Low testosterone (or "low T") is a condition in which the body is unable to produce normal amounts of the hormone testosterone. It causes different symptoms depending on age and when the condition develops. You can be born with low testosterone or it can develop later in life.
Testosterone is the main androgen, a group of sex hormones that help start puberty. Testosterone plays a role in reproductive health and is necessary for sperm production. It’s also involved in the development of muscle mass and bone density.
The symptoms of low testosterone in males depend on the cause of the low level and the age at which it occurs.
Levels of the hormone are naturally much higher in people assigned male at birth (AMAB) than in people assigned female at birth (AFAB), but low testosterone can also occur in women.
No matter what the cause, symptoms alone are not enough for a diagnosis of low testosterone: A blood test is needed to confirm that a testosterone level is, indeed, low.
Low testosterone in men — male hypogonadism — can occur at any age, as a result of problems affecting the testicles or the pituitary gland. It affects children, adolescents, and adults differently.
Signs of hypogonadism in an infant include:
Ambiguous genitalia
Female genitalia (in a genetically male child)
Underdeveloped male genitalia
In boys, hypogonadism is associated with delayed puberty and can cause symptoms such as:
Lack of development of muscle mass
No deepening of the voice or growth of body hair
Slow increase in size of penis or testicles
Arms and legs that grow out of proportion to the rest of the body
Not all men with age-related low testosterone have — or are bothered by — symptoms. In addition, the level at which symptoms occur varies from man to man.
According to the Endocrine Society, testosterone levels naturally decrease by 1 percent each year after age 30, though don’t severely deplete, even in advanced age. Normal T levels in adult men should be between 300–1,000 nanograms per deciliter, depending on age and the lab that’s used for testing.
Nonspecific signs and symptoms such as fatigue, sleep problems, and low mood can also be caused by other factors such as medication side effects, depression, and excessive alcohol use.
Women and people assigned female at birth also produce testosterone — in the ovaries and adrenal glands — and need the hormone, but at much lower levels than men. They also experience a normal drop in testosterone levels as they age and in the time leading up to menopause. By the time women reach menopause, their testosterone levels may be half of what they were, according to Cleveland Clinic. Women with a loss of pituitary function (hypopituitarism), loss of adrenal function (Addison’s disease), or surgical menopause (removal of the ovaries), can experience a decline in androgen production that can become symptomatic.
A drop in testosterone in women may be associated with:
Low testosterone in women can be difficult to diagnose because a direct correlation between symptoms and low T has not been established, and there is a lack of accurate tests for androgen levels and valid reference ranges for women.
The complications that can arise if low testosterone isn’t treated depend on when the condition develops.
During fetal development, low T can cause ambiguous genitalia. In adolescence, it can lead to delayed puberty. In adult men, it can cause infertility, erectile dysfunction, and osteoporosis.
If you’re experiencing signs and symptoms of low testosterone mentioned above, talk to a healthcare provider. Your doctor will ask about your symptoms and evaluate you, and may order blood tests or refer you to an endocrinologist or urologist.
If your child was assigned male at birth and isn’t showing signs of puberty by the age of 14, talk to their pediatrician, notes Cleveland Clinic.
Hypogonadism and age-related low testosterone are diagnosed with blood tests that measure the level of testosterone in the body.
The Endocrine Society and the American Association of Clinical Endocrinologists recommend testing for suspected low T with a total testosterone test performed in the morning (when testosterone levels tend to be highest in young men, although this isn't necessarily the case in older men). The blood test should be done after an overnight fast.
The test is often repeated on another day if the results show a low T level.
The majority of testosterone in the blood is bound to one of two types of protein — either albumin or sex hormone binding globulin (SHBG) — while a small percentage is unbound, or free.
The portion of testosterone that is bound to SHBG is biologically inactive but, because the bonds between testosterone and albumin are weaker than those between testosterone and SHBG, the portion bound to albumin is biologically active. Bioavailable testosterone therefore includes free testosterone and albumin-bound testosterone.
A total testosterone test, the most common type of test, measures free testosterone and testosterone that's attached to proteins. A free testosterone test, which is less common, measures only the biologically active form of testosterone. This test is less common, as is a bioavailable testosterone test which measures free testosterone and testosterone that's loosely attached to a blood protein called albumin.
A number of medical conditions and medications can raise or lower the amount of SHBG in the blood, consequently altering the amount of bioavailable testosterone. Conditions that can raise levels of SHBG can be related to liver disease, hyperthyroidism, and reduced production of sex hormones (in males). Low levels of SHBG may be related to hypothyroidism, type 2 diabetes, obesity, and polycystic ovary syndrome (in females). In those situations, measuring the amount of bioavailable testosterone gives a more accurate indication of the amount of biologically active testosterone in a person's system.
Other blood tests you may be given to diagnose low testosterone include:
Luteinizing hormone (LH) blood test can help determine if an issue with your pituitary gland is causing low testosterone.
Prolactin blood test measures levels of prolactin, a hormone responsible for lactation. High levels may be a sign of pituitary gland issues or tumors.
Iron level test is used to rule out hemochromatosis, a disorder in which extra iron builds up in the body, causing symptoms like fatigue, joint pain, loss of interest in sex or erectile dysfunction.
Low testosterone (low T) affects important body functions and presents various symptoms depending on your age. Males and females each experience low testosterone differently, from muscle loss and low sex drive to fatigue and mood changes. If these symptoms sound familiar, consider talking to your doctor to check your testosterone levels.
