Adrenocorticotropic Hormone (ACTH), Plasma
Pituitary function test useful in the differential diagnosis of Cushing syndrome, ectopic ACTH syndrome (eg, carcinoma of lung, islet cell tumors, carcinoid tumors, medullary carcinoma of thyroid), Addison disease, hypopituitarism, and ACTH-producing pituitary tumors (eg, Nelson syndrome)
Additional Teast Information:
Adrenocorticotropic hormone (ACTH), or corticotropin, is a peptide hormone consisting of 39 amino acids. It is produced in the anterior pituitary of the brain as part of the precursor molecule pro-opiomelanocortin (POMC). Tissue-specific cleavage results in ACTH and a range of related peptides.1,4ACTH stimulates formation and secretion of glucocorticoids (especially cortisol) by the adrenal cortex. The glucocorticoid production is regulated by various factors.5-8 After stimulation (eg, by physical effort or by the internal body clock), the hypothalamus secretes CRH (corticotropin-releasing hormone). CRH acts on the pituitary, which in turn synthesizes and secretes ACTH. Finally, ACTH stimulates secretion of the glucocorticoids by the adrenals. High concentrations of glucocorticoids in the blood inhibit secretion of CRH and ACTH via a negative feedback mechaniACTH concentrations show a diurnal variation with high levels in the morning and low levels in the evening; therefore, as with cortisol, it is important to know the collection time of the plasma sample for interpretation of the results.Plasma ACTH measurements are useful in the differential diagnosis of pituitary Cushing’s disease (ACTH hypersecretion), autonomous ACTH-producing pituitary tumors (eg, Nelson’s syndrome), hypopituitarism with ACTH deficiency, and ectopic ACTH syndrome.9,10 In addition to cortisol measurements, ACTH determinations can be used together with functional or stimulation tests to diagnose the origin of glucocorticoid overproduction. Similarly, ACTH measurements can be employed to facilitate differential diagnosis of adrenocortical insufficiency (Addison’s diseaseACTH not produced by the pituitary gland is known as ectopic ACTH;11 this is often associated with small cell carcinoma of the lung. In rare cases, ectopic ACTH can be caused by thymic tumors, pancreatic adenocarcinomas, or bronchial carcinoids. These tumors often secrete ACTH precursors (POMC and pro-ACTH).
Plastic or siliconized glass lavender-top (EDTA) tube
ACTH should be drawn between 7 AM and 10 AMCollect into iced plastic or siliconized glass lavender-top (EDTA) tube, noting time of collection. After venipuncture, immediately immerse the tubes in an ice bath. Separate plasma from cells by centrifugation within one hour after venipuncture.1,2 Transfer the plasma into a transpak frozen purple tube with screw cap immediately. Freeze immediately and maintain frozen until tested. To avoid delays in turnaround time when requesting multiple tests on frozen samples, please submit separate frozen specimens for each test requested.
Thawed specimen; serum or heparinized plasma specimen; specimen collected in nonsiliconized glass tube