ACTH (Adrenocorticotropic Hormone)
The pituitary hormone that signals the adrenal glands to produce cortisol.
Separates adrenal from pituitary causes of abnormal cortisol — exactly like LH/FSH does for testosterone. Essential for interpreting a high or low cortisol.
ACTH is only interpretable against the cortisol drawn at the same moment, and the pairing is the entire point: high cortisol with high ACTH points at the pituitary, high cortisol with suppressed ACTH at the adrenal, low cortisol with high ACTH at primary adrenal failure, low with low at the pituitary. An ACTH number alone answers none of those. It is also one of the most fragile analytes in the lab — pulsatile, strongly diurnal, and degraded by proteases at room temperature, so it needs a chilled EDTA tube spun cold and frozen. A mishandled ACTH reads falsely low, which is the direction most likely to be misread as reassuring.
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What ACTH (Adrenocorticotropic Hormone) actually measures — the analyte, and the assay
The analyte is ACTH 1–39, a 39-residue peptide of about 4.5 kDa cut out of pro-opiomelanocortin by prohormone convertase 1. The same precursor also yields beta-lipotropin and beta-endorphin, and in some tumors the precursor itself circulates — so the tube contains a family of related peptides and the assay has to pick one of them.
Method: a two-site immunometric assay in which one antibody binds near the N-terminus and the other near the C-terminus, so only an intact molecule bridges the pair. Different manufacturers choose different epitopes, which is why they differ in how much precursor and fragment they count — and why an ACTH result is not portable between platforms Haddad 2019.
That is not theoretical. It has a documented case. A patient's ACTH came back at 113.0 pg/mL on a Siemens Immulite assay, inconsistent with the clinical picture; run on a CIS Bio ELSA-ACTH assay, the same patient's ACTH was normal, and the published conclusion was that diagnostic criteria should outrank an assay result when the two disagree Yang 2022. Sandwich assays fail upward through heterophile and anti-reagent antibodies bridging the two antibodies directly Ghazal 2022.
Two more properties of the molecule set the rest of the page. ACTH travels with no carrier protein, so unlike cortisol it has no buffered reservoir and its concentration is whatever the corticotroph released a few minutes ago. And it is cleared far faster than the cortisol it drives, which is why the two have to come out of the same needle at the same minute rather than an hour apart — a mismatched pair is one of the recognized technical pitfalls in reading endocrine tests Haddad 2019.
Then there is the tube, which on this marker is not a footnote. ACTH is a small peptide with no binding protein to shield it, and plasma proteases degrade it at room temperature. It needs a chilled EDTA tube, prompt cold centrifugation and frozen plasma; specimen handling, tube additive and anticoagulant sit near the top of the published causes of preanalytical immunoassay error Caruso 2020. A mishandled ACTH reads falsely LOW — the direction most easily mistaken for reassurance, and the direction that turns primary adrenal insufficiency into a normal report.
ACTH (Adrenocorticotropic Hormone): what changes the blood, and what only changes the reading
What changes the ACTH in your blood:
- The time of day, by more than any pathology on this list. ACTH follows a steep circadian curve with an early-morning peak and a late-evening trough. An afternoon value read against a morning reference interval is a different measurement wearing the same units.
- Pulse timing. Corticotroph release is episodic, so two samples 20 minutes apart in the same person can differ substantially — which is why the interpretable ACTH is one drawn at the same moment as a cortisol, not one drawn on its own.
- Cortisol feedback. Exogenous glucocorticoids — oral, injected, inhaled or topical in sufficient dose — suppress ACTH, and that suppression is the commonest reason a person has a low one.
- Acute physical or psychological stress, which drives CRH and raises ACTH within minutes, including the stress of a difficult cannulation.
- Adrenal failure, which removes the feedback and drives ACTH high; and a corticotroph adenoma or an ectopic source, which drives it high while cortisol is also high Flowers 2023.
- Sleep phase and shift work, which move the whole curve rather than the amplitude, so an apparently abnormal morning value can be a correctly timed sample in the wrong body clock.
What changes only the reading:
- Sample handling. The dominant analytical term for this marker. Warm plasma, delayed separation or the wrong tube degrades the peptide and lowers the result Caruso 2020.
- Which assay. Demonstrated directly: 113.0 pg/mL on one platform, normal on another, same patient Yang 2022.
- Heterophile and anti-reagent antibodies, which in a sandwich format raise the result Ghazal 2022.
- Biotin on streptavidin platforms, which in a sandwich assay usually lowers it Balzer 2023.
- Cross-reacting precursors from an ectopic source, which some epitope pairs count and others do not Haddad 2019.
Reference interval or decision threshold — which kind of number ACTH (Adrenocorticotropic Hormone) is
A reference interval, and one that is only valid for the hour it was built in. The commonly quoted 7.2–63 pg/mL is a morning interval — the central 95% of a population sampled near the peak of the circadian curve, on one platform, with no outcome attached.
Two laboratories disagree for reasons that are all specific to this peptide: different epitope pairs counting different amounts of precursor Haddad 2019, different draw times behind the reference population, and different degrees of preanalytical degradation across the collection network Caruso 2020.
ACTH has no decision threshold of its own, and this is the single most important sentence on the page. It is a LOCALIZING test, and the unit of interpretation is the PAIR: ACTH read against a cortisol drawn from the same needle at the same minute. High cortisol with high or normal ACTH points at the pituitary or an ectopic source; high cortisol with suppressed ACTH points at the adrenal; low cortisol with high ACTH is primary adrenal failure; low with low is pituitary or exogenous steroid. An ACTH number alone answers none of those questions.
Where real thresholds exist in this axis they belong to dynamic tests — the cortisol response to synthetic ACTH, dexamethasone suppression, late-night salivary cortisol — and the laboratory review of Cushing syndrome exists largely to explain how those thresholds are undermined by cortisol-binding globulin, by cross-reacting metabolites and by the choice of specimen Flowers 2023.
How you would know your ACTH (Adrenocorticotropic Hormone) was wrong — and when to redraw
The window is set by the circadian curve, not by an interval in weeks. If the value does not fit the clinical picture, the correct repeat is a properly collected 7–9am draw with a simultaneous cortisol, into a chilled EDTA tube that reaches the centrifuge cold Caruso 2020. Nothing about waiting three months improves an ACTH; correct collection does.
What would have to change for the second value to mean anything:
- Cortisol, drawn at the same moment, in the direction that makes physiological sense. ACTH moving while cortisol sits still is the signature of an assay or handling problem rather than a corticotroph.
- DHEA-S, which is ACTH-dependent and slow-moving, so it carries a memory of adrenal drive that a single ACTH cannot. Chronically high ACTH with a persistently low DHEA-S needs explaining.
- CMP for sodium and potassium, since primary adrenal insufficiency classically brings hyponatremia and hyperkalemia with it, and their absence weakens the case.
- TSH and free T4, because a pituitary problem rarely confines itself to one axis.
The falsifying rule is the one the published case report reached: when the assay and the clinical criteria disagree, the assay is the thing to re-examine — on a second platform if necessary, because a value normal on one analyzer and markedly abnormal on another has been documented Yang 2022 Alvarez-Payares 2021.
What ACTH (Adrenocorticotropic Hormone) cannot tell you
It cannot be interpreted alone. Not ‘is best interpreted with cortisol’ — cannot. Every one of the four diagnoses this test participates in is defined by an ACTH-cortisol combination, and the same ACTH value appears in opposite diagnoses depending on the cortisol beside it.
It cannot localize a source within the ACTH-dependent group. Separating a pituitary adenoma from an ectopic secretor needs dynamic testing, imaging and often inferior petrosal sinus sampling; the peripheral number does not do it Flowers 2023.
It cannot be trusted if the tube was warm. Degradation is silent, it moves the result downward, and nothing on the report tells you it happened Caruso 2020.
It cannot be compared with a result from another laboratory. Different epitope pairs count different amounts of precursor Haddad 2019, and a documented case moved from 113.0 pg/mL to normal on a change of platform alone Yang 2022.
It cannot measure ‘adrenal fatigue’, and a mid-range morning ACTH does not exclude adrenal insufficiency — that is what the stimulation test is for.
The wrong inference readers draw is that a low ACTH means the adrenals are underdriven and the person needs support. The commonest real explanation for a suppressed ACTH is exogenous glucocorticoid, including inhaled and topical routes; the second is a badly handled specimen. Neither is treated with a supplement, and a suspected adrenal insufficiency is an urgent endocrine referral rather than a protocol.
Sources read for these sections
- Yang YY, et al. A Pitfall of Falsely Elevated ACTH: A Case Report and Literature Review. Journal of Investigative Medicine High Impact Case Reports 2022 · PMID 35699218
- Flowers KC, et al. Pitfalls in the Diagnosis and Management of Hypercortisolism (Cushing Syndrome) in Humans; A Review of the Laboratory Medicine Perspective. Diagnostics (Basel) 2023 · PMID 37189516
- Alvarez-Payares JC, et al. Common Pitfalls in the Interpretation of Endocrine Tests. Frontiers in Endocrinology 2021 · PMID 34557164
- Caruso B, et al. Causes of Preanalytical Interferences on Laboratory Immunoassays - A Critical Review. EJIFCC 2020 · PMID 32256291
- Haddad RA, et al. Interpretation of common endocrine laboratory tests: technical pitfalls, their mechanisms and practical considerations. Clinical Diabetes and Endocrinology 2019 · PMID 31367466
- Ghazal K, et al. Hormone Immunoassay Interference: A 2021 Update. Annals of Laboratory Medicine 2022 · PMID 34374345
Where to start with ACTH (Adrenocorticotropic Hormone)
In this order. Start at the supplement and you learn nothing, because you never established the number was real.
You have the range, where it came from and the first two moves. Inside is the rest of the five-pathway protocol — supplements, hormones, peptides — the order to run them in, and what to change when the number will not move.
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What people use ACTH (Adrenocorticotropic Hormone) to decide
Nobody orders a test for its own sake. ACTH (Adrenocorticotropic Hormone) is on the test list for these pathways — each one links to what the pathway claims, and what its test list is read for before you spend anything on it.
A four-point salivary cortisol curve is worth far more than a single morning serum draw — the pattern is the diagnosis. Low morning and high evening is the wired-and-tired picture, and it responds to adaptogens rather than to stimulants.
The rhythm is the diagnosis, not the level. Worth being blunt: 'adrenal fatigue' is not a recognized condition and the glands rarely fail — but a flattened cortisol curve is real, measurable and treatable.
What moves your ACTH (Adrenocorticotropic Hormone)
1 supplement in the Vault have a documented effect on this marker, or are a reason to have measured it first:
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Why your ACTH (Adrenocorticotropic Hormone) might be wrong
Most abnormal results are interference, not disease. Check these before you change anything. Each says whether the number is wrong (repeat it), badly timed (redraw it), or real with a cause.
ACTH degrades rapidly at room temperature. It must go into a chilled EDTA tube, on ice, and be separated quickly. A mishandled sample reads falsely low, which is the direction that changes a diagnosis.
Confirm the lab's handling before drawing. A surprisingly low ACTH is worth repeating with attention to transport.
Follows a daily rhythm with a morning peak, so a value drawn at 8am and one drawn at 2pm are not comparable numbers.
Draw between 7 and 9am, and use the same window every time you retest.
Suppress ACTH through negative feedback — including inhaled, nasal and topical preparations that people do not think of as steroids.
Declare every steroid route before an adrenal workup.
What ACTH (Adrenocorticotropic Hormone) means in combination
One marker tells you a little; combinations tell you the story. These are the named patterns this one takes part in.
The single most important pairing in adrenal medicine and the reason cortisol alone is close to useless. High ACTH with low cortisol means the gland is failing and the pituitary is compensating — primary adrenal insufficiency. Low or inappropriately normal ACTH means the signal never arrived, which is a pituitary problem with a different workup entirely.
Either way this is a doctor, promptly — untreated adrenal insufficiency can kill in a crisis. Check sodium and potassium on the same CMP: low sodium with high potassium supports the primary pattern.
What a proper workup looks like
This one’s retest schedule belongs with a clinician, not a calendar — so the useful thing to know is what a good assessment looks like, enough to tell whether you got one.
Low cortisol with a HIGH ACTH is primary adrenal insufficiency, and an untreated adrenal crisis can kill within hours. If you have that pattern alongside vomiting, dizziness on standing, salt craving or unexplained weight loss, that is an appointment today — not a retest, and not something to work around. Everything below assumes you are well enough to plan.
A paired 8am cortisol and ACTH from the same draw. Neither number means much without the other, and labs routinely run one without the other unless you ask. If cortisol is low, the next test is a short cosyntropin (Synacthen) stimulation test — 250 mcg, with cortisol measured at baseline, 30 and 60 minutes. Where primary adrenal insufficiency is suspected, 21-hydroxylase antibodies identify the autoimmune cause and renin with aldosterone shows whether the mineralocorticoid arm is affected too.
ACTH is one of the most fragile analytes in the lab, and this is where it usually goes wrong. It needs a chilled EDTA (lavender) tube, on ice, spun and separated quickly. Left at room temperature it degrades, and a degraded sample reads falsely LOW — which flips the interpretation from your adrenals are not responding to your pituitary is not signaling. Those are two different diagnoses with two different treatments. Timing is not optional either. Cortisol and ACTH follow a daily rhythm and peak in the early morning; an afternoon draw can make a healthy person look deficient.
High ACTH + low cortisol → primary (Addison's): the gland has failed and the pituitary is shouting. Low or inappropriately normal ACTH + low cortisol → secondary, a pituitary problem, most commonly suppression from long-term steroid use. Inappropriately normal is the subtle one — a mid-range ACTH is the wrong answer when cortisol is on the floor.
If your stimulation test was called abnormal, ask which assay was used. The classic cutoff is a peak cortisol of 18 µg/dL (500 nmol/L), and that number comes from older assays. Modern specific assays (Roche Elecsys II, Beckman Access, LC-MS/MS) read lower, and the current recommendation is roughly 14–15 µg/dL depending on the assay. Applying the old 18 to a modern assay produces about twice as many adrenal insufficiency diagnoses as it should — people started on lifelong steroids who did not need them.
“Which cortisol assay did you use, and what peak cutoff are you applying?”
J Endocr Soc 2021;5(4):bvab022 — new cortisol cutoffs after ACTH stimulation
What to test next
These put ACTH (Adrenocorticotropic Hormone) in context — each with its own full breakdown.
Frequently asked questions
7.2–63 pg/mL (morning). Ranges vary by laboratory and assay — always compare to the range printed on your own report.
Within range on a properly timed morning draw. No guideline body publishes an optimal ACTH concentration; adrenal guidance uses ACTH paired with a simultaneous cortisol.
With low cortisol, suggests the adrenals aren't responding — a serious diagnosis requiring prompt evaluation.
With low cortisol, suggests pituitary dysfunction or suppression from long-term steroid use — including from prolonged high-dose corticosteroid or, occasionally, heavy AAS use affecting the HPA axis.
You can order ACTH (Adrenocorticotropic Hormone) directly through Marek Diagnostics without a doctor's visit — drawn at any Quest Diagnostics location in the US. Code CAMERON applies 10% off automatically.
Where this goes next
This page is the free framework. The protocol itself — the dosing, the order to correct things in, the week-by-week schedule and what to retest — is a lesson inside Skool.