ACTH: what it is, what it tells you and when it’s tested

ACTH, or corticotropin, is a hormone made by the pituitary, a small gland at the base of the brain. It tells the adrenal glands to make cortisol. When cortisol is low, ACTH rises; when it is high, ACTH falls. That is why the two are always read together.

When it’s tested

Doctors order it when cortisol is out of place and they need to know why. If cortisol is low, ACTH shows whether the problem is in the adrenal glands or the pituitary. If cortisol is too high, it shows where the excess starts.

It is also used to follow people with a pituitary or adrenal condition, often with an endocrinologist.

It is not a test for people who feel well: on its own it says nothing, and the sample is delicate. Rosa does not test it. It does look at sodium, potassium and blood sugar, which shift when the cortisol system is not working.

What it tells you, and what it does not

Low cortisol and high ACTH: the adrenal glands make too little, for example in Addison’s disease. The pituitary pushes, but the adrenals do not respond.

Low cortisol and low or normal ACTH: the problem starts in the pituitary, or steroid medicines are holding it back.

Too much cortisol with high or normal ACTH: the excess is driven by ACTH, usually from a small benign pituitary tumour. Too much cortisol with low ACTH: the excess comes from an adrenal gland.

That is why it is read together with other tests:

• Cortisol: Without cortisol, ACTH cannot be read
• Sodium: Falls when cortisol is short
• Potassium: Rises when the adrenal glands make too little
• Blood sugar: Shifts with cortisol, up or down

Normal ACTH levels

Normal levels vary a lot from one method to another. A large Italian hospital lab gives 10 to 55 pg/mL in the morning. With another widely used method, healthy adults sit between 7.2 and 63 pg/mL. The range on your own report is what counts.

ACTH is highest early in the morning and lowest in the evening, and it rises and falls in waves during the day too. That is why the test is done in the morning, usually with cortisol.

A result outside the range is not a diagnosis on its own. It is read with the cortisol from the same sample.

If your ACTH is high or low

• High ACTH: With low cortisol it points to the adrenal glands. With high cortisol, to the pituitary. Sudden stress and a difficult blood draw also raise it.
• Low ACTH: Often down to steroid medicines. With low cortisol it points to the pituitary, with high cortisol to an adrenal gland.

What can skew the result

ACTH is a fragile hormone. The result depends a lot on how and when the blood is taken.

• A tube that is not chilled: ACTH breaks down quickly. The tube must be kept cold and taken to the lab straight away, or the value falls.
• The time of the test: It is highest early in the morning. A test taken late can look low.
• Steroid medicines: Tablets, inhalers, creams or joint injections hold back the pituitary and lower ACTH. Do not stop them on your own.
• Sudden stress and illness: Severe pain, an illness or a difficult blood draw raise it briefly.

When to worry

Talk to your doctor if:

• Your ACTH is outside the range and the cortisol from the same sample is too.
• You have been tired for weeks, are losing weight, feel dizzy when you stand, crave salt or have darker skin without sun.
• You have headaches that do not go away or see less at the sides of your vision: these can come from the pituitary.
• You have extreme weakness, vomiting that will not stop, severe tummy pain, fainting or confusion: call 112 or go to the emergency department.

Frequently asked questions

What are normal ACTH levels? It depends a lot on the method. A large Italian hospital lab gives 10 to 55 pg/mL in the morning. The range on your report is what counts, and the result is read with cortisol.

How is the ACTH sample taken? In the morning, usually with cortisol. The blood goes into a special tube, kept cold and taken to the lab straight away. Follow your lab’s instructions on fasting and timing.

What do high ACTH and low cortisol mean? That the pituitary pushes but the adrenal glands respond poorly. It can be primary adrenal insufficiency, such as Addison’s disease. It needs a visit soon, often with an endocrinologist.

What do low ACTH and high cortisol mean? That the extra cortisol does not come from the pituitary. Your doctor usually looks for a cause in the adrenal glands, with other tests.

Does Rosa test ACTH? No. Rosa measures sodium, potassium and blood sugar, which shift when the cortisol system is not working. If your doctor wants ACTH, they order it separately.

Sources

• Bornstein and colleagues, diagnosis and treatment of primary adrenal insufficiency: an Endocrine Society clinical practice guideline. Journal of Clinical Endocrinology and Metabolism, 2016. PMID 26760044
• Fleseriu and colleagues, consensus on diagnosis and management of Cushing’s disease: a guideline update. Lancet Diabetes and Endocrinology, 2021. PMID 34687601
• Verschraegen and colleagues, multicenter evaluation of a rapid electrochemiluminescent adrenocorticotropic hormone (ACTH) immunoassay. Clinica Chimica Acta, 2007. PMID 17321508
• Fondazione Policlinico Universitario A. Gemelli IRCCS, clinical chemistry laboratory: list of tests and reference intervals, 2024. Policlinico Gemelli, elenco prestazioni CDS.002