ACTH (Adrenocorticotropic Hormone) is a chemical messenger produced by your pituitary gland, a pea-sized master gland located at the base of your brain. Its primary job is to tell your adrenal glands (which sit on top of your kidneys) when to produce and release cortisol, your body's main stress hormone.
Think of ACTH as a biological thermostat. When cortisol levels in your bloodstream drop below normal, your brain senses it and releases more ACTH to turn cortisol production back up. When cortisol levels rise too high, your brain scales back its ACTH production to keep things balanced.
Doctors usually order an ACTH test to help find the root cause of abnormal cortisol levels. Evaluating them together helps determine if a hormonal problem originates in the brain (pituitary gland) or directly in the adrenal glands.
Like cortisol, ACTH levels change significantly throughout the day. They peak in the early morning hours and reach their lowest point around midnight. Because of this natural diurnal cycle, an afternoon or evening blood draw will look completely different from a morning draw.
Reference ranges can vary considerably depending on the specific laboratory analyzing your sample. Always compare your final score to the baseline range listed on your physical lab report.
ACTH samples are almost always collected between 7 AM and 10 AM, alongside a morning cortisol test. Because the molecule breaks down rapidly in a test tube, the blood must be chilled immediately after being drawn to ensure accurate measurement.
Elevated ACTH levels may reflect an overproducing pituitary gland (Cushing's disease), tumors outside the brain releasing the hormone, or primary adrenal failure (Addison's disease) where the brain is overcompensating for failing kidneys.
Low ACTH levels often suggest an underactive pituitary gland (hypopituitarism) or a cortisol-producing adrenal tumor that is telling the brain to turn off ACTH production entirely. Recent use of steroid medications can also drive this down.
Because ACTH directly drives cortisol levels, the symptoms are closely tied to cortisol imbalances:
An elevated ACTH level can stem from several distinct medical scenarios. If your adrenal glands are damaged or destroyed by an autoimmune response (Addison's disease), they cannot produce cortisol. The brain responds by pumping out massive amounts of ACTH to jumpstart them.
Alternatively, a benign tumor on the pituitary gland itself can overproduce ACTH (known as Cushing's disease). In rare cases, certain tumors outside the brain, such as small cell lung cancers, can produce ACTH independently (ectopic ACTH production). Severe physical trauma, major surgery, and intense emotional stress can also trigger temporary spikes.
The most common cause of a suppressed ACTH level is the use of prescription corticosteroid drugs (like prednisone or dexamethasone). When you take these medications, your brain confuses them for natural cortisol and halts ACTH production.
If you aren't taking steroids, low ACTH can point toward a pituitary gland that is struggling to generate hormones due to injury, a tumor, or surgical damage (hypopituitarism). It can also occur if an autonomous tumor inside an adrenal gland is overproducing cortisol independently, causing a negative feedback mechanism that shuts down the brain's ACTH production.
ACTH readings require clinical context. Your physician will frequently compare your data against:
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