ACTH blood test: purpose, preparation and results

Clinicians may request it when symptoms or other tests raise concern about unusually low or high cortisol production. The result does not establish a diagnosis by itself because hormone levels vary with time of day, illness, stress and certain medicines.

ACTH is made by the pituitary gland in the brain. It travels in the blood to the adrenal glands, where it stimulates cortisol release. Looking at ACTH and cortisol together helps a clinician judge whether an unusual hormone pattern may originate in the pituitary gland, the adrenal glands, or suppression from steroid medicine.

Laboratories use their own reference intervals, and the collection time matters because ACTH and cortisol follow a daily rhythm. A result marked high or low therefore needs interpretation against the sampling time, current symptoms, medicines and any recent steroid exposure.

Follow the requested appointment time and any fasting instructions from the clinic. Tell the clinician about tablets, injections, inhalers, nasal sprays and skin creams containing steroids, as well as hormone medicines. Do not stop prescribed steroids suddenly unless the prescribing clinician gives you a safe plan.

During collection, blood is taken from a vein. ACTH samples need careful handling, so attend the specified laboratory rather than changing the collection place without checking. Further testing may involve another cortisol sample or a stimulation or suppression test, depending on the pattern being investigated.

The blood draw itself usually needs only routine aftercare: apply pressure if the site oozes and seek advice if swelling, redness or increasing pain develops. Hormone-related symptoms can require faster help regardless of a pending test result.

Seek urgent medical care for severe weakness with repeated vomiting, confusion, fainting, marked drowsiness, or inability to keep fluids down. These symptoms may accompany dangerously low cortisol or another acute illness and should not wait for an outpatient result.

Ask whether cortisol was measured at the same time, whether the collection time and medicine list changed the interpretation, and if the test should be repeated. It is also useful to clarify whether an endocrinology review or a dynamic hormone test is the next step.