Cortisol
Cortisol is the body's primary stress hormone. Both excess and deficiency cause distinct, recognisable clinical syndromes — interpretation is time-of-day dependent.
What it measures
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 a high value can 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 a low value can 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.
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.