Cortisol is a hormone produced by the adrenal glands that helps regulate metabolism and the stress response. High or low levels of cortisol can indicate adrenal dysfunction or other health problems.
Cortisol measured directly as a clinical lab marker reflects cortisol levels in the body.
References
Salvatore J. Azzopardi, et al.. Physiology, Cortisol - StatPearls - NCBI Bookshelf. StatPearls Publishing (2023). https://www.ncbi.nlm.nih.gov/books/NBK538239/Susan L. Everson, et al.. Relationship between Cortisol Responses to Stress and Personality. Psychosomatic Medicine (2006). https://www.nature.com/articles/1301012Mohammad H. Islam, et al.. Effect of increase in cortisol level due to stress in healthy young individuals: A systematic review. International Journal of Health Sciences (2019). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6371989/