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ACTH (Adrenocorticotropic Hormone)

A pituitary hormone that tells the adrenal glands to make cortisol. It is read together with cortisol to see where a hormone problem may start.

AI-verified against cited sources. Awaiting expert reviewAlso called ACTHLOINC 2141-0

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What it is

ACTH (adrenocorticotropic hormone) is made by the pituitary gland at the base of the brain. It tells the adrenal glands to make cortisol. When cortisol is low, the pituitary makes more ACTH, and when cortisol is high, it makes less. ACTH is released in short pulses and follows a daily rhythm, with the highest levels in the morning and the lowest in the evening. It also breaks down quickly in a blood tube, so the sample needs careful handling.

Why it matters

ACTH helps show whether a cortisol result starts in the adrenal glands or in the pituitary. For example, low cortisol with a high ACTH is linked to the adrenal glands, while low cortisol with a low ACTH is linked to the pituitary or the brain's control center. High cortisol with a low ACTH is linked to the adrenal glands acting on their own. Because the number changes during the day and with stress, it is almost always read next to a cortisol drawn at the same time. The Endocrine Society does not recommend ACTH as a first test when Cushing syndrome is the question.

If it’s low

A low ACTH is often explained by steroid medicines, which tell the pituitary to make less ACTH, or by a sample drawn late in the day when ACTH is normally lower. Less often, it reflects a pituitary problem (usually with low cortisol) or an adrenal gland that makes cortisol on its own (with high cortisol). Clinicians read it together with cortisol.

Common causes

  • Steroid medicines taken by mouth or by injection
  • A sample drawn in the afternoon or evening, when morning ranges don't apply
  • A sample that waited too long, or sat in the wrong tube, before it was frozen
  • Low cortisol from a pituitary or hypothalamus problem (secondary adrenal insufficiency)
  • An adrenal tumor or overactive adrenal tissue that makes cortisol on its own

What can help

  • Tell your clinician about every steroid medicine you take or recently stopped, including injections
  • Ask whether the test should be repeated in the morning at the same lab
  • Ask which other tests would help explain it

If it’s high

A high ACTH is read next to cortisol. ACTH rises when the body is trying to raise a low cortisol, as when the adrenal glands aren't responding. It can also be high simply because the sample was drawn near the morning peak, or during stress, pain or illness. Less often, a pituitary tumor or another tumor makes too much ACTH and drives cortisol up. One result can't tell these apart, so clinicians usually add a cortisol, repeat the test or order others.

Common causes

  • A sample drawn near the morning peak
  • Physical or emotional stress, pain or acute illness
  • Low cortisol because the adrenal glands aren't responding (primary adrenal insufficiency, including Addison disease)
  • Congenital adrenal hyperplasia, where cortisol production is blocked
  • A lab method that also reads ACTH fragments or related molecules
  • A pituitary tumor that makes ACTH (Cushing disease), which is uncommon
  • A tumor outside the pituitary that makes ACTH (ectopic ACTH), which is rare

What can help

  • Ask how your ACTH compares with a cortisol drawn at the same time
  • Ask whether the draw time and sample handling met your lab's instructions
  • Tell your clinician about steroid medicines, biotin and other supplements

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

We don’t have a usual range for adults.

What can affect your result

  • Time of day: highest in the morning, lowest in the evening
  • Stress, pain, illness and physical effort
  • Steroid medicines, which lower it
  • How the sample was handled: it needs the right tube and prompt processing and freezing
  • The assay: different immunoassays can give different numbers, especially at low levels
  • Handling: ACTH breaks down quickly in the tube. Labs ask for EDTA plasma in a plastic or siliconized tube that is separated promptly and frozen, and some ask for the tube to be chilled. A delay or the wrong tube can give a falsely low result.
  • High-dose biotin (vitamin B7) can interfere with some assays, so tell your lab if you take it and ask whether to pause it before the draw.
  • In rare cases, antibodies to mouse proteins (heterophile antibodies) or very high antibody levels distort an immunoassay result.
  • Immunoassays can be thrown off by ACTH fragments, precursor molecules and synthetic ACTH such as cosyntropin, in either direction depending on the assay.
  • Steroid medicines taken by mouth or injection lower ACTH.
  • ACTH is released in pulses, so a single sample is a snapshot. Stress, pain, illness and exercise can raise it.

Morning, between about 7 and 10 a.m. Reference ranges apply to morning samples only. Changes within hours. ACTH is released in pulses and clears from the blood quickly, so one sample shows the moment of the draw.

When to talk to a clinician

Contact the clinician who ordered the test if your lab flagged the result. Seek urgent care for severe weakness, fainting, repeated vomiting, severe belly pain or confusion, especially if you take or recently stopped steroid medicines. If you feel very unwell, call 911 or your local emergency number.

Questions you could ask

  • What other tests would help explain my ACTH and cortisol results?
  • Was my cortisol measured at the same time as my ACTH?
  • Could stress, illness or the way the sample was handled have affected this result?
  • Could a steroid medicine I take or recently stopped explain this result?
  • Should we repeat the test in the morning at the same lab?

Questions people ask

Why does my lab only give a range for morning samples?

ACTH follows a daily rhythm, with its peak in the morning. Labcorp and ARUP set their range using samples drawn between 7 and 10 a.m., and ARUP says no range has been set for afternoon samples. A later sample can't be judged against the morning range.

Why is cortisol usually measured at the same time?

ACTH and cortisol work as a pair. Cortisol tells the pituitary how much ACTH to make, so each number is easier to read next to the other. Ask your clinician whether both were drawn together.

How do I convert pg/mL to pmol/L?

Multiply pg/mL by 0.2202, so 20 pg/mL is about 4.4 pmol/L. To go the other way, multiply pmol/L by 4.541. A value in ng/L is the same number as pg/mL.

Show the science and sources

Units

  • 1 pg/mL = 1 pg/mL
  • 1 pg/mL = 0.2202 pmol/L
  • 1 pg/mL = 1 ng/L

Open the ACTH unit converter

For clinicians and researchers

ACTH(1-39) is a 39-amino-acid peptide cleaved from pro-opiomelanocortin (POMC) in the anterior pituitary (molecular weight about 4,541). Release is pulsatile with a diurnal rhythm (morning peak, evening trough), and plasma clearance is rapid, so one value is a snapshot. ACTH degrades quickly in the tube: labs specify EDTA plasma in plastic or siliconized glass, with prompt separation and freezing. Sandwich immunoassays (for example Roche ECLIA) measure intact ACTH 1-39 and can be affected by high-dose biotin, heterophile and anti-mouse antibodies, and by ACTH fragments, precursors and synthetic analogs. Assays are not standardized or harmonized, and reference intervals are for morning draws only. Interpretation: in people with confirmed cortisol deficiency, a plasma ACTH more than 2 times the upper reference limit is consistent with primary adrenal insufficiency (Endocrine Society 2016, rec 2.4). The 2008 Endocrine Society Cushing guideline recommends against random serum cortisol or plasma ACTH as an initial test (rec 3.5). Once hypercortisolism is confirmed, ACTH below about 5 pg/mL favors an ACTH-independent (adrenal) cause and above about 20 pg/mL an ACTH-dependent cause, with 5 to 20 a gray zone (ADLM CLN 2021). Conversion: pg/mL × 0.2202 = pmol/L.

LOINC 2141-0 (primary), 14674-6, 56913-7, 51696-3. Specimen: plasma.

Sources

  1. Adrenocorticotropic Hormone (ACTH), Plasma (test 004440), Labcorp
  2. Adrenocorticotropic Hormone (ACTH) (test 0070010), ARUP Laboratories
  3. Adrenocorticotrophic Hormone (ACTH), Oxford University Hospitals NHS Foundation Trust, Biochemistry tests catalogue
  4. Plasma ACTH: Tales of Diagnostic Misadventure and the Path Forward, Clinical Laboratory News (ADLM) (2021)
  5. Diagnosis and Treatment of Primary Adrenal Insufficiency: An Endocrine Society Clinical Practice Guideline, Journal of Clinical Endocrinology & Metabolism (2016)
  6. The Diagnosis of Cushing's Syndrome: An Endocrine Society Clinical Practice Guideline, Journal of Clinical Endocrinology & Metabolism (2008)
  7. Corticotropin (PubChem CID 16132265), NCBI PubChem

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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