testosterone levels are more than just an inconvenience. Hypogonadism can cause sexual dysfunction and lead to health problems, such as osteoporosis and depression.

Low serum testosterone levels affect approximately 40% of men aged older than 45 years, and more men develop the condition as they age — approximately half of men aged 80 years and older have low testosterone,2 according to the American Urological Association. The first step in recommending treatment options for patients with low testosterone is properly identifying the condition.

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Slow changes to the body, including reduced body hair and decreased prostate size are symptoms of low testosterone, according to the American Association of Clinical Endocrinologist’s (AACE) medical guidelines for evaluating and treating hypogonadism.

In other men, low testosterone levels may prevent hair loss. Infertility is also associated with the condition; therefore, it is not uncommon to make the diagnosis during an infertility workup.3


Two main areas of the body affect testosterone levels: the testicles, and the pituitary gland and nearby hypothalamus.4 The testicles actually produce testosterone, whereas the hypothalamus and pituitary gland send chemical signals to regulate production.

Low testosterone levels can result from a problem in either region. Low testosterone that originates in the testicles is called primary hypogonadism, whereas those cases caused by a malfunctioning pituitary gland or hypothalamus are referred to as secondary hypogonadism.

Men may inherit a trait that causes problems with testosterone production, or the condition may be triggered by an infection or injury.

Common causes of primary hypogonadism are:

  • Testicular injury
  • A mumps orchitis infection affecting the testicles
  • Undescended testicles
  • Hemochromatosis
  • Radiation or chemotherapy

Secondary hypogonadism may result from:

  • Abnormal hypothalamic development due to Kallmann syndrome
  • A pituitary tumor or disorder
  • Sarcoidosis, tuberculosis or another inflammatory disease
  • HIV or AIDS
  • Opiate use
  • Obesity

In addition to the above risk factors, men with type 2 diabetes have twice the risk of hypogonadism than the average man.5

In some cases, low testosterone might be a normal side effect of aging. Clinicians have differing opinions about what testosterone levels should prompt intervention.4

When a man’s testosterone levels are too low, it affects not only his sex drive and sperm function but may also have implications for bone health, red blood cell production and the development and distribution of muscle and fat.4

Common side effects associated with low testosterone include:6

  • Anemia
  • Fatigue
  • Depressed mood
  • Reduced strength
  • Cognitive problems
  • Hot flashes

Making the diagnosis

Once physical symptoms of low testosterone are identified, labs to measure total testosterone levels should be performed to confirm the diagnosis. The AACE defines the normal range for testosterone as between 300 to 1,000 ng/dL. Anything below that range is considered low. Blood tests should be performed in the morning, when testosterone levels are typically highest.3