A laboratory test that measures blood cortisol to evaluate adrenal gland function. It is used in the diagnosis of Cushing syndrome and adrenal insufficiency.
Indication
- Suspected Cushing syndrome (weight gain, moon face, purple stretch marks)
- Suspected Addison disease / adrenal insufficiency (fatigue, low blood pressure, skin darkening)
- Investigation of unexplained hypertension and hypokalemia
- Evaluation of hypoglycemic episodes
- Assessment of adrenal reserve after long-term corticosteroid therapy
- Workup of an incidentally found adrenal mass (incidentaloma)
- Suspected ectopic ACTH syndrome
Preparation
- Because of the circadian rhythm, samples are usually drawn between 07:00-09:00 in the morning
- A second sample may sometimes be requested around 23:00 in the evening
- Rest quietly for 30 minutes before sample collection
- Inform the physician about estrogens, corticosteroids, and other relevant medications
- In the ACTH stimulation test, samples are taken at 30 and 60 minutes after a 250 mcg ACTH injection
How it's performed
- A blood sample is taken from a vein in the arm
- Morning and evening samples are used to assess the circadian rhythm
- Salivary cortisol or 24-hour urinary free cortisol may also be measured
- In the ACTH stimulation test, synthetic ACTH is given intravenously
- Blood is drawn at set intervals after stimulation to evaluate the response
- Low-dose or high-dose dexamethasone suppression tests provide additional diagnostic information
Post-procedure
- Results are interpreted together with clinical findings
- If cortisol is elevated, the source is investigated (pituitary or adrenal MRI/CT)
- If cortisol is low, hormone replacement therapy is planned
- Periodic follow-up may be required during long-term care
- Collaboration with the endocrinology department is recommended
Risks
- Mild pain or bruising at the puncture site
- Stress and sleep disturbance can produce misleading results
- Some medications (estrogens, phenytoin) can affect the result
- Rare skin reaction during the ACTH stimulation test
- Values may be transiently elevated under stress
FAQ
Why is cortisol measured in the morning?
Cortisol secretion follows a circadian rhythm, with peak levels between 06:00-08:00 and the lowest values around midnight. The morning sample reflects the daily peak of the adrenal gland.
Does stress affect the result before the test?
Yes. Physical and psychological stress, acute illness, and intense exercise can elevate values. For this reason, resting before sample collection is recommended.
What is the ACTH stimulation test?
After synthetic ACTH is injected intravenously, the cortisol response is measured. It evaluates the adrenal gland's ability to respond to stimulation and is particularly important in diagnosing adrenal insufficiency.
Does a high cortisol always mean Cushing syndrome?
No. Stress, pregnancy, depression, and obesity can also raise the values. Additional tests and clinical evaluation are essential for diagnosis.
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