Total Testosterone

Testosterone is the primary androgen hormone, produced mainly in the testes in men and in smaller amounts by the ovaries and adrenal glands in women. It plays critical roles far beyond reproductive function — it is essential for maintaining muscle mass, bone density, red blood cell production, cognitive function, mood, and cardiovascular health in both sexes.

In men, total testosterone declines approximately 1–2% per year after age 30, a process sometimes called 'andropause.' By age 50, many men have levels that would have been considered deficient at age 25. This decline is associated with increased visceral fat, loss of lean muscle (sarcopenia), decreased bone density, depression, reduced libido, and increased cardiovascular and metabolic risk. The relationship between low testosterone and mortality has been demonstrated in multiple large cohort studies.

However, interpreting testosterone levels requires nuance. Total testosterone includes both bound (to SHBG and albumin) and free (bioavailable) fractions. A man with high SHBG (common in aging, liver disease, and hyperthyroidism) may have adequate total testosterone but low free testosterone — the fraction that actually exerts biological effects. For this reason, free testosterone or bioavailable testosterone should be assessed alongside total levels. In women, testosterone is important for libido, energy, bone health, and muscle maintenance, though at much lower levels than in men.