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. The dexamethasone suppression test measures levels of adrenocorticotropic hormone (or ACTH) secretion by your pituitary gland. During the dexamethasone suppression test, your blood is drawn and the cortisol level in your blood is then measured.
What is the Dexamethasone Suppression Test?
The dexamethasone suppression test measures cortisol levels in your blood. When you take a dose of dexamethasone, your body should produce less cortisol. Normally, people produce less ACTH after taking the test. Taking the dexamethasone suppression test should reduce or ‘suppress’ your body’s cortisol level. If you produce too much ACTH after taking a dose of dexamethasone, then your body is reacting abnormally, as cortisol secretion should decrease after receiving a dose of dexamethasone.
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.
The low dose test is administered 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 high dose test is given to those who are known to have Cushing Syndrome. The high dose test is administered to find out if the Cushing Syndrome is caused by a tumor on your pituitary gland. 8 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.
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 a disorder which can be caused by an adrenal tumor, a pituary 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.
The following are symptoms of Cushing Syndrome:
- blood pressure changes or worsens
- bone loss
- cognitive difficulties
- fragile skin that easily bruises
- having bites, cuts, and infections that take a long time to heal
- irritability or loss of emotional control
- men may have decreased fertility and libido, and erectile dysfunction
- muscle weakness
- pink and purple stretch marks on your abdomen, arms, breasts, and thighs
- severe fatigue
- weight gain on the face, between your shoulders, on your midsection, or on your upper back
- women may have thick or more visible body and facial hair and irregular or absent periods
Other health conditions can cause you to have high levels of cortisol as well.
These conditions can cause high levels of cortisol:
- a heart attack
- alcohol dependency
- anorexia nervosa
- having an overactive thyroid gland
- heart failure
- poor diet
- untreated diabetes
The dexamethasone suppression test is generally safe for everyone. There are no side effects of taking the test. However, the dexamethasone suppression test is not ideal for everybody. Pregnancy and medication for seizures can affect test results. Taking birth control pills may affect your test results as well. If the dexamethasone suppression test is not for you, then you may be given other tests for Cushing Syndrome.
Dexamethasone Suppression Test and Results: Before, During, and After the Test
Before the Test
Generally, there is no need to do anything differently before taking the dexamethasone suppression test. You can eat and drink normally. However, you should inform your doctor or healthcare provider if you have diabetes. Blood sugar may rise during the test. Your doctor or healthcare provider may either increase your required dose of insulin or test your blood glucose more frequently 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 if:
- you are on dialysis
- you are on medication that inhibits CYP3A4
- you consume alcohol before taking the test
- you have chronic alcohol abuse or alcohol dependence
- you have depression
- you have liver failure
- you have nephrotic syndrome
- you have renal failure
- you have some other serious illness
- you have uncontrolled diabetes
- you take antibiotics, such as rifampicin
- you take diuretics
- you take 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.
The Dexamethasone Suppression Test Process