Testosterone
Also called T, androgen
Testosterone is a sex hormone made mainly by the testicles in men and, in much smaller amounts, by the ovaries in women. It is the main androgen, the group of hormones that drive male traits, and it helps control sex drive, muscle and bone growth, and the making of red blood cells in both sexes.
Most testosterone in the blood is bound to proteins, chiefly SHBG (sex hormone-binding globulin) and albumin. Only the unbound, or free, portion is readily available to tissues, which is why a lab report may list total and free testosterone separately.
Why it matters after 45
In men, testosterone usually declines gradually with age rather than dropping at a single point. Many men in midlife meet the term when tiredness, lower desire or changes in muscle and body fat prompt a blood test, and the result has to be read against the time of day it was drawn and the SHBG level. Women make testosterone too, in much smaller amounts.
Where it comes up
References
- Cleveland Clinic. Testosterone. https://my.clevelandclinic.org/health/articles/24101-testosterone
- MedlinePlus. Testosterone Levels Test. U.S. National Library of Medicine. https://medlineplus.gov/lab-tests/testosterone-levels-test/
- MedlinePlus. Aging Changes in Hormone Production. U.S. National Library of Medicine. https://medlineplus.gov/ency/article/004000.htm
Definitions here are educational and are not medical advice. They explain what a term means; the pages linked above cover what it means for you, and a clinician reviews your own results. Editorial & medical review policy · All glossary terms