ACTH (adrenocorticotrophic hormone)

The range applies to a 9am sample (some labs print below 50 or 10 to 60 ng/L); afternoon and evening values are much lower, and it is always read alongside a cortisol taken at the same time.

ACTH is the pituitary hormone that instructs the adrenal glands to make cortisol. When cortisol is low the pituitary sends more ACTH, and when cortisol is high it sends less. Measuring both together tells doctors whether a cortisol problem starts in the adrenal glands or in the pituitary.

It is a specialist test requested when cortisol is found to be low or high, to work out where the problem lies. It is also used in the follow-up of pituitary conditions and in some people on long-term steroid medicines.

• Adrenal gland failure (Addison's disease), where cortisol is low
• A pituitary growth that makes ACTH (Cushing's disease)
• Rarely, tumours elsewhere that make ACTH
• Inherited adrenal enzyme conditions
• Stress, illness and early morning sampling

• Steroid medicines of any kind
• Adrenal tumours or nodules that make cortisol on their own
• Pituitary failure
• Afternoon or evening sampling

• It breaks down quickly in the tube, so a sample that was not chilled and separated promptly reads falsely low
• Time of day changes it several-fold
• Stress on the day of the test raises it

Usually a 9am sample, taken into a chilled EDTA tube, put on ice and separated within minutes, then frozen. Because of this it is often only done in hospital. A cortisol is taken at the same time.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.