Cortisol
Cortisol· also: AM Cortisol
Clinical Overview
Cortisol is the primary glucocorticoid hormone produced by the adrenal cortex under the influence of ACTH from the pituitary gland. It regulates metabolism, immune response, blood pressure, and the stress response. Cortisol follows a clear circadian rhythm — peak levels are in the morning (7–9 AM) and lowest levels are at midnight.
Why This Test Matters
Cortisol measurement is essential for diagnosing Cushing's syndrome (cortisol excess — from adrenal tumor, pituitary tumor/Cushing's disease, or ectopic ACTH) and Addison's disease (primary adrenal insufficiency). Cortisol levels alone are insufficient for diagnosis — stimulation tests (ACTH stimulation test for adrenal insufficiency) and suppression tests (dexamethasone suppression test for Cushing's) are required for definitive diagnosis.
Reference RangesWHO/IFCC standards
| Age Group | Reference Range | Unit | Notes |
|---|---|---|---|
| Adults (18–64) | 6 – 23 | µg/dL | Morning (8 AM) |
| Adults (18–64) | 2 – 12 | µg/dL | Afternoon (4 PM) |
Also reported in: nmol/L.
Critical (Panic) Values
Critical Low: < 2 µg/dL. Values outside these limits require immediate clinical attention.
What Causes Abnormal Results?
High Cortisol Causes
- Cushing's disease (pituitary ACTH-secreting tumor — most common cause)
- Adrenal adenoma or carcinoma
- Ectopic ACTH secretion (small cell lung cancer)
- Exogenous corticosteroid therapy (most common overall cause of high cortisol effect)
- Physical stress (surgery, illness, trauma)
- Severe depression and anxiety (pseudo-Cushing's)
- Pregnancy
Low Cortisol Causes
- Addison's disease (primary adrenal insufficiency — autoimmune, TB, metastases)
- Secondary adrenal insufficiency (pituitary ACTH deficiency)
- Abrupt withdrawal of long-term corticosteroid therapy
- Waterhouse-Friderichsen syndrome (adrenal hemorrhage in meningococcal sepsis)
Signs & Symptoms to Watch For
How to Prepare for This Test
For morning cortisol: draw at 7–9 AM. For afternoon cortisol: draw at 3–5 PM. Patients must be awake for at least 2 hours. Avoid physical stress before testing. Inform your doctor of any corticosteroid use (including inhaled, topical, and nasal steroids).
Factors That Can Affect Results
- Time of day (mandatory consideration — diurnal variation is large)
- Exogenous corticosteroids (raise cortisol, including inhaled and topical steroids)
- Physical illness and surgery (markedly raise cortisol)
- CBG (cortisol-binding globulin): elevated in pregnancy and oral contraceptive use (raises total cortisol without raising free cortisol)
- Obesity and depression (can cause mild cortisol excess mimicking Cushing's)
Related Topics
Frequently Asked Questions
What tests are used to diagnose Cushing's syndrome?
Three first-line tests can screen for Cushing's syndrome: (1) 24-hour urine free cortisol (UFC) — elevated in Cushing's; (2) late-night salivary cortisol (collected at 11 PM–midnight when cortisol should be lowest) — elevated in Cushing's; (3) overnight 1 mg dexamethasone suppression test (DST) — cortisol should suppress below 1.8 µg/dL in normal individuals but fails to suppress in Cushing's. Two abnormal tests are required to confirm the diagnosis before further localization studies.
What is an adrenal crisis and how is it treated?
Adrenal crisis is a life-threatening emergency caused by acute cortisol deficiency, typically triggered by illness, surgery, or injury in a patient with unrecognized adrenal insufficiency or abrupt steroid withdrawal. Symptoms include severe hypotension, abdominal pain, vomiting, confusion, and shock. Treatment is immediate IV hydrocortisone 100 mg bolus, followed by continuous infusion, plus IV saline. Every patient with known adrenal insufficiency should carry an emergency hydrocortisone injection kit.