What is Low T (hypogonadism)?
Hypogonadism, or Low T, is a medical condition in which the testes produce abnormally low levels of testosterone, typically diagnosed when serum testosterone falls below 300 ng/dL.
Hypogonadism, commonly called Low T, occurs when the body fails to produce adequate amounts of testosterone. This hormone plays a central role in male sexual function, muscle development, bone density, mood regulation, and energy levels. The condition can develop at any age but becomes increasingly common in older men.
Clinical diagnosis relies on laboratory measurement of serum testosterone. Most practitioners use a threshold of 300 nanograms per deciliter (ng/dL) as the lower boundary of normal, though some guidelines reference 250 ng/dL. A single low reading may prompt repeat testing to confirm diagnosis, since testosterone levels fluctuate naturally throughout the day and across seasons.
Men with hypogonadism frequently report reduced sexual desire and erectile dysfunction. Other symptoms include fatigue, decreased muscle mass, increased body fat, mood disturbances, and cognitive changes. Bone density may decline, raising fracture risk. Not all men with Low T experience symptoms, making blood work essential for accurate diagnosis.
Two main categories exist: primary hypogonadism (testicular failure) and secondary hypogonadism (insufficient hormonal signaling from the pituitary or hypothalamus). Causes range from age-related decline to injury, medication effects, obesity, or endocrine disorders. Men's health providers can evaluate underlying causes through additional testing and determine whether testosterone replacement therapy or other treatment approaches are appropriate.