• Also Known As:
  • Late-onset Male Hypogonadism
  • LOH
  • Testosterone Deficiency Syndrome
  • TD
  • Low T
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What is low testosterone?

Low testosterone, or low T as it is commonly called, generally refers to a condition in which a man does not produce enough testosterone. Testosterone is the main sex hormone (androgen) in men and is primarily produced by the testicles. It is responsible for male physical characteristics such as facial hair and muscle mass. Testosterone also helps maintain sex drive, sperm production, bone health, and red blood cell supply. Women also have testosterone but in much smaller amounts. This article focuses on the condition of low testosterone in adult men.

The brain and pituitary gland (a small gland at the base of the brain) control testosterone production by the testicles. Low testosterone can originate from testicular disease or failure (primary hypogonadism) or from disease or failure of the pituitary gland or hypothalamus (secondary hypogonadism).

Testosterone levels in men naturally decline starting around age 30. This is a normal part of aging and often doesn’t cause problems. Low T by itself is not a disease. Nor is a low T level by itself an indication to take testosterone by injection or by a patch. Laboratory testing and a clinical evaluation of signs and symptoms are both important components of diagnosing testosterone deficiency in adult men.

Besides aging, there are a wide variety of factors that can contribute to low testosterone. Some causes are related to conditions that arise later in life, like obesity. Others are related to conditions that people are born with, like Klinefelter syndrome, though these are much rarer. Some other causes of low testosterone include:

Treatment with testosterone replacement therapy can help relieve signs and symptoms of low testosterone. However, there are risks associated with treatment, and it may not be appropriate for every man with low testosterone.


About Low Testosterone

Signs and Symptoms

Low testosterone can produce a wide range of signs and symptoms that vary from man to man. Some symptoms are specifically linked to testosterone levels, such as:

  • Reduced body and facial hair
  • Very small testicles
  • Incomplete/delayed sexual development

Examples of symptoms that are suggestive of testosterone deficiency include:

  • Low sex drive
  • Erectile dysfunction
  • Decreased spontaneous erections
  • Enlarged breasts
  • Infertility

Other symptoms are non-specific and a variety of other conditions could cause them. Examples include:

  • Reduced lean muscle mass or bone mass
  • Symptoms of depression or changes in mood
  • Ongoing weakness or fatigue
  • Increased body fat, obesity
  • Irritability
  • Disturbed sleep
  • Decreased brain function, such as poor memory or focus


Diagnosing low testosterone begins with a history of an individual’s signs and symptoms, along with a physical exam, followed by laboratory tests to look at testosterone levels. The Endocrine Society and the American Urological Association recommend relying on both clinical examination and laboratory testing to diagnose low testosterone.

It is important to note that screening for low testosterone in men without signs and symptoms is not recommended.

Additional laboratory tests are used to determine the underlying cause of low testosterone and monitor individuals receiving testosterone replacement therapy.

Laboratory Tests

  • Testosterone level—this is the most important blood test for detecting low testosterone. Blood samples should be taken in the morning, after fasting, to help control for the daily variation in testosterone levels. Testosterone levels are typically sampled on at least two different days to confirm results. About 30% of men with an initial low testosterone result have normal levels after a repeated measurement. Testosterone is also measured to monitor treatment.About two-thirds of testosterone circulates in the blood bound to sex hormone binding globulin (SHBG) and slightly less than one-third bound to albumin. A small percent (less than 4%) circulates as free testosterone. The free plus the albumin-bound testosterone is the bioavailable fraction, which can act on target tissues. In many cases, measurement of total testosterone provides adequate information. However, in certain cases, for example when the level of SHBG is abnormal, a test for free or bioavailable testosterone may be performed as it may more accurately reflect the presence of a medical condition.Reference ranges for testosterone levels in adult men vary by age. (Levels naturally decrease as men age.) While accuracy of laboratory testing has significantly evolved over the past few decades, lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is why the reference range for testosterone is not provided here. It is important to use the range supplied by the laboratory that performed the test to evaluate whether results are “within normal limits.”It is also worthwhile recognizing that even in younger men, because the reference range is usually the central 95% of the results within a population, by definition, 2.5% of men will have a testosterone level below the lower limit of the reference interval. Another issue to consider is whether older men should have their own reference range for testosterone or should the reference range for men only be based on testosterone levels of men in 20’s or 30’s. In summary, men must consult their healthcare practitioner about the meaning of their testosterone test results.
  • Luteinizing hormone (LH) and follicle-stimulating hormone (FSH)—LH is a hormone that stimulates testosterone production and FSH is associated with sperm production. These tests are used together to help distinguish between low testosterone caused by a testicular problem from low testosterone caused by a problem originating in the pituitary gland or hypothalamus.When LH and FSH levels are high and testosterone is low, it indicates that the cause of low testosterone originates in the testicles. When LH and FSH is normal or low, it indicates that a pituitary problem underlies low testosterone. Normal LH and FSH are typically seen with age-related low testosterone.
  • Prolactin—prolactin is a pituitary hormone. It is tested if the pituitary gland is the suspected cause of low testosterone. High prolactin levels may indicate pituitary problems such as a tumor. High prolactin of any cause could interfere with normal testicular function.

Some tests may be done for men undergoing testosterone replacement therapy to monitor for side effects. Some examples include:

  • Hemoglobin—hemoglobin may be monitored for an increase in red blood cells (polycythemia). Polycythemia can be a side effect of testosterone replacement therapy and can lead to vascular problems like blood clots.
  • Lipid panel—to check for unhealthy lipid levels
  • PSA—to screen for prostate cancer

Non-Laboratory Tests

  • Magnetic resonance imaging (MRI) of the brain is sometimes used to check the pituitary gland and hypothalamus.
  • A bone mineral density Dexa-Scan (dual-energy X-ray absorptiometry or DXA) may be used to look for changes in bone density due to low testosterone.


Healthy lifestyle choices, including exercise, good nutrition, maintaining a healthy weight and avoiding excessive use of illicit drugs and/or alcohol, can help keep testosterone levels within a normal range. There are no known ways to prevent low testosterone linked to genetic conditions, testicular damage, or pituitary disorders.


Men diagnosed with low testosterone due to late-onset hypogonadism may be treated with testosterone replacement therapy to improve signs and symptoms.

The American Urological Association recommends prescribing treatment only to men who meet the clinical and laboratory definitions of low testosterone. And testosterone replacement therapy may not be appropriate for everyone with a diagnosis of low testosterone. For example, the Endocrine Society recommends against routine replacement therapy for men over 65 and suggests making individualized treatment decisions for aging men. Treatment may also be inappropriate for individuals with certain health problems, such as prostate cancer or sleep apnea.

Some of the benefits and risks of hormone replacement therapy remain unclear and are the subjects of active research. It is important for individuals diagnosed with low testosterone to talk to their healthcare practitioner about expectations for treatment and the potential side effects.

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