Dexamethasone Suppression Test For Cortisol
Dexamethasone Suppression Test For Cortisol
The dexamethasone suppression test evaluates the ability of the adrenal gland to suppress cortisol secretion. This test can also aid in determining the cause of elevated cortisol levels in the body, such as an overproduction of adrenocorticotrophic hormone (ACTH) by the pituitary gland. The pituitary gland usually regulates the secretion of ACTH based on the amount of cortisol present in the blood plasma. ACTH induces the adrenal cortex to secrete cortisol. When cortisol levels in the plasma go up, the release of ACTH is repressed. Conversely, when cortisol levels decrease, ACTH secretion increases.
Dexamethasone is a synthetic steroid similar to cortisol that effectively inhibits the secretion of ACTH in normal individuals. The administration of dexamethasone will reduce ACTH levels, resulting in a subsequent decrease in cortisol levels. Individuals with overactive pituitary glands that produce excessive amounts of ACTH will exhibit an abnormal response during the low-dose test, while their response to the high dose will be normal. Thus, getting this test done is recommended to evaluate cortisol production.
Symptoms of Cushing's syndrome (excess production of cortisol)
Weight gain
Thin arms and legs
Round face
Increased fat around the base of the neck
Easy bruising
Muscle weakness
Acne
What is the Dexamethasone Suppression Test For used for?
This test is performed to determine
How well the adrenal glands respond to adrenocorticotropic hormone (ACTH)
The effect of the corticosteroid medicine dexamethasone on the cortisol levels in the blood
Preparation for the test
Please tell your healthcare provider if you are taking any medications before undergoing the test, as certain medications may interfere with the accuracy of the test results.
There are two different types of tests: low dose and high dose. Both types can be performed using either an overnight (common) or standard (3-day) method (rare).
Common:
Low-dose overnight: At 11 p.m., you will receive a low-dose overnight of 1 milligram (mg) of dexamethasone. The following morning at 8 a.m., a healthcare professional will collect a blood sample from you to measure your cortisol levels.
High-dose overnight: The healthcare provider will evaluate your cortisol levels on the morning of the test. At 11 p.m., you will be administered 8 mg of dexamethasone. The next morning, at 8 a.m., your blood will be drawn to measure cortisol levels.
Rare:
Standard low-dose: To measure cortisol levels, urine is collected over a span of 3 days using 24-hour collection containers. On the second day, a low dose of dexamethasone (0.5 mg) is taken orally every 6 hours for 48 hours.
Standard high-dose: Cortisol levels will be measured by collecting urine over a 3-day period using 24-hour collection containers. A high dose of dexamethasone (2 mg) will be given orally every 6 hours for 48 hours starting on the second day.
Interpretation of the results
The cortisol level is expected to decrease following the administration of dexamethasone. Normal results are as follows:
Low dose:
Overnight: The plasma cortisol level is less than 1.8 micrograms per deciliter (mcg/dL) or 50 nanomoles per liter (nmol/L) at 8 a.m.
Standard: The urinary-free cortisol level on the third day is less than 10 micrograms per day (mcg/day) or 280 nmol/L.
High dose:
Overnight: More than a 50% decrease in plasma cortisol levels.
Standard: More than a 90% decrease in urinary-free cortisol levels.
Deviation from normal results indicates the following:
a) Abnormal low-dose test results could indicate an abnormal cortisol release (Cushing syndrome). This may be caused by an adrenal tumour that produces cortisol, a pituitary tumour that produces ACTH, or a tumour in the body that produces ACTH (ectopic Cushing syndrome).
b) The high-dose test can help in distinguishing a pituitary cause (Cushing disease) from alternative causes.
· Adrenal gland tumour causing Cushing's syndrome.
Low dose: no change
High dose: no change
· Ectopic ACTH-producing tumour causing Cushing's syndrome.
Low dose: no change
High dose: no change
· Pituitary tumour causing Cushing's syndrome.
Low dose: no change
High dose: normal suppression
FAQs
How is the sample collected for the dexamethasone suppression test for cortisol?
For the common method, a blood sample is collected from a vein in your arm using a small needle. Generally, this process is completed within five minutes. You will also be given sterile containers by your healthcare provider to collect urine samples (rare method). To begin this test, ensure that you empty your bladder in the morning without retaining any urine. It is important to make a note of the time when you do so. Subsequently, collect your urine each time you use the bathroom. Repeat this process for three consecutive days, using three separate 24-hour containers to store the collected urine. Conclude the collection three days later, at the same time you started the process.
Are there any risks associated with the dexamethasone suppression test for cortisol?
The blood test carries risks, such as experiencing a slight sting or bruise, multiple needle punctures, feeling lightheaded, hematoma (blood accumulation under the skin), and infection. Urine sample collection does not pose any risks.
What factors can lead to false test results?
False test results may arise from various factors, such as the use of certain medications, obesity, depression, and stress. False results tend to be more prevalent among women compared to men.
What are the medicines that are believed to interfere with the dexamethasone suppression test for cortisol?
A few medicines that could interfere with the dexamethasone suppression test for cortisol include antibiotics, anti-seizure medicines, corticosteroids, estrogen, contraceptives, and diuretics.
What are the possible treatment options for managing Cushing's syndrome?
The treatment of Cushing's syndrome is determined by the underlying cause and includes a range of options including surgical removal of tumors, radiation therapy, medication to regulate cortisol production and lifestyle modifications.
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