Endocrine markers complementing routine diagnostics of Adrenal Function
The fully automated Immunodiagnostic Systems panel for Adrenal Function now includes the IDS ACTH, Cortisol, Urinary Cortisol and Salivary Cortisol assays for use on the IDS systems.
The adrenal cortex has three distinct zones which secrete various hormones under the direct control of specific feedback mechanisms 1. Cortisol secretion from the adrenal glands’ zona fasciculata is primarily regulated by corticotropin, also known as adrenocorticotropic hormone, or ACTH. ACTH is released from the anterior pituitary in response to hypothalamic neuropeptides and stress 1, 2 .
ACTH and cortisol measurements are frequently used in the assessment of adrenocortical function and other disturbances of the hypothalamic-pituitary-adrenal (HPA) axis.
These include the screening and differential diagnosis of Cushing’s syndrome (CS), a large group of signs and symptoms due to prolonged and inappropriately high exposure to glucocorticoids, mainly cortisol 3. Many common signs of Cushing’s such as obesity, high blood pressure, and increased blood glucose are frequently observed today 4. In general, normal or high ACTH concentrations indicate pituitary or ectopic sources of ACTH, while low concentrations indicate an adrenal tumour secreting glucocorticoids 5. For the initial testing of CS, the Endocrine society recommends the following screening tests6: Urine free cortisol (UFC), late-night salivary cortisol, and the dexamethasone suppression test (DST). For UFC, levels below the upper limit of normal are considered a normal response7, while a cut-off at <1.8ug/dL is an indication of suppressed serum levels during the DST. Late-night saliva concentrations in healthy subjects should be at <0.1 to 0.2ug/dL8.
ACTH and cortisol levels also play a role in the diagnosis of Addison’s disease, a failure of the adrenal gland to produce cortisol. Patients with primary adrenal insufficiency (AI) can be diagnosed based on a combined measurement of early morning serum cortisol and plasma ACTH levels. The Endocrine Society recommends that a peak cortisol <18 µg/dL following a standard-dose corticotropin stimulation test is indicative of adrenal insufficiency 1, 6. Secondary AI most commonly requires dynamic testing such as the insulin tolerance test or the overnight metyrapone test 1,8,9.