Cortisol
Also called: Hydrocortisone
Cortisol is the body's primary stress hormone. Both excess and deficiency cause distinct, recognisable clinical syndromes — interpretation is time-of-day dependent.
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Range source: MedlinePlus — Cortisol blood test, checked Oct 31, 2026
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What does Cortisol measure?
Cortisol is the adrenal cortex's main glucocorticoid. It mobilises glucose, suppresses inflammation, supports blood pressure and maintains alertness. Release follows a strong diurnal rhythm: peak in early morning (around 8 AM), nadir around midnight. A single blood draw must be interpreted in that context — a "normal" 8 PM cortisol of 18 µg/dL would suggest Cushing's syndrome, while the same value at 8 AM is unremarkable. Salivary cortisol at midnight and 24-hour urinary free cortisol are more specific screening tests when an abnormality is suspected.
What is the normal Cortisol range?
- Follows a daily rhythm, so timing matters: morning (about 8 am) roughly 5-25 mcg/dL, falling to much lower by late evening.
- A single value means little without the time of day; dynamic tests (suppression or stimulation) are used to diagnose.
- Stress, illness, pregnancy and oestrogen raise it.
Your lab's printed range is what counts.
What does a high Cortisol level mean?
- Cushing's syndrome — exogenous (oral, inhaled or topical steroid) or endogenous (pituitary ACTH-producing adenoma, adrenal tumour, ectopic ACTH).
- Acute stress — illness, surgery, severe pain, psychological stress.
- Pregnancy — increased binding protein elevates total cortisol without true excess.
- Severe depression, anorexia, chronic alcoholism — "pseudo-Cushing's".
What does a low Cortisol level mean?
- Primary adrenal insufficiency (Addison's disease) — autoimmune destruction of adrenal cortex is the most common cause; classically presents with hyperpigmentation, fatigue, hypotension, hyponatraemia, hyperkalaemia.
- Secondary adrenal insufficiency — pituitary failure or long-term steroid use suppressing the adrenal axis.
- Adrenal crisis — acute hypotension and shock; life-threatening, often precipitated by infection or surgery.
Symptoms to look out for
- High cortisol (Cushing's): weight gain around the trunk and face, easy bruising, purple stretch marks, high blood pressure, muscle weakness and mood changes.
- Low cortisol (adrenal insufficiency): fatigue, weight loss, low blood pressure, dizziness on standing and salt craving.
- Both develop gradually and need dynamic testing to confirm.
Many out-of-range results cause no symptoms at all - this is context, not a diagnosis.
When to discuss with a doctor
Symptoms suggesting cortisol excess (central obesity, purple striae, easy bruising, proximal muscle weakness, uncontrolled hypertension or diabetes) warrant endocrinology referral for confirmatory testing (24-hour urinary cortisol, low-dose dexamethasone suppression test, late-night salivary cortisol). Symptoms suggesting deficiency (fatigue, dizziness on standing, hyperpigmentation, salt craving, GI symptoms) need urgent evaluation — adrenal crisis is a medical emergency. Patients on long-term steroids should NEVER stop abruptly. Mediora.AI flags cortisol values in time-of-day context where available.
Related markers
Commonly confused with
- Adrenocorticotropic hormone (ACTH) Cause and effect on the same form. ACTH is the pituitary's instruction; cortisol is what the adrenal glands produce in response. Reading them together is what shows where a problem sits - above or below.