Cortisol
Cortisol is the primary glucocorticoid hormone made by the adrenal cortex. It follows a strong diurnal rhythm — highest in the early morning (6–8 AM), lowest at midnight. Cortisol regulates blood sugar, blood pressure, immune response, and the body's stress response. Clinical testing includes morning cortisol, midnight cortisol, 24-hour urinary cortisol, and dynamic tests (dexamethasone suppression for Cushing's, ACTH stimulation for Addison's).
Reference Ranges
Male
6 – 23
µg/dL
Female
6 – 23
µg/dL
Child
Consult pediatrician
Reference ranges may vary by laboratory. Always compare with the range printed on your lab report.
What Low Levels Mean
Morning cortisol below 3 µg/dL strongly suggests adrenal insufficiency (Addison's disease, secondary from pituitary failure, or tertiary from chronic steroid use). Symptoms — fatigue, weight loss, hyperpigmentation (Addison's), salt craving, low blood pressure — should prompt ACTH stimulation testing, which is the gold standard diagnostic test. Abrupt stopping of long-term corticosteroids can cause acute adrenal insufficiency — a medical emergency.
What High Levels Mean
Elevated cortisol with lost diurnal rhythm suggests Cushing's syndrome — exogenous steroid use (most common), pituitary adenoma (Cushing's disease), ectopic ACTH production, or adrenal tumor. Symptoms include central obesity with thin limbs, purple abdominal striae, moon face, buffalo hump, hypertension, hyperglycemia, osteoporosis, and mood changes. Screening tests: overnight dexamethasone suppression, late-night salivary cortisol, 24-hour urine free cortisol.
Frequently Asked Questions
Why is cortisol tested in the morning?
Because cortisol follows a strong diurnal rhythm — levels peak around 6–8 AM and decline through the day to a nadir at midnight. Morning cortisol is the most standardized and sensitive time to detect adrenal insufficiency. For Cushing's workup, the loss of this rhythm (high midnight cortisol) is more specific than a high morning value. Timing matters as much as the absolute number.
What is the dexamethasone suppression test?
A screening test for Cushing's syndrome. You take 1 mg of dexamethasone at 11 PM, and cortisol is measured at 8 AM the next morning. In healthy people, dexamethasone suppresses cortisol to below 1.8 µg/dL. Failure to suppress suggests Cushing's. False positives occur with depression, alcohol, severe illness, obesity, and some medications (oral contraceptives). Abnormal results are followed by more specific confirmatory tests.
Can cortisol be tested by saliva?
Yes — late-night salivary cortisol is a sensitive screen for Cushing's syndrome and is increasingly used because it is non-invasive and reflects free (active) cortisol. A single elevated late-night salivary cortisol has high sensitivity for Cushing's. It is particularly useful in patients with variable schedules or those for whom blood draws are difficult. Availability in India is growing but still limited to tertiary centers.
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nmol/LThis information is for educational purposes only and should not replace professional medical advice. Always consult your doctor for interpretation of your test results.
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