Cortisol is the main glucocorticoid of the adrenal cortex, released under pituitary ACTH control, and it governs glucose supply, blood pressure and the response to stress. Serum cortisol captures a single moment in a hormone that changes hour by hour. It speaks for the hypothalamic-pituitary-adrenal axis rather than for stress in the everyday sense.
No readings for this marker yet.
Persistently high morning values most often point towards Cushing's syndrome, and also rise with acute illness and pain, which drive genuine hormone output, and with pregnancy and estrogen-containing contraceptives, which raise the binding protein. Low values raise the question of adrenal insufficiency or of pituitary failure, and they are expected in anyone taking glucocorticoids, which suppress the axis. Neither direction is settled by one draw; dynamic testing under a doctor's direction is what distinguishes them.
Timing dominates everything: secretion peaks shortly after waking and falls through the day, so the sample is drawn in the morning at a recorded hour, and shift work or a disturbed night invalidates the comparison. Recent illness, surgery, alcohol and inhaled or topical steroids all shift the result. It is interpreted alongside ACTH, and DHEA-S is added when a broader picture of adrenal output is wanted.
Reference ranges are general adult values and depend on lab, assay, age and sex. For orientation, not diagnosis — discuss results with your doctor.