ACTH (Adenocorticotropic Hormone)
Sample: Frozen EDTA plasma. Collect blood in the morning, in ice immersed EDTA tube. Separate EDTA plasma in refrigerated centrifuge and freeze immediately. Store frozen at -20°C in plastic tubes. Transport specimen to the laboratory in dry-ice following collection.
Schedule: Daily
Units: pg/mL
Range: Up 60 pg/mL
Remarks: ACTH (corticotropin) stimulates the adrenal cortices, which produce Cortisol. In Cushings syndrome, inappropriately increased ACTH stimulates the adrenal cortices to secrete excessive quantities of cortisol (ACTH-dependent Cushings syndrome), in which Cushings disease (pituitary ACTH-dependent adrenal cortical hyperplasia) or the ectopic ACTH syndrome is present.
In ACTH-independent Cushings syndrome, abnormal adrenal cortical tissue (adenoma, carcinoma, hyperplasia) suppresses secretion of both CRH and ACTH. The differential diagnosis of the obese, hirsute, hypertensive patient includes not only Cushings syndrome but cushingoid obesity. Partial deficiencies require dynamic tests such as the ACTH Stimulation test (Cosyntropin, Synacthen) and ACTH Suppression test. Urinary Free Cortisol is the test of choice for the separation of Cushings syndrome from entities, including obesity, which mimic it.
In primary adrenal insufficiency (Addisons disease) due to destruction of the adrenal glands by tumor, infection or immune mechanisms, ACTH plasma concentrations are elevated and cortisol levels are depressed. ACTH increases are found with congenital adrenal hyperplasia (adrenogenital syndrome).
In secondary adrenal insufficiency (secondary to pituitary insufficiency), ACTH and cortisol both are low. Causes of hypopituitarism include pituitary adenomas, craniopharyngioma, meningioma, other primary and metastatic tumors, postirradiation states, hemorrhage, infiltrative diseases (eg, eosinophilic granuloma) inflammation (eg, lymphocytic and granulomatous hypophysitis), and other disease entities.Concentrations of ACTH, TSH, FSH, LH, Growth Hormone, and of target organ hormones (eg, Thyroxine, Cortisol, Testosterone) are decreased.
