Adrenocorticotrophic hormone (ACTH) is a 39 amino acid peptide hormone secreted by the anterior pituitary, under the control of the hypothalamic peptide, corticotrophin-releasing hormone (CRH). ACTH secretion is pulsatile and exhibits diurnal variation, with highest plasma concentrations around 8am and lowest levels at midnight. It stimulates glucocorticoid (cortisol) production in the adrenal cortex.

ACTH measurement is only useful as a second line investigation following the finding of either cortisol deficiency or excess.

In cortisol deficiency due to primary adrenal failure, ACTH will be raised due to lack of negative feedback. ACTH will be low in adrenal insufficiency secondary to pituitary failure (hypopituitarism).

Excessive production of cortisol accompanied by suppressed ACTH may be seen in Cushing's syndrome due to adrenal tumours/hyperplasia, and with exogenous glucocorticoid administration.
Cortisol excess with raised ACTH may be seen in ACTH-producing tumours of the pituitary (Cushing's disease) or other tissues e.g. lungs (ectopic ACTH production).

NB. ACTH secretion may be increased by stress.

Sample Requirements and Reference Ranges

Sample type	Plasma
Container	EDTA
Precautions	Separate and freeze plasma within 30 minutes of sample collection. Transport frozen. Timing of collection important. Avoid stress. Haemolysed specimen unsuitable.
Minimum volume	1 mL
Reference range	Not applicable
Turnaround time	7 days
Method	Siemens Immulite