Over-production of cortisol by the adrenal glands can result in hypertension, along with many other signs and symptoms, including changes in the distribution of fat and hair, and changes in your skin. Collectively, these changes are called Cushing’s syndrome and can be caused by anything that makes the adrenal glands produce more cortisol. To diagnose Cushing’s syndrome, the first step is to measure cortisol levels. There are a variety of approaches to this diagnosis, but two of the most frequently used tests are the measurement of cortisol levels in urine collected over 24-hours, and the dexamethasone suppression test. Since excess cortisol is excreted in the urine, elevated levels over a 24-hour period give an indication that Cushing’s syndrome may be the cause of the hypertension.

A more specific test is the dexamethasone suppression test. In a normal situation, dexamethasone suppresses cortisol production by the adrenal glands. To do the test, the patient is given a dose of dexamethasone at bedtime. In the morning, blood is drawn to determine the plasma cortisol level. In the absence of Cushing’s syndrome, the plasma cortisol will be suppressed to below a certain level. If Cushing’s syndrome is present, no such suppression will be seen. This test can be administered in a variety of ways that help determine why the adrenal glands are producing too much cortisol.