late-onset hypogonadism late-onset hypogonadism late-onset hypogonadism (loh) or testosterone deficiency syndrome (tds) is a condition in older men characterized by measurably low testosterone levels and clinical symptoms mostly of a sexual nature, including decreased desire for sex, fewer spontaneous erections, and erectile dysfunction. it is the result of a gradual drop in testosterone; a steady decline in testosterone levels of about 1% per year can happen and is well documented in both men and women. late-onset hypogonadismspecialtyendocrinology signs and symptoms some men present with the symptoms, but with normal testosterone levels, and some men with low testosterone levels have no symptoms; the reasons for this are not known. some men in their late 40s and early 50s develop depression, loss of libido, erectile dysfunction, and other physical and emotional symptoms such as irritability, loss of muscle mass and reduced ability to exercise, weight gain, lack of energy, difficulty sleeping, or poor concentration; many of these symptoms may arise from a midlife crisis or as the results of a long-term unhealthy lifestyle (smoking, excess drinking, overeating, lack of exercise) and may be best addressed by lifestyle changes, therapy, or antidepressants. causes testosterone levels are well-documented to decline with aging at about 1% per year in both men and women after a certain age; the causes are not well understood. diagnosis as of 2016, the international society for the study of the aging male defines late-onset hypogonadism as a series of symptoms in older adults related to testosterone deficiency that combines features of both primary and secondary hypogonadism; the european male aging study (a prospective study of ~3000 men) defined the condition by the presence of at least three sexual symptoms (e.g. reduced libido, reduced spontaneous erections, and erectile dysfunction) and total testosterone concentrations less than 11 nmol/l (3.2 ng/ml) and free testosterone concentrations less than 220 pmol/l (64 pg/ml). if a person has symptoms of late-onset hypogonadism, testosterone is measured by taking blood in the morning on at least two days; while immunoassays are commonly used, mass spectrometry is more accurate and is becoming more widely available. the meaning of the measurement is different depending on many factors that affect how testosterone is made and how it is carried in the blood. increased concentrations of proteins that bind testosterone in blood occur if the person is older, has hyperthyroidism or liver disease, or is taking anticonvulsant drugs (which are increasingly used for depression and various neuropathies), and decreased concentrations of proteins that bind testosterone occur if the person is obese, has diabetes, has hypothyroidism, has liver disease, or is taking glucocorticoids or androgens, or progestins. if levels are low, conditions that cause primary and secondary hypogonadism need to be ruled out. screening due to difficulty and expense of testing, and the ambiguity of the results, screening is not recommended. while some clinical instruments (standard surveys) had been developed as of 2016, their specificity was too low to be useful clinically. management