ACTH

Has your doctor measured your cortisol and found an abnormal result? ACTH (adrenocorticotropic hormone) is a pituitary hormone that signals the adrenal glands to produce cortisol. Interpreted alongside cortisol and additional endocrine tests, ACTH helps clarify the cause of a disorder. When excess cortisol is suspected, other tests first confirm that there really is too much; further investigations then identify the cause.

Who is this test for

• people with low morning cortisol or signs of deficiency: persistent fatigue, weakness, weight loss, low blood pressure, salt craving and darkening of the skin;
• when there are signs of excess cortisol: weight gain around the trunk and face, wide purple stretch marks, easy bruising, high blood pressure and blood sugar;
• people with pituitary disease or after surgery or radiotherapy in that area;
• after prolonged corticosteroid use, when a doctor is assessing recovery of natural cortisol secretion;
• to monitor treatment of adrenal gland disease.

Severe weakness, vomiting, abdominal pain, very low blood pressure and confusion in someone with adrenal disease are an emergency: call 194 or 112 immediately.

What the test reveals

The pituitary gland secretes ACTH, which stimulates the adrenal glands to produce cortisol. When there is enough cortisol, the pituitary reduces ACTH secretion. When the adrenal glands work poorly, ACTH rises as the pituitary tries to stimulate them. When the pituitary works poorly, ACTH is low, as is cortisol.

ACTH has a daily rhythm: it is highest in the morning and lowest around midnight. The result is therefore always read alongside the sampling time and cortisol from the same sample.

The test and preparation

A venous blood sample is taken. Come in the morning, between 7 and 10, well rested; ideally, cortisol should be sampled at the same time. Fasting is not required. Stress, acute illness and a sleepless night can increase ACTH.

Bring a list of medicines, including corticosteroid tablets, inhalers, nasal sprays and creams. Do not stop treatment yourself, because stopping suddenly may be dangerous. If you take biotin (e.g. hair and nail supplements), tell us at blood collection, and also mention if you work night shifts. Blood collection takes a few minutes.

What your results mean

• High ACTH with low cortisol suggests impaired function of the adrenal gland itself (primary insufficiency, for example Addison’s disease).
• Low or borderline-normal ACTH with low cortisol suggests reduced pituitary function or secretion suppressed by corticosteroids.
• Low ACTH with confirmed cortisol excess usually means that the excess cortisol originates from the adrenal gland or medication.
• Normal or high ACTH with confirmed cortisol excess suggests the pituitary (Cushing’s disease) or, more rarely, a tumour outside the pituitary that produces ACTH.

A single result does not establish a diagnosis. Reference values are printed on the report, and a doctor, usually an endocrinologist, interprets it and may request stimulation or suppression tests and imaging.

How to arrange testing

You can come for blood collection without an appointment or referral at one of our branches throughout Croatia (listed on the Contactpage). Prices for all tests and panels are listed in the price list. On arrival, say that you also want cortisol so that both tests can be sampled at the same time.

Frequently asked questions

Should ACTH be sampled together with cortisol?

Yes. ACTH alone is difficult to interpret. Cortisol from the same sample helps a doctor assess the cause of a disorder, and additional endocrine tests are often needed for a definitive answer.

Why is ACTH sampled in the morning?

Because of its daily rhythm: it is highest in the morning. A sample taken later in the day is difficult to compare with reference values.

Do corticosteroids affect the result?

Yes. Prolonged use of corticosteroid tablets, inhalers, sprays or creams lowers ACTH and cortisol. Only a doctor decides whether to pause treatment.

Is an ACTH test the same as an ACTH stimulation test?

No. This test measures your own ACTH in blood. In a stimulation test, ACTH is injected and the rise in cortisol is monitored; an endocrinologist refers you for it.