Cortisol Axis Test – Types, Procedure and Results
The cortisol axis test is a diagnostic procedure used to evaluate the function of the hypothalamic-pituitary-adrenal axis and assess cortisol production in the body.
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The cortisol axis test is a diagnostic procedure used to evaluate the function of the hypothalamic-pituitary-adrenal axis and assess cortisol production in the body.
What Is the Cortisol Axis Test?
The cortisol axis test is a medical diagnostic procedure used to assess the function of the hypothalamic-pituitary-adrenal (HPA) axis. This axis regulates the production and release of cortisol, a vital stress hormone that controls numerous body functions. The test helps determine whether the HPA axis is overactive or underactive and whether a disorder in cortisol production is present.
The HPA Axis and Cortisol
The HPA axis is a complex feedback system consisting of three key structures:
- Hypothalamus: Releases corticotropin-releasing hormone (CRH).
- Pituitary gland: Responds to CRH by secreting adrenocorticotropic hormone (ACTH).
- Adrenal cortex: Produces cortisol in response to ACTH stimulation.
Cortisol influences metabolism, immune function, blood pressure, and the stress response. A disruption in this axis can have serious health consequences.
When Is the Cortisol Axis Test Performed?
The test is used when a dysfunction of the HPA axis is suspected. Common indications include:
- Suspected Addison disease (primary adrenal insufficiency)
- Suspected Cushing syndrome (cortisol excess)
- Pituitary insufficiency or tumors
- Unexplained fatigue, weight loss, or low blood pressure
- Monitoring after long-term corticosteroid therapy
- Suspected secondary or tertiary adrenal insufficiency
Test Procedures and Types
Several different test methods are available, selected based on the clinical question:
ACTH Stimulation Test (Synacthen Test)
In the ACTH stimulation test, synthetic ACTH (tetracosactide/Synacthen) is administered intravenously or intramuscularly. Blood samples are then taken at defined time points (usually 30 and 60 minutes) and cortisol levels are measured. A sufficient rise in cortisol indicates an intact adrenal cortex function.
Insulin Tolerance Test (ITT)
The insulin tolerance test is considered the gold standard for assessing the entire HPA axis. Insulin is administered to induce a controlled drop in blood sugar, which acts as a strong physiological stress stimulus, triggering the release of CRH, ACTH, and cortisol. Due to its risks (hypoglycemia), this test is only performed under close medical supervision.
CRH Stimulation Test
In the CRH test, synthetic CRH is injected and the ACTH and cortisol response of the pituitary gland is measured. This test helps distinguish between a pituitary disorder and a hypothalamic disorder.
Dexamethasone Suppression Test
The dexamethasone suppression test is used when Cushing syndrome is suspected. After taking the synthetic corticosteroid dexamethasone, suppression of the body's own cortisol production is assessed. A failure to suppress cortisol suggests pathological cortisol overproduction.
Interpreting the Results
Test results are always interpreted within the clinical context:
- Insufficient cortisol response after stimulation: Suggests adrenal insufficiency (primary, secondary, or tertiary)
- Lack of suppression after dexamethasone: Suggests Cushing syndrome
- Normal cortisol response: Indicates an intact HPA axis
Laboratory values are always assessed together with symptoms and further diagnostic findings. A single measurement is generally not sufficient for a definitive diagnosis.
Risks and Side Effects
Most cortisol axis tests are well tolerated. The insulin tolerance test may cause symptoms of hypoglycemia (sweating, trembling, rapid heartbeat), which is why it is performed exclusively under strict medical supervision. The ACTH stimulation test and the dexamethasone suppression test are considered safe and can be performed on an outpatient basis.
References
- Arlt W. et al. - Adrenal insufficiency. Lancet 2003; 361(9372): 1881-1893.
- Nieman LK. et al. - The diagnosis of Cushing's syndrome: an Endocrine Society Clinical Practice Guideline. Journal of Clinical Endocrinology and Metabolism 2008; 93(5): 1526-1540.
- Bornstein SR. et al. - Diagnosis and Treatment of Primary Adrenal Insufficiency: An Endocrine Society Clinical Practice Guideline. Journal of Clinical Endocrinology and Metabolism 2016; 101(2): 364-389.
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