ACTH, Plasma

ACTH

211

1.5 mL frozen plasma collected in an EDTA (lavender-top) tube

0.5 mL

Collect specimens between 7 a.m. and 10 a.m. If drawn during any other time, the reference ranges do not apply.

Only use pre-chilled EDTA tube. After drawing the blood, put the tube immediately on ice. Centrifuge immediately to separate the plasma. Plasma should be transferred to a pre-chilled plastic transport container and frozen immediately.

Frozen

Room temperature: Unacceptable
Refrigerated: Unacceptable
Frozen: 32 days

Plasma other than EDTA plasma

Set up: Mon-Sat; Report available: Same day after receipt at the performing laboratory. Add two (2) days for transport.

With patients receiving more than 5mg/day of biotin, a sample should be taken no sooner than eight hours after previous dose. Patients treated with monoclonal mouse antibodies may have inaccurate results. High titer of antibodies such as streptavidin and ruthenium may cause interference. Due to its correlation with cortisol levels, ACTH concentration is affected by stress. Any single measure may be within the reference range for patients with increased production (Cushing's disease) or minimal production of ACTH.

7.2-63.3 pg/mL

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 relatedpeptides. ACTH stimulates formation and secretion of glucocorticoids (especially cortisol) by the adrenal cortex.

Glucocorticoid production is regulated by various factors. After stimulation (e.g. 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 glucocorticoids by the adrenals. High concentrations of glucocorticoids in the blood inhibit secretion of CRH and ACTH via a negative feedback mechanism.

ACTH 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 Cushing's disease (ACTH hypersecretion), autonomous ACTH producing pituitary tissue (e.g. Nelson's syndrome), hypopituitarism with ACTH deficiency and ectopic ACTH syndrome. In addition to cortisol measurements, ACTH determinations can be used together with suppression 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 disease).

ACTH not produced by the pituitary gland is known as ectopic ACTH; 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).