Dexamethasone is a man-made or synthetic type of steroid which is similar to cortisol. The dexamethasone suppression test is a way to diagnose Cushing Syndrome. It measures levels of adrenocorticotropic hormone (or ACTH) secretion by your pituitary gland.
What is the Dexamethasone Suppression Test?
The dexamethasone suppression test measures cortisol levels in your blood. After receiving a dose of dexamethasone, cortisol secretion should decrease. Your body is reacting abnormally if it still produces too much ACTH.
There are two types of the dexamethasone suppression test, which are low dose suppression test and the high dose suppression test. These two types of processes can be used to administer this test.
Low dose test
This test is conducted to find out whether or not you have Cushing Syndrome. The low dose test is the first line of screening for Cushing Syndrome. 1 mg of dexamethasone is the typical dose.
The overnight low dose type of dexamethasone suppression test is administered through an oral dose of 1 mg of dexamethasone at 11:00 PM. At 9:00 AM the next day, a blood sample will be taken from you.
It is important to have your blood taken at this time because having your blood taken at any later time can produce a false-positive result. Plasma cortisol is then measured. A normal result should show that your cortisol has been suppressed to < 50 nmol/L. You may also take a low dose test which lasts for 48 hours.
On the first day, a baseline blood sample will be taken from you. On the second day, you will be given your first dose of dexamethasone at 9:00 AM. You will be given a total of 9 0.5 mg tablets of dexamethasone which includes the first tablet, and a spare tablet in case of mishaps. Tablets will then be taken at 3:00 PM, 9:00 PM, 3:00 AM, and 9:00 AM. On the third day, you will return for your second blood test.
High dose test
This is given to those who have Cushing Syndrome to find out if it is caused by a tumor on the pituitary gland. 8 mg of dexamethasone is the typical dose.
Who Needs to take the Dexamethasone Suppression Test?
The dexamethasone suppression test is given to those who may be producing too much cortisol. If you have symptoms of Cushing Syndrome, you may have to take the dexamethasone suppression test. Taking the test can help Cushing Syndrome be diagnosed. Only around 2% of those with Cushing Syndrome will suppress cortisol levels, and only around 2% of those without Cushing Syndrome will fail to suppress cortisol levels.
When your body has been exposed to cortisol for a long time, you may have Cushing Syndrome. It is a disorder that can be caused by an adrenal tumor, a pituitary tumor, or any other tumor which causes your body to produce too much ACTH.
Cushing Syndrome or hypercortisolism can occur if your body produces too much cortisol or if you take corticosteroid medication. There are many symptoms of Cushing Syndrome. The symptoms will appear depending on how much excess cortisol is in your body.
Cushing Syndrome Symptoms
|Acne||Blood pressure changes|
|Bone loss||Slow Healing of Wounds|
|Depression||More visible body and facial hair (women)|
|Easy bruising||Erectile dysfunction|
|Irritability||Pink and purple stretch marks on your abdomen, arms, breasts, and thighs|
|Decrease fertility and libido||Weight gain on the face, between your shoulders, on your midsection, or on your upper back|
Other health conditions can cause you to have high levels of cortisol as well.
These conditions can cause high levels of cortisol:
- Heart attack
- Alcohol dependency
- Anorexia nervosa
- Overactive thyroid gland
- Heart failure
- Poor diet
- Untreated diabetes
The dexamethasone suppression test is generally. However, pregnancy and medication for seizures can affect test results. Taking birth control pills may affect your test results as well.
Dexamethasone Suppression Test and Results: Before, During, and After the Test
Before the Test
There is no need to do anything differently before the test. But if you have diabetes, you should inform your doctor as blood sugar may arise during the test.
If you take any medication, you should inform your doctor or healthcare provider. Certain kinds of medication can affect the results of the dexamethasone suppression test.
You may also be required to stop taking certain kinds of medication before you take the dexamethasone suppression test. For instance, if you take oral contraceptives you may be asked to stop taking your birth control 6 weeks before taking the dexamethasone suppression test. You should only stop taking your medication if you are required to do so by your doctor or healthcare provider.
If you take any of the following medications, then you may have to stop taking them before taking the dexamethasone suppression test:
- Medication that contains corticosteroids such as hydrocortisone and prednisone
- Oral birth control pills
Additionally, false positives may occur for the following situation:
- On a dialysis
- Under medication that inhibits CYP3A4
- Consumed alcohol before taking the test
- Has chronic alcohol abuse or alcohol dependence
- Liver failure
- Nephrotic syndrome
- Renal failure
- Other serious illness
- Uncontrolled diabetes
- Antibiotic intake such as rifampicin
- Under medication for epilepsy and seizures, such as carbamazepine, phenobarbitone, or phenytoin
If you have other health conditions, you should inform your doctor or healthcare provider.