Cortisol Suppression Test (Dexamethasone Suppression) (ACTH suppression)
Sample
- Rapid cortisol suppression test:
- This test is easy and quick to perform.
- This is used as a screening for Cushing’s syndrome.
- Obtain 4 ml of fasting blood at 8 AM.
- Inject I/M or /V cortisone.
- Collect blood 5 ml after 30 and 60 min. 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 sample 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 given at night at 11 PM.
- Collect the blood in the morning at 8 AM.
- In a normal person, 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
- Corticotropin-releasing hormone (CRH) 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 cortisol negative feedback, stop further production of CRH and ACTH.
- Cortisol is a potent glucocorticoid released from the adrenal cortex (zona fasciculta)
- Cortisol hormone affects the metabolism of:
- Carbohydrates.
- Proteins.
- Fats.
- The main effect on the glucose level.
- Cushing’s syndrome 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.
Normal interpretations
- 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:
- 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.
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.