|Dexamethasone suppression test|
|Purpose||assess adrenal gland function|
The dexamethasone suppression test (DST) is used to assess adrenal gland function by measuring how cortisol levels change in response to oral doses or an injection of dexamethasone.  It is typically used to diagnose Cushing's syndrome.
The DST was historically used for diagnosing depression, but by 1988 it was considered to be "at best, severely limited in its clinical ability" for this purpose. 
Dexamethasone is an exogenous steroid that provides negative feedback to the pituitary gland to suppress the secretion of adrenocorticotropic hormone (ACTH). Specifically, dexamethasone binds to glucocorticoid receptors in the anterior pituitary gland, which lie outside the blood-brain barrier, resulting in regulatory modulation. 
There are several types of DST procedures: 
Low-dose and high-dose variations of the test exist.  The test is given at low (usually 1–2 mg) and high (8 mg) doses of dexamethasone, and the levels of cortisol are measured to obtain the results. 
A low dose of dexamethasone suppresses cortisol in individuals with no pathology in endogenous cortisol production. A high dose of dexamethasone exerts negative feedback on pituitary neoplastic ACTH-producing cells (Cushing's disease), but not on ectopic ACTH-producing cells or adrenal adenoma (Cushing's syndrome).[ citation needed ]
A normal result is a decrease in cortisol levels upon administration of low-dose dexamethasone. Results indicative of Cushing's disease involve no change in cortisol on low-dose dexamethasone, but inhibition of cortisol on high-dose dexamethasone. If the cortisol levels are unchanged by low- and high-dose dexamethasone, then other causes of Cushing's syndrome must be considered with further work-up necessary. After the high-dose dexamethasone, it may be possible to make further interpretations. 
|is suppressed by low or high doses||Undetectable or low||Primary hypercortisolism is likely; Cushing's syndrome, not disease (i.e., the hypercortisolism is not driven by ACTH hypersecretion)|
|is not suppressed by low doses, but is suppressed by high doses||Normal to elevated but not in hundreds||Cushing's disease should be considered because the pituitary still retains some feedback control. A pituitary MRI would be needed to confirm.|
|is not suppressed by high or low doses||Elevated in hundreds||Ectopic ACTH syndrome is likely. If an adrenal tumor is not apparent, a chest CT and abdominal CT is indicated to rule out a different tumor secreting ACTH.|
†ACTH as measured prior to dosing of dexamethasone 
Equivocal results should be followed by a corticotropin-releasing hormone stimulation test, with inferior petrosal sinus sampling.
The adrenal glands are endocrine glands that produce a variety of hormones including adrenaline and the steroids aldosterone and cortisol. They are found above the kidneys. Each gland has an outer cortex which produces steroid hormones and an inner medulla. The adrenal cortex itself is divided into three main zones: the zona glomerulosa, the zona fasciculata and the zona reticularis.
Adrenocorticotropic hormone is a polypeptide tropic hormone produced by and secreted by the anterior pituitary gland. It is also used as a medication and diagnostic agent. ACTH is an important component of the hypothalamic-pituitary-adrenal axis and is often produced in response to biological stress. Its principal effects are increased production and release of cortisol by the cortex of the adrenal gland. ACTH is also related to the circadian rhythm in many organisms.
Cushing's syndrome is a collection of signs and symptoms due to prolonged exposure to glucocorticoids such as cortisol. Signs and symptoms may include high blood pressure, abdominal obesity but with thin arms and legs, reddish stretch marks, a round red face, a fat lump between the shoulders, weak muscles, weak bones, acne, and fragile skin that heals poorly. Women may have more hair and irregular menstruation. Occasionally there may be changes in mood, headaches, and a chronic feeling of tiredness.
The hypothalamic–pituitary–adrenal axis is a complex set of direct influences and feedback interactions among three components: the hypothalamus, the pituitary gland, and the adrenal glands.
A major organ of the endocrine system, the anterior pituitary is the glandular, anterior lobe that together with the posterior lobe makes up the pituitary gland (hypophysis). The anterior pituitary regulates several physiological processes, including stress, growth, reproduction, and lactation. Proper functioning of the anterior pituitary and of the organs it regulates can often be ascertained via blood tests that measure hormone levels.
Cortisol is a steroid hormone, in the glucocorticoid class of hormones. When used as a medication, it is known as hydrocortisone.
Addison's disease, also known as primary adrenal insufficiency, is a rare long-term endocrine disorder characterized by inadequate production of the steroid hormones cortisol and aldosterone by the two outer layers of the cells of the adrenal glands, causing adrenal insufficiency. Symptoms generally come on slowly and insidiously and may include abdominal pain and gastrointestinal abnormalities, weakness, and weight loss. Darkening of the skin in certain areas may also occur. Under certain circumstances, an adrenal crisis may occur with low blood pressure, vomiting, lower back pain, and loss of consciousness. Mood changes may also occur. Rapid onset of symptoms indicates acute adrenal failure which is a serious and emergent condition. An adrenal crisis can be triggered by stress, such as from an injury, surgery, or infection.
Cushing's disease is one cause of Cushing's syndrome characterised by increased secretion of adrenocorticotropic hormone (ACTH) from the anterior pituitary. This is most often as a result of a pituitary adenoma or due to excess production of hypothalamus CRH that stimulates the synthesis of cortisol by the adrenal glands. Pituitary adenomas are responsible for 80% of endogenous Cushing's syndrome, when excluding Cushing's syndrome from exogenously administered corticosteroids. The equine version of this disease is Pituitary pars intermedia dysfunction.
Adrenal insufficiency is a condition in which the adrenal glands do not produce adequate amounts of steroid hormones, primarily cortisol; but may also include impaired production of aldosterone, which regulates sodium conservation, potassium secretion, and water retention. Craving for salt or salty foods due to the urinary losses of sodium is common.
Corticotropes are basophilic cells in the anterior pituitary that produce pro-opiomelanocortin (POMC) which undergoes cleavage to adrenocorticotropin (ACTH), β-lipotropin (β-LPH), and melanocyte-stimulating hormone (MSH). These cells are stimulated by corticotropin releasing hormone (CRH) and make up 15–20% of the cells in the anterior pituitary. The release of ACTH from the corticotropic cells is controlled by CRH, which is formed in the cell bodies of parvocellular neurosecretory cells within the paraventricular nucleus of the hypothalamus and passes to the corticotropes in the anterior pituitary via the hypophyseal portal system. Adrenocorticotropin hormone stimulates the adrenal cortex to release glucocorticoids and plays an important role in the stress response.
Hypopituitarism is the decreased (hypo) secretion of one or more of the eight hormones normally produced by the pituitary gland at the base of the brain. If there is decreased secretion of one specific pituitary hormone, the condition is known as selective hypopituitarism. If there is decreased secretion of most or all pituitary hormones, the term panhypopituitarism is used.
Metyrapone, sold under the brand name Metopirone, is a medication which is used in the diagnosis of adrenal insufficiency and occasionally in the treatment of Cushing's syndrome (hypercortisolism).
In humans and other animals, the adrenocortical hormones are hormones produced by the adrenal cortex, the outer region of the adrenal gland. These polycyclic steroid hormones have a variety of roles that are crucial for the body’s response to stress, and they also regulate other functions in the body. Threats to homeostasis, such as injury, chemical imbalances, infection, or psychological stress, can initiate a stress response. Examples of adrenocortical hormones that are involved in the stress response are aldosterone and cortisol. These hormones also function in regulating the conservation of water by the kidneys and glucose metabolism, respectively.
Pseudo-Cushing's syndrome is a medical condition in which patients display the signs, symptoms, and abnormal hormone levels seen in Cushing's syndrome. However, pseudo-Cushing's syndrome is not caused by a problem with the hypothalamic-pituitary-adrenal axis as Cushing's is; it is mainly an idiopathic condition, however a cushingoid appearance is sometimes linked to excessive alcohol consumption. Elevated levels of total cortisol can also be due to estrogen found in oral contraceptive pills that contain a mixture of estrogen and progesterone. Estrogen can cause an increase of cortisol-binding globulin and thereby cause the total cortisol level to be elevated.
The ACTH test is a medical test usually requested and interpreted by endocrinologists to assess the functioning of the adrenal glands' stress response by measuring the adrenal response to adrenocorticotropic hormone or another corticotropic agent such as tetracosactide or alsactide (Synchrodyn). ACTH is a hormone produced in the anterior pituitary gland that stimulates the adrenal glands to release cortisol, dehydroepiandrosterone (DHEA), dehydroepiandrosterone sulfate (DHEA-S), and aldosterone.
Corticorelin is a diagnostic agent. It is a synthetic form of human corticotropin-releasing hormone (hCRH).
Critical illness–related corticosteroid insufficiency is a form of adrenal insufficiency in critically ill patients who have blood corticosteroid levels which are inadequate for the severe stress response they experience. Combined with decreased glucocorticoid receptor sensitivity and tissue response to corticosteroids, this adrenal insufficiency constitutes a negative prognostic factor for intensive care patients.
Hypoadrenocorticism in dogs, or, as it is known in people, Addison's disease, is an endocrine system disorder that occurs when the adrenal glands fail to produce enough hormones for normal function. The adrenal glands secrete glucocorticoids such as cortisol and mineralocorticoids such as aldosterone; when proper amounts of these are not produced, the metabolic and electrolyte balance is upset. Mineralocorticoids control the amount of potassium, sodium, and water in the body. Hypoadrenocorticism is fatal if left untreated.
Pituitary pars intermedia dysfunction (PPID), or equine Cushing's disease, is an endocrine disease affecting the pituitary gland of horses. It is most commonly seen in older animals, and is classically associated with the formation of a long, wavy coat (hirsutism) and chronic laminitis.
Primary pigmented nodular adrenocortical disease (PPNAD) was first coined in 1984 by Carney et al. it often occurs in association with Carney complex (CNC). CNC is a rare syndrome that involves the formation of abnormal tumours that cause endocrine hyperactivity.