Cortisol
HormonesWhat is Cortisol?
Cortisol is a steroid hormone produced by the adrenal glands, which sit atop each kidney. Often called the "stress hormone," cortisol plays a far broader role than its nickname suggests. It is essential for regulating metabolism, blood sugar levels, blood pressure, immune function, and the body's inflammatory response. Cortisol helps the body mobilize energy during times of physical or psychological stress by increasing glucose availability, enhancing the brain's use of glucose, and suppressing non-essential functions like digestion and reproduction during acute stress responses.
Cortisol follows a strong diurnal (circadian) rhythm, with levels peaking in the early morning around 6–8 AM to help you wake up and gradually declining throughout the day, reaching their lowest point around midnight. This pattern is critical for maintaining normal sleep-wake cycles, energy regulation, and metabolic homeostasis. Cortisol levels are measured through blood, saliva, or 24-hour urine tests, each providing different clinical information. Blood cortisol primarily measures total cortisol (bound and free), while salivary cortisol reflects the biologically active free fraction.
Why It Matters
Cortisol is indispensable for life—without adequate cortisol, the body cannot mount an appropriate stress response, maintain blood pressure, or regulate blood sugar. Chronically elevated cortisol, as seen in Cushing's syndrome, leads to weight gain (especially central obesity), muscle wasting, osteoporosis, high blood pressure, diabetes, immune suppression, and psychiatric disturbances. Cortisol deficiency, as seen in Addison's disease or adrenal insufficiency, can cause life-threatening adrenal crisis with dangerously low blood pressure, severe fatigue, and electrolyte imbalances. Proper cortisol testing is essential for diagnosing these serious endocrine conditions.
Normal Reference Ranges
| Group | Range | Unit |
|---|---|---|
| Morning (6–8 AM) | 6–23 | µg/dL |
| Afternoon (4 PM) | 3–15 | µg/dL |
| 24-hour Urine Free Cortisol | 10–100 | µg/24hr |
Reference ranges may vary by laboratory. Always compare results to the ranges provided by your testing facility.
What High Cortisol Levels Mean
Common Causes
- Cushing's syndrome (pituitary adenoma, adrenal tumor, or ectopic ACTH production)
- Chronic psychological or physical stress
- Exogenous corticosteroid use (prednisone, dexamethasone)
- Major depressive disorder
- Alcoholism (pseudo-Cushing's)
- Obesity
- Pregnancy (physiologically elevated)
Possible Symptoms
- Central obesity with fat accumulation in the face (moon face) and upper back (buffalo hump)
- Thin skin with easy bruising and purple striae on the abdomen
- Muscle weakness and wasting, especially in the limbs
- High blood pressure
- High blood sugar or diabetes
- Osteoporosis and increased fracture risk
- Mood changes including depression, anxiety, and irritability
- Frequent infections due to immune suppression
What to do: Persistently elevated cortisol requires confirmation with multiple tests—typically two or more of: late-night salivary cortisol, 24-hour urinary free cortisol, and overnight dexamethasone suppression test. If Cushing's syndrome is confirmed, imaging (pituitary MRI, adrenal CT) and ACTH levels help determine the source. Treatment depends on the cause: pituitary adenomas are typically treated with transsphenoidal surgery, adrenal tumors with adrenalectomy, and ectopic ACTH sources with removal of the causative tumor. If exogenous steroids are the cause, gradual tapering under medical supervision is essential.
What Low Cortisol Levels Mean
Common Causes
- Primary adrenal insufficiency (Addison's disease, most commonly autoimmune)
- Secondary adrenal insufficiency (pituitary disease reducing ACTH)
- Abrupt withdrawal of chronic corticosteroid therapy
- Pituitary surgery or radiation
- Congenital adrenal hyperplasia
- Adrenal hemorrhage or infarction (Waterhouse-Friderichsen syndrome)
Possible Symptoms
- Severe fatigue and weakness
- Unintentional weight loss and decreased appetite
- Low blood pressure (orthostatic hypotension)
- Hyperpigmentation of skin (in primary adrenal insufficiency)
- Salt cravings
- Nausea, vomiting, and abdominal pain
- Dizziness or fainting
- Low blood sugar (hypoglycemia)
What to do: Low cortisol should be further evaluated with an ACTH stimulation test (cosyntropin test), which is the gold standard for diagnosing adrenal insufficiency. ACTH levels help distinguish primary (high ACTH) from secondary (low ACTH) adrenal insufficiency. Treatment involves lifelong glucocorticoid replacement, typically hydrocortisone 15–25 mg daily in divided doses. Patients must be educated about stress dosing—doubling or tripling their dose during illness, surgery, or significant stress to prevent adrenal crisis. A medical alert bracelet and emergency injectable hydrocortisone are recommended.
When Is Cortisol Testing Recommended?
- When symptoms of Cushing's syndrome are present (central obesity, striae, easy bruising, high blood pressure)
- When adrenal insufficiency is suspected (fatigue, weight loss, low blood pressure, hyperpigmentation)
- Before or after discontinuing long-term corticosteroid therapy
- When evaluating unexplained hypokalemia, hyperglycemia, or osteoporosis
Frequently Asked Questions
Related Biomarkers
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Upload Lab Results →Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Reference ranges may vary between laboratories. Always consult your healthcare provider for interpretation of your specific test results.