The preparation
There are a few points to consider in the preparation. The patient should be fasting when taking the blood sample so that the values are not falsified. However, sufficient water (no coffee, no other sweet drinks such as orange juice) should be drunk.
An increased amount of liquid makes it easier to take the blood sample. Furthermore, some foods should not be distorted. However, these should be mentioned in the scheme you receive from your doctor. This scheme explains the individual points of the test in detail and tells you the times at which you should take dexamethasone.
The procedure
If the indication is given, the dexamethasone inhibition test should be prepared. The doctor treating you should explain the reasons for carrying out the test and make them clear. First, the dexamethasone short test is performed.
For this, blood is taken from the patient at 8 a.m. and the amount of cortisol is determined. On the same day, the patient should take the dexamethasone at 11 pm and have another blood sample taken at 8 am the next morning. Depending on the result, the long-term test is then carried out.
The procedure of the long-term test is different or depends on the laboratory that evaluates the test. However, special schemes are available for this purpose, which are handed out to you by the attending physician. After the evaluation of the findings, the further course of the test should be discussed if the test result is positive. In most cases, imaging is performed to rule out tumorous changes.
The evaluation
First of all, one should know that a positive result does not necessarily prove a Cushing’s syndrome. For example, some medications (antiepileptic drugs) can influence the result. A lot of stress or mental illness, such as depression, also have an influence on the cortisol level.
Further tests can be carried out as a supplement to confirm the diagnosis once and for all. When performing the short test, the cortisol level should drop in a healthy person after dexamethasone administration. If this is not the case, it is very likely that a Cushing’s syndrome is present, which should be further clarified by differential diagnosis.
A distinction can be made between primary and secondary Cushing’s syndrome. A primary Cushing’s syndrome is caused by a tumorous change in the adrenal cortex. In this case, further diagnosis should be made by imaging procedures (ultrasound, MRI).
A secondary Cushing’s syndrome is caused by a disorder of the pituitary gland or the hypothalamus. Here, too, tumorous changes, such as an adenoma of the pituitary gland, can be the cause. Further imaging is also recommended in this case.
