Cortisol Suppression Test (Dexamethasone Suppression) (ACTH suppression)
Cortisol Suppression Test
Sample for a cortisol suppression test:
Rapid cortisol suppression test:
- This test is easy and quick to perform.
- This is used as a screening test for Cushing’s syndrome.
- Obtain 4 ml of fasting blood at 8 AM.
- Inject I/M or I/V cortisone.
- Collect blood 5 ml after 30 and 60 minutes of injection.
- Serum or heparinized blood can be used.
Prolonged suppression test:
- Obtain 24 hours of urine as a baseline sample.
- Collect blood for baseline cortisol level.
- Collect 24 hours urine samples daily for 6 days.
- On day 3, give a low dose of dexamethasone by mouth (with antacid or milk).
- On day 5, give a high dose of dexamethasone by mouth like above.
- Keep the urine refrigerated.
Protocol for an overnight low-dose dexamethasone suppression test:
- One mg of dexamethasone is given at night at 11 PM.
- Collect the blood at 8 AM.
- A normal person’s cortisol concentration is suppressed to 2 µg/dL or less.
- Cushing’s patient does not show suppression, and the level may be >10 µg/dL.
Purpose of the test (Indications)
- This test is done to diagnose adrenal hyperfunction (Cushing’s Syndrome).
- This also diagnoses adrenal hypofunction (Addison’s disease).
Pathophysiology of Cortisol
- Corticotropin-releasing hormone (CRH) is made in the hypothalamus.
- CRH stimulates the production of ACTH from the anterior pituitary gland.
- ACTH stimulates the adrenal gland cortex (zona fscicultra) to produce cortisol.
- The feedback mechanism is rising levels of negative cortisol feedback, stopping the further production of CRH and ACTH.
- Cortisol is a potent glucocorticoid released from the adrenal cortex (zona fasciculta)
- Cortisol hormone affects the metabolism of:
- The main effect is on the glucose level.
- Cushing’s syndrome is due to bilateral adrenal hyperplasia.
- The pituitary gland only responds to the high level of cortisol (corticosteroids).
- Cushing’s syndrome due to adrenal adenoma or cancer, cortisol secretion continues despite a decrease in ACTH.
- Cushing’s syndrome due to ectopic ACTH-producing tumors, there is the secretion of ACTH despite high cortisol levels.
Interpretations of cortisol suppression test:
- Suppression occurs in patients with:
- Cushing’s syndrome where the level is >10 µg/dL.
- In 50% of the cases, the cause is endogenous.
- There is no suppression in patients with:
- Adrenal Adenoma.
- Adrenal carcinoma.
- In the case of ectopic ACTH-producing neoplasm.
Table showing the relation of Cushing’s syndrome with the dose of cortisone:
|Disease||Causative reason||low dose||High Dose|
|Cushing’s syndrome||Bilat. adrenal hyperplasia||No change||>50 % reduction in cortisol|
|Cushing’s syndrome||Adrenal adenoma or carcinoma||No change||No change|
|Cushing’s syndrome||Ectopic ACTH tumors||No change||No change|
- Absent or failure response to cortisol stimulation seen in:
- Addison’s disease (adrenal insufficiency).
- Hypopituitarism (secondary adrenal insufficiency).
- Adrenal adenoma and carcinoma.
- Respond to cortisol stimulation indicate adrenal hyperplasia (Cushing’s syndrome).
Adrenal hyperfunction is seen in the following conditions:
- Cushing’s Syndrome.
- Ectopic ACTH- producing tumors
- Adrenal adenoma or carcinoma.
- Bilateral adrenal hyperplasia.
- Mental depression.
Adrenal Hypofunction is seen in:
- Addison’s disease.
- Neoplastic infiltration.
- Granulomatous inflammation like TB, histoplasmosis, and sarcoidosis.
- After adrenalectomy.
Differential diagnosis of adrenal gland tumors:
|Test||Normal||Cushing’s Syndrome||Adrenal tumor||Ectopic ACTH|
|Urinary free cortisol||<100 µg/day||>120 µg/day||>120 µg/day||>120µg/day|
|Serum cortisol||<3 µg/dL||>10 µg/dL||>10 µg/dL||>120 µg/dL|
|H.D Dexamethasone||50% supp.||Most supp.||Fail to supp.||fail to supp|
Supp = suppression.
H.D = high dose.
Questions and answers:
Question 1: What is the significance of cortisol suppression test?
Suppression occurs in Cushing's syndrome.
Question 2: In what cases there is no suppression of cortisol?
There is no suppression in the adrenal adenoma, adrenal carcinoma and ectopic ACTH production.