Adrenal Function Test – Adrenal Tests
The adrenal gland makes many different hormones and is divided into two distinct zones: the medulla and the cortex. The medulla makes hormones called catecholamines, such as adrenaline. The cortex primarily makes the hormones cortisol and aldosterone. Diseases of the adrenal gland can often be diagnosed with blood tests that measure the levels of these different hormones, although most adrenal gland disorders affect only the adrenal cortex.
Blood cortisol is one of the basic tests used to assess adrenal gland function. Cortisol levels rise and fall throughout the day, so a single blood sample may not be effective at diagnosing a deficiency or overproduction. As a result, multiple samples may be taken. Cortisol levels can also be measured before or after stimulation of the adrenal gland to get a better sense of adrenal function.
Adrenocorticotropin Hormone (ACTH)
Adrenocorticotropin hormone, or ACTH, is a hormone made by the pituitary gland that stimulates the adrenal glands to make cortisol. As a result, it can be measured to assess adrenal function. If the adrenal glands are not working effectively, the pituitary secretes more ACTH to stimulate them to make more cortisol. As a result, people with poorly functioning adrenal glands typically have elevated ACTH levels.
Adrenal Stimulation Test
Another way to more accurately measure adrenal gland function is to measure cortisol levels before and after stimulation of the adrenal glands. For this test, the cortisol level is measured and then the patient is injected with a synthetic form of ACTH called cosyntropin. After 45 minutes, the blood cortisol level is measured again to see if the adrenal glands produce more cortisol in response to the cosyntropin. Failure of the blood cortisol levels to rise suggests adrenal gland malfunction.
The corticotropin-releasing hormone test can also be used to test adrenal gland function. First, baseline levels of ACTH and cortisol are measured. Then, corticotropin-releasing hormone — a chemical that stimulates the release of ACTH — is injected. Cortisol and ACTH levels are measured every 15 minutes. Typically, ACTH levels peak after 15 to 30 minutes, and cortisol levels peak 30 to 40 minutes after the injection of corticotropin-releasing hormone. Failure of cortisol levels to rise after an increase in ACTH suggests adrenal failure.
Adrenal Hormone Tests
The body has two adrenal glands, one located above each kidney. Hormones secreted by these endocrine glands help to regulate many body processes. Measuring blood and urine levels of adrenal hormones, including the following, is often the first step in diagnosing a variety of disorders associated with adrenal gland dysfunction.
Aldosterone controls salt, potassium, and water balance in the body and helps to regulate blood pressure. Overproduction (hyperaldosteronism) or underproduction (hypoaldosteronism) of this hormone may be caused by tumours or other abnormalities within the adrenal glands (primary; e.g., adrenal cancer) or may result from problems outside the adrenals (secondary). Both blood levels and urinary excretion of aldosterone may be measured.
Cortisol is a glucocorticoid hormone that helps to control the metabolism of carbohydrates, proteins, and fats; mediate the body’s response to stress, and regulate the immune system. Oversecretion of cortisol, most often caused by a benign adrenal tumour, results in Cushing’s syndrome. Undersecretion may indicate a form of adrenal insufficiency known as Addison’s disease. Both blood levels and urine levels (known as free cortisol) are usually measured.
18-Hydroxycortisol, a product of cortisol metabolism, is an unusual steroid produced in excessive amounts in patients with primary hyperaldosteronism. Measuring blood levels of this hormone can help to determine whether primary hyperaldosteronism is caused by a tumour called adrenal adenoma, or by overgrowth (hyperplasia) of adrenal tissue; levels are significantly higher in people with an adenoma.
DHEA-S, or dehydroepiandrosterone-sulfate—a sex hormone (androgen) synthesized by the adrenal gland—is a precursor to testosterone. In women, the adrenal glands are the major, and sometimes only, the source of androgens. Elevated DHEA-S levels are associated with virilism (male body characteristics), hirsutism (excessive hair growth), amenorrhea (absence of menstruation), and infertility. Adrenal abnormalities such as tumours may lead to abnormally high DHEA-S levels.
Purpose of the Adrenal Hormone Tests
- To evaluate patients with suspected dysfunction of the adrenal glands
- To aid in the diagnosis and evaluation of adrenal abnormalities, such as Cushing’s syndrome, Addison’s disease, adrenal adenoma, or adrenal hyperplasia
- DHEA-S may be measured to determine the cause of hirsutism, amenorrhea, or infertility in women and to evaluate precocious puberty in children
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