A short Dexamethasone Suppression Test (DST) is a medical procedure designed to evaluate the body’s hormone regulation system. This test helps healthcare professionals assess the function of specific glands involved in hormone production and is commonly used to investigate conditions related to hormone imbalances. It serves as a diagnostic tool for various health concerns.
What is the Short DST?
The Short Dexamethasone Suppression Test, often referred to as the overnight DST, is a screening test that examines the body’s ability to regulate cortisol, a steroid hormone. Cortisol is produced by the adrenal glands, which are located on top of each kidney. This hormone plays diverse roles, including helping the body respond to stress, regulating metabolism, influencing blood sugar levels, and controlling inflammation.
The test evaluates the hypothalamic-pituitary-adrenal (HPA) axis, a complex communication system involving the hypothalamus in the brain, the pituitary gland, and the adrenal glands. Normally, this axis maintains cortisol levels within a healthy range through a feedback loop. Dexamethasone, a synthetic corticosteroid similar to cortisol, is administered to mimic the body’s natural cortisol and signals the pituitary gland to reduce the release of adrenocorticotropic hormone (ACTH), which lowers cortisol production from the adrenal glands.
Preparing for and Undergoing the Test
Preparing for the Short DST involves instructions for accurate results. Patients may be advised to avoid certain medications, such as estrogens, anticonvulsants, or other steroid-containing drugs, before the test, as these can interfere with cortisol levels or dexamethasone metabolism. Alcohol consumption and significant stress should also be avoided, as they can temporarily affect cortisol regulation.
The procedure is straightforward and typically performed overnight. The patient takes a single 1-milligram dose of dexamethasone orally, usually between 10:00 PM and 11:00 PM. The following morning, between 8:00 AM and 9:00 AM, a blood sample is drawn to measure the body’s cortisol level. This timing is used because cortisol levels naturally peak in the early morning, and the test assesses how well this natural rise is suppressed by the administered dexamethasone.
Understanding Your Short DST Results
Interpreting the results of a Short DST involves evaluating the measured cortisol level after dexamethasone administration. A normal outcome indicates proper function of the HPA axis, where the dexamethasone successfully suppresses cortisol production. This is typically reflected by a morning cortisol level below 1.8 micrograms per deciliter (mcg/dL) or 50 nanomoles per liter (nmol/L).
Conversely, an abnormal result occurs when cortisol levels remain elevated and do not suppress sufficiently after the dexamethasone dose. This lack of suppression suggests that the body may be producing too much cortisol independently of the normal regulatory signals. While an abnormal result can indicate conditions like Cushing’s syndrome, it is important to note that other factors, such as severe stress, obesity, alcohol use, or certain medications, can also lead to false positive results.
What Happens After an Abnormal Result?
An abnormal Short DST result does not confirm a specific diagnosis but indicates a need for further medical evaluation. It suggests that the body’s cortisol regulation may be disrupted, requiring additional testing to identify the underlying cause. Healthcare providers will typically recommend more comprehensive tests to pinpoint the source of the elevated cortisol.
These follow-up investigations may include collecting 24-hour urine samples to measure total cortisol excretion or conducting midnight salivary cortisol tests to reveal abnormal cortisol patterns throughout the day. Measuring ACTH levels in the blood can also help determine if the problem originates in the pituitary gland or the adrenal glands. Patients with abnormal results are often referred to an endocrinologist, a specialist in hormone disorders, to guide further diagnostic steps and determine the appropriate course of action.