ACTH

ACTH (adrenocorticotropic hormone) is made in the pituitary gland, a hormone gland below the brain. It prompts the adrenal glands to make cortisol. Normally, ACTH rises when there is too little cortisol and falls when there is too much. Like cortisol, ACTH has a daily rhythm: it is highest early in the morning and lowest at night.

• Where the cause lies when cortisol is too low: in the adrenal gland itself (Addison's disease, with a high ACTH) or in the pituitary gland (with a low ACTH)
• Where the cause lies when cortisol is too high: an ACTH-producing tumor, usually a benign tumor of the pituitary gland (Cushing's disease), or the adrenal gland itself
• Suppression of the pituitary and adrenal glands by the use of corticosteroids

• Have your blood taken between 8.00 and 10.00, because ACTH drops during the day.
• Avoid stress and heavy exercise shortly before the sample is taken.

The GP assesses ACTH together with a cortisol value from early in the morning and asks about the use of corticosteroids. With a low cortisol and a high or, on the contrary, low ACTH, referral follows to an endocrinologist (internist specializing in hormones), usually for a stimulation test. With a high cortisol and matching symptoms, tests that confirm the excess come first, followed by imaging of the pituitary or adrenal glands.

ACTH is not a screening test: the value can only be assessed together with a cortisol value from the same moment. The Dutch Society for Clinical Chemistry (NVKC) calls the interpretation of ACTH and cortisol results complex, because both hormones vary strongly over the day. ACTH is mainly meaningful after a too high or too low cortisol has been found: the value then shows where the cause lies. In people without symptoms, a single ACTH value says little, and the value says nothing about stress or 'adrenal fatigue'.

• Timing: ACTH is highest early in the morning; only a sample taken at a fixed time can be compared with the reference values.
• The sample must be cooled and processed quickly; ACTH breaks down quickly in blood, which can give a result that is too low.
• Corticosteroids in any form lower ACTH; stress around the sample collection, pain and illness raise it temporarily.
• Reference values differ per laboratory and measurement method; biotin supplements can interfere with some measurement methods.

Adrenal and pituitary disorders are rare. Addison's disease is estimated to occur in 40 to 115 per million inhabitants, and Cushing's syndrome due to a tumor is diagnosed in about 50 people a year in the Netherlands. Much more often, an abnormal ACTH is the result of using corticosteroids.

Useful if a too low or too high cortisol has been found or is strongly suspected, to determine whether the cause lies in the pituitary gland or in the adrenal gland, and in people with a known pituitary disorder. As a stand-alone test, without cortisol from the same sample, ACTH has little value. Not useful with tiredness or stress without other symptoms: the result is then almost always normal or cannot be interpreted.

• An abnormal value due to the timing, stress or a sample that was not stored properly can cause unnecessary worry about the pituitary or adrenal glands and unnecessary follow-up testing.
• A single ACTH result without a cortisol value cannot be interpreted and can wrongly reassure or alarm.

• NVKC, allesovertesten.nl: ACTH
• Huisartsenbrochure Bijnierziekten (Bijniervereniging NVACP, via NHG)
• Maastricht UMC+, afdeling Endocrinologie: Syndroom van Cushing
• Maastricht UMC+, afdeling Endocrinologie: Hypofyse-uitval