Cortisol
Also written as: Serum cortisol, AM cortisol
The body's main stress hormone, made by the adrenal glands on a strong daily rhythm.
What it measures
The amount of cortisol, a steroid hormone made by the adrenal glands, circulating in the blood at the moment of the draw. Cortisol follows a strong daily rhythm - highest shortly after waking and lowest around midnight - so a level only makes sense alongside the time it was taken.
Why a doctor orders it
Ordered when a clinician is considering conditions of too much or too little adrenal hormone output, or as part of a work-up for unexplained fatigue, weight change, or blood pressure changes. A single blood level is usually a starting point that leads to more specialized timed testing rather than a final answer on its own.
What is generally associated with a higher result
Broadly associated with overactivity of the adrenal glands or the signals that drive them, but also with ordinary physical or emotional stress, acute illness, pregnancy, and estrogen-containing medications, all of which can raise cortisol without any adrenal disease.
What is generally associated with a lower result
Broadly associated with underactive adrenal glands or reduced pituitary signaling, and also with recent or current use of steroid medications, which quiet the body's own production. Levels drawn later in the day are naturally much lower.
Everyday things that move this number
Not every shift in a value reflects disease. These are ordinary factors known to affect this particular measurement:
- Time of day of the blood draw, since cortisol is naturally highest in the morning
- Stress, including anxiety about the blood draw itself
- Steroid medications in any form, including creams and inhalers
- Estrogen-containing medications such as birth control pills
- Shift work, poor sleep, and pregnancy
Questions to take to your appointment
- Was this drawn at the right time of day for the question being asked?
- Could any steroid medicine I use, even a cream or inhaler, have affected this?
- Would a timed or stimulation test give a clearer picture than a single level?
Build a printable questionnaire with your own results →
Where to read more
MedlinePlus, from the US National Library of Medicine, publishes patient-facing pages on individual lab tests and is a reliable next stop: medlineplus.gov/lab-tests .
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