ACTH test explained (AKTH)

ACTH is a hormone made by the pituitary gland — a gland that sits at the base of the brain. Its main function is to regulate how much cortisol (a glucocorticoid) the adrenal glands produce: when ACTH rises, the adrenal glands release more cortisol; when it falls, they release less. This chain (hypothalamus — pituitary — adrenal glands) governs the body's response to stress, its metabolism and inflammation.

Because ACTH and cortisol work in tandem, they are most often tested together — an ACTH value on its own, without cortisol, is hard to interpret. The amount of ACTH in the blood varies over the day: it is usually highest in the morning and lowest in the evening, so blood is taken at a set time, most often in the morning. The ACTH test helps to tell whether the cause of a disorder lies in the adrenal glands themselves, in the pituitary gland, or in brain structures above it.

• When a cortisol test result is outside the normal range and the reason needs to be established
• When there are signs of too much cortisol — weight gain, a rounded face, thin arms and legs, easy bruising, purple stretch marks, muscle weakness
• When there are signs of too little cortisol — persistent tiredness, muscle weakness, loss of appetite and weight, abdominal pain
• When a disease affecting the pituitary or the adrenal gland is suspected (Addison's disease, Cushing's disease or syndrome)
• To monitor the course of treatment of the pituitary or the adrenal glands

A raised ACTH is considered a possible sign of a pituitary or adrenal disorder according to MedlinePlus. Together with a low cortisol it is associated with Addison's disease (adrenal insufficiency), and together with a high cortisol — with Cushing's disease caused by a pituitary tumour or with a rare ACTH-producing tumour (ectopic Cushing's syndrome). A cortisol test and imaging tests help to establish the cause.

• Addison's disease — adrenal insufficiency (ACTH high, cortisol low)
• Cushing's disease — a pituitary tumour producing too much ACTH (ACTH and cortisol high)
• Ectopic Cushing's syndrome — a rare tumour elsewhere in the body that produces ACTH
• Congenital adrenal hyperplasia
• Multiple endocrine neoplasia type I

Symptoms that can accompany a raised ACTH

• Weight gain, especially around the waist
• A rounded face
• Thin arms and legs
• Easy bruising
• Purple stretch marks (striae)
• Muscle weakness

What to discuss with a doctor

• A cortisol test (in blood, saliva or urine) — together with ACTH it helps establish where the source of the disorder is
• Imaging tests (of the pituitary or the adrenal glands) at the doctor's discretion
• Whether steroid medicines that could affect the result are being taken
• When to repeat the test and at what time of day

A low ACTH is, according to MedlinePlus, associated with impaired pituitary function (hypopituitarism), the use of steroid medicines, or an excess of cortisol produced by an adrenal tumour, which suppresses ACTH production. Together with a low cortisol, a low ACTH indicates that the problem is most likely in the pituitary gland rather than in the adrenal glands.

• Taking steroid (glucocorticoid) medicines, which suppresses the natural production of ACTH
• Hypopituitarism — insufficient production of pituitary hormones
• An adrenal tumour producing too much cortisol and suppressing ACTH
• A natural response after a low-dose dexamethasone suppression test

Symptoms that can accompany a low ACTH

• Persistent tiredness
• Muscle weakness
• Loss of appetite
• Weight loss
• Abdominal pain

What is usually assessed with a low result

• A cortisol test and its assessment together with ACTH — this separates pituitary from adrenal causes
• Whether steroid medicines are being taken or were taken recently
• Additional tests assessing pituitary function at the doctor's discretion
• When to repeat the test to assess the change over time

Units, repeat testing and related indicators

For adults with blood taken in the morning MedlinePlus gives a range of 2-12 pmol/l, and in other units 9-52 pg/ml; an individual laboratory's range may differ depending on the time of day and the method used, so compare your result with the range printed on your own report. An ACTH value on its own, without cortisol, is hard to interpret, so a doctor assesses the two together and decides when, and at what time of day, to repeat the test. Related indicators: cortisol, cortisol in saliva, TSH, prolactin, parathyroid hormone, growth hormone, and also how to read blood test results.