Adrenocorticotropic Hormone (ACTH)
ACTH is the pituitary's order to the adrenal glands to make cortisol. On its own the number means little. Paired with a cortisol that has already come back wrong, it points to where the fault sits.
Part of the Hormone Panel — see all 21 values together, including 17-Hydroxyprogesterone, Aldosterone, Androstenedione.
A light in the back room is out. Before changing anything, an electrician does one quiet thing: tests for power one junction back, at the breaker. If the breaker is still feeding the line, the fault is in the fixture. If the breaker is dead too, the fault is further up, at the panel. The dead bulb told you something is wrong. The reading taken one step upstream tells you where.
ACTH, adrenocorticotropic hormone, is that upstream reading. It is made by the pituitary gland at the base of the brain, and its one headline job is to tell the adrenal glands to release cortisol. So an ACTH result is rarely the first number anyone looks at. It earns its place on a report after a cortisol has already come back too high or too low, when the question is no longer is there a problem but which gland is causing it. Drawn by itself, ACTH is a breaker reading with no bulb to explain. Because ACTH is the upstream signal that switches the adrenal glands on, it is the trigger used in the stimulation test that confirms or rules out a backed-up 17-hydroxyprogesterone in suspected nonclassic CAH.
MedlinePlus puts the purpose plainly: the test helps find the cause of certain hormone problems, sorting pituitary causes from adrenal ones. That sorting only works as a pair. The cortisol says the light is out; the ACTH says where to look.
One practical note before the numbers. Like cortisol, ACTH keeps a daily rhythm and runs higher in the early hours, so MedlinePlus says providers usually ask for an early-morning draw and writes the reference values for that time. The morning serum range it gives is 9 to 52 pg/mL (roughly 2 to 12 pmol/L), so a value like 50 pg/mL sits at the upper edge of normal rather than past it. A draw taken at the wrong hour is hard to read against that band, which is why the timing instructions on the order tend to be exact.
How an ACTH value is usually read
pg/mLThe pituitary is sending the order loudly and the adrenal glands are not responding. This is the picture of primary adrenal insufficiency, the form that includes Addison's disease. The breaker is live; the fixture is the fault.
Cortisol is high because too much ACTH is driving it. MedlinePlus links this to a pituitary tumor overproducing ACTH (Cushing disease) or an ectopic ACTH-secreting tumor elsewhere. The fault sits at or before the panel, not in the adrenal glands.
The adrenal glands are making cortisol on their own, so the pituitary has stopped signalling and ACTH falls. MedlinePlus points to an adrenal tumor, or to steroid medicines, behind a suppressed ACTH. The fixture is stuck on with the breaker switched off.
Both numbers are down because the signal isn't being made. This is secondary adrenal insufficiency, a pituitary problem rather than an adrenal one. No power at the breaker, and the bulb dark for that reason.
An ACTH inside the morning band says little by itself. The figure is read against the cortisol drawn with it and the time of the draw, not as a stand-alone pass or fail.
No row of that grid reads down a single column. A high ACTH means one thing beside a low cortisol and the opposite beside a high one, which is why a lab rarely runs ACTH on its own.
What a high ACTH points to
A high ACTH means the pituitary is pushing hard, and the cortisol beside it says whether that is the body compensating or misfiring.
When cortisol is low and ACTH is high, the signal is reaching glands that cannot answer. The NIDDK describes this primary adrenal insufficiency, with Addison's disease as its best-known cause, and notes that the adrenal glands themselves are damaged or underactive. The pituitary, sensing too little cortisol, turns the order up, which is why ACTH climbs. The high reading is the breaker working correctly behind a broken fixture.
When cortisol is high and ACTH is also high, the order is the problem. The NIDDK identifies a pituitary tumor that overproduces ACTH, known as Cushing disease, as a cause of Cushing's syndrome, and MedlinePlus adds ectopic ACTH-secreting tumors elsewhere. In both, the excess cortisol is being driven rather than made independently, so ACTH stays up.
What a low ACTH points to
The meaning of a low ACTH is that the pituitary has gone quiet, and once again the cortisol beside it decides what that quiet implies.
When cortisol is high and ACTH is low, the adrenal glands are working without instruction. MedlinePlus connects a suppressed ACTH to an adrenal tumor producing cortisol on its own, and to glucocorticoid medicines doing the same job from outside the body. A normal feedback loop reads the high cortisol and shuts the order off, so ACTH drops. The fixture is lit with the breaker open.
What can suppress ACTH
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Glucocorticoid medicines
Steroid drugs taken for asthma, autoimmune disease, or after transplant act like cortisol, so the pituitary stops sending its own order. MedlinePlus names this as a cause of low ACTH; the effect includes inhalers, creams, and joint injections, not only tablets.
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An adrenal tumor making cortisol
A growth in an adrenal gland can produce cortisol independently, switching the pituitary signal off. Here a high cortisol sits beside the low ACTH.
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Pituitary underactivity
When the pituitary itself underproduces ACTH, both ACTH and cortisol run low together, the secondary form of adrenal insufficiency.
When cortisol is low and ACTH is low, the order is not being sent at all. The NIDDK calls this secondary adrenal insufficiency and locates the trouble in the pituitary rather than the adrenal glands. The distinction shapes what comes next, since the two forms are confirmed by different follow-up tests.
If an ACTH result came back with a flag
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1
Read it next to the cortisol, never alone
Ask your doctor which cortisol was drawn with this ACTH and at what hour. The same ACTH number means opposite things beside a high cortisol versus a low one, so a flag without its partner value is incomplete.
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2
Account for steroid medicines
Tell your doctor about any glucocorticoid use, including inhaled, topical, and injected forms. MedlinePlus names these as a cause of a suppressed ACTH, and they are easy to overlook.
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3
Expect a stimulation test, not a repeat draw
When adrenal insufficiency is the question, the NIDDK describes the ACTH stimulation test as the one used most often: an injection of man-made ACTH with cortisol measured before and 30 to 60 minutes after, to see whether the glands can respond. A baseline ACTH locates the problem; the stimulation test confirms it.
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4
Don't read one ACTH as a stress or fatigue score
ACTH is a diagnostic locator for cortisol disorders, not a wellness metric. A single value, outside the context of a cortisol result and a clinical question, rarely settles anything on its own.
Where ACTH fits on the panel
ACTH sits on the hormone panel as the partner to cortisol, and the two are almost always interpreted as a unit. The cortisol versus ACTH comparison walks through the pairing directly: cortisol is the adrenal output, ACTH the pituitary signal that drives it, and the relationship between them is what locates a disorder. The guide to reading a hormone panel covers how these endocrine values are read together rather than as isolated flags.
Two other markers travel in ACTH's orbit. DHEA-S is a second adrenal steroid that also depends on ACTH to be produced, so it can fall when the pituitary signal does. And because cortisol nudges blood sugar upward, a glucose drawn during a cortisol disorder can read off in ways that make more sense once the ACTH picture is clear. ACTH keeps a daily rhythm the way TSH does, one more reason the draw time is part of the result. When a pituitary problem is on the table, ACTH is usually read next to its neighbors from the same gland, including IGF-1, the steady downstream proxy for growth hormone.
Read in context and confirmed with timed testing, a single ACTH is one frame in a workup, not a verdict. Since the same number means opposite things beside a high cortisol versus a low one, reading the two results against each other is the whole skill, not interpreting either figure on its own.
Sources
- ACTH (Blood Test) — MedlinePlus, National Library of Medicine
- Adrenal Insufficiency & Addison's Disease — NIDDK, National Institutes of Health
- Diagnosis of Adrenal Insufficiency & Addison's Disease — NIDDK, National Institutes of Health
- Cushing's Syndrome — NIDDK, National Institutes of Health
Written and reviewed by BloodSight Editorial Team · Last updated
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Normal ranges
| Group | Range | Unit |
|---|---|---|
| Adult Male | 9–52 | pg/mL |
| Adult Female | 9–52 | pg/mL |
Reference ranges may vary by laboratory and individual factors.
Adrenocorticotropic Hormone — Common Questions
What is a normal ACTH level?
Why is ACTH tested together with cortisol?
What does a high ACTH level mean?
What does a low ACTH level mean?
Why does ACTH have to be drawn in the morning?
What is the ACTH stimulation test, and is it the same blood test?
Disclaimer
This content is for informational and educational purposes only. It is not intended as medical advice, diagnosis, or treatment recommendation. Reference ranges may vary by laboratory. Always discuss your results with a qualified healthcare professional.
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