An ACTH blood test measures adrenocorticotropic hormone, the pituitary signal that tells your adrenal glands how much cortisol to make. Doctors rarely order it on its own. It usually appears on a lab slip alongside cortisol, because the two numbers only make sense when you read them together: cortisol tells you how much stress hormone is circulating, while ACTH tells you where the instruction came from. That pairing is what turns a confusing result into a usable answer about whether a problem sits in the pituitary gland, the adrenal glands, or somewhere else entirely. In this article you will learn what the test measures, why the blood draw is scheduled so early in the morning, how to read your number against the reference range, what high and low results typically point to, and which everyday factors can distort the result.
What an ACTH blood test measures
Adrenocorticotropic hormone is a small protein released by the anterior pituitary, a pea-sized gland sitting just beneath the brain. Its job is narrow and specific: it travels through the bloodstream to the outer layer of the adrenal glands, which sit on top of each kidney, and instructs them to produce cortisol. Cortisol in turn helps regulate blood sugar, blood pressure, inflammation, and the body’s response to physical and emotional stress.
The laboratory reports ACTH in picograms per milliliter (pg/mL), or in picomoles per liter (pmol/L) in some labs. The value is a snapshot of a single moment, which matters more here than for most markers, because ACTH is released in short bursts rather than as a steady stream. Two draws taken twenty minutes apart in the same healthy person can differ noticeably, and that variability is normal rather than a laboratory error.
Because ACTH exists only to drive cortisol production, the test almost never travels alone. Most clinicians pair it with a morning cortisol blood test result drawn from the same sample, and sometimes with a 24-hour collection measuring cortisol excreted in the urine over a full day.
How ACTH and cortisol control each other
The system works like a household thermostat. The hypothalamus, a control center in the brain, releases corticotropin-releasing hormone. That prompts the pituitary to release ACTH. ACTH prompts the adrenal cortex to release cortisol. When enough cortisol is circulating, it signals back to both the hypothalamus and the pituitary to slow down. Endocrinologists call this arrangement the hypothalamic-pituitary-adrenal axis, and the feedback step is what keeps levels from spiraling in either direction.
This loop explains why the pairing of the two hormones is so informative. If cortisol is high and ACTH is also high, the pituitary is still pushing, which suggests the driver sits above the adrenal glands. If cortisol is high but ACTH is suppressed to near zero, the adrenal gland is producing cortisol on its own and the pituitary has correctly stopped signaling. The same logic runs in reverse for low cortisol.
Why the daily rhythm changes your number
ACTH follows a circadian rhythm, meaning it rises and falls on a roughly 24-hour cycle. Levels peak in the early morning, usually between 6 and 9 a.m., then fall through the day to their lowest point around midnight. A value that looks unremarkable at 8 a.m. could look strikingly low at 4 p.m. without anything being wrong. This is the single most common reason an ACTH result gets misread, and it is why the draw time is printed on the report.
Night shift workers, people with irregular sleep schedules, and travelers crossing time zones can have a rhythm shifted by several hours. Mentioning this to whoever orders the test lets them interpret the timing correctly rather than comparing your result to a reference range built for daytime sleepers.
Why doctors order an ACTH blood test
The test is a localizing tool. It is generally requested after another result or a cluster of symptoms has already raised a question about cortisol, not as part of a routine annual panel. Typical reasons include unexplained weight gain concentrated around the trunk and face, thinning skin that bruises easily, purple stretch marks, muscle weakness, persistent high blood pressure in a young adult, or the opposite picture of profound fatigue with weight loss, salt cravings, and low blood pressure.
It is also ordered to follow up on abnormal electrolytes. Adrenal problems frequently disturb the balance between sodium levels in the blood and potassium levels on a metabolic panel, and that pattern often prompts a wider hormonal workup that includes aldosterone and its effect on salt balance. Clinicians investigating broader pituitary function may add tests for other hormones the same gland produces, including prolactin and what its levels indicate and thyroid-stimulating hormone results.
A third use is monitoring. People already diagnosed with an adrenal or pituitary disorder may have ACTH rechecked periodically to see whether treatment is holding the axis in a reasonable range, or to detect a recurrence after pituitary surgery.
How the test is done and how to prepare
The draw itself is a standard venous blood sample from the arm, taking a couple of minutes. What differs from most blood tests is the handling. ACTH degrades quickly at room temperature, so the sample is collected in a chilled tube containing an anticoagulant, kept on ice, and spun down promptly. If a sample sits too long before processing, the reported value can fall below the true one. This is a laboratory concern rather than something you control, but it explains why ACTH is often drawn at a hospital lab rather than a walk-in collection site.
Preparation on your side is straightforward. Appointments are almost always scheduled in the early morning to catch the natural peak. Fasting is not usually required, though it may be if other tests such as a fasting glucose measurement are drawn from the same visit. Vigorous exercise, acute illness, and significant emotional stress in the hours before the draw can all raise ACTH, so a calm morning is worth arranging.
Medications matter more than food. Glucocorticoid drugs such as prednisone, hydrocortisone, and dexamethasone suppress ACTH directly, and that includes inhaled, topical, and injected forms that people often forget to mention. Estrogen-containing contraceptives, lithium, amphetamines, and some drugs used in critical care can also shift the result. Never stop a prescribed medication before a test on your own; tell the ordering clinician what you take and let them decide.
How to read your ACTH results
Reference ranges vary between laboratories because different assay platforms measure the hormone slightly differently. Always compare your number to the range printed on your own report rather than to a range found online. Two widely cited morning ranges give a sense of the scale.
| Source of the range | Morning reference range | Timing assumed |
|---|---|---|
| MedlinePlus, National Library of Medicine | 9 to 52 pg/mL (2 to 12 pmol/L) | Early morning draw |
| Cleveland Clinic | 7.2 to 63.3 pg/mL | Between 7 and 10 a.m. |
| Your own laboratory | Printed on the report, assay-specific | Draw time noted on the slip |
The overlap between those two ranges shows why a single borderline value is rarely conclusive. A result of 8 pg/mL sits just below one range and comfortably inside the other. What clinicians look for instead is the combination with cortisol.
Reading ACTH and cortisol as a pair
The table below shows the four basic patterns and what each one generally suggests. These are starting points for investigation, not diagnoses, and each pattern needs confirmation with further testing.
| ACTH | Cortisol | What the pattern usually points toward |
|---|---|---|
| High or normal | High | An ACTH-dependent cause, such as a pituitary tumor driving the axis or a hormone-producing tumor elsewhere in the body |
| Low or undetectable | High | An adrenal source of cortisol, or the effect of steroid medication taken from outside the body |
| High | Low | Primary adrenal insufficiency, where the adrenal glands cannot respond to a strong signal |
| Low or normal | Low | Secondary adrenal insufficiency, where the pituitary is not sending enough signal |
An out-of-range ACTH value on its own is not a diagnosis, and plenty of people discover an unexpected number while feeling perfectly well. If that describes you, this guide to abnormal results in someone without symptoms explains how clinicians weigh a lone outlier.
Conditions behind high and low ACTH
High ACTH with high cortisol most often reflects a benign pituitary tumor secreting excess hormone, the condition known as Cushing’s disease. Less commonly, a tumor outside the pituitary produces ACTH on its own; this is called ectopic secretion and is most often linked to certain lung and neuroendocrine tumors. Both sit under the broader umbrella of Cushing’s syndrome and its causes and treatments.
High ACTH with low cortisol points toward primary adrenal insufficiency, also called Addison’s disease. Here the adrenal glands are damaged, often by an autoimmune process, so the pituitary keeps raising the signal without effect. Symptoms build slowly and include fatigue, weight loss, low blood pressure, darkening of the skin at creases and scars, and cravings for salt. Adrenal androgens fall in the same setting, which is why a workup often includes DHEA-S and what the result reflects.
Low ACTH with low cortisol suggests the pituitary itself is underperforming, from a tumor, surgery, radiation, head injury, or inflammation. By far the most frequent cause, though, is long-term glucocorticoid treatment: sustained steroid use suppresses the pituitary, and the axis can take weeks or months to recover after the drug is tapered.
Low ACTH with high cortisol usually means the adrenal gland is generating cortisol independently, most often from an adrenal adenoma. It is also the expected picture in someone taking steroid medication, since the drug both raises measured cortisol activity and suppresses the pituitary signal.
What can distort a result, and when to see a doctor
Several ordinary factors move ACTH without any underlying disease. Acute stress, including the anxiety of the blood draw itself, raises it within minutes. Sleep deprivation and shift work displace the daily peak. Pregnancy raises levels through the later trimesters. Acute illness, surgery, and severe pain all activate the axis. Sample handling errors lower the measured value. None of these are reasons to dismiss an abnormal result, but they are reasons to repeat a borderline one under better conditions before drawing conclusions.
Contact a clinician promptly if an abnormal ACTH or cortisol result comes with severe weakness, dizziness on standing, vomiting, abdominal pain, confusion, or unexplained fever. That combination can signal an adrenal crisis, which is a medical emergency requiring immediate treatment. Book a non-urgent appointment if you notice gradual changes such as new central weight gain with thinning arms and legs, easy bruising, wide purple stretch marks, persistent muscle weakness, darkening skin, or fatigue that does not improve with rest. Bringing the actual report rather than a remembered number makes that conversation far more productive, and this walkthrough of reference ranges, flags, and next steps for lab results is a useful primer beforehand.
Latest scientific advances
Research over the past three years has focused less on the ACTH assay itself and more on how clinicians combine it with other results to reach an answer faster and with fewer invasive procedures. Here is what has changed, in plain terms.
A 2025 comprehensive review of Cushing syndrome, published in a leading review journal by a team including researchers at the National Institutes of Health, restated the central role of the ACTH measurement in sorting cases into two groups: those driven by ACTH and those that are not. What this means for you is that the test is not being replaced. It remains the fork in the road that decides whether imaging should focus on the pituitary gland or on the adrenal glands, which spares patients scans that were never going to be informative.
A 2024 study in a clinical endocrinology journal built personalized decision algorithms around urinary free cortisol, the amount of active cortisol spilling into a full day’s urine collection, in people whose excess cortisol was already known to be ACTH-driven. The researchers found that combining that urine measurement with routine clinical information could identify the likely source in many patients without going straight to an invasive sampling procedure. What this means for you is a realistic prospect of fewer catheter-based tests, though the approach still needs confirmation in other populations before it becomes standard practice.
A 2025 international retrospective study, meaning one that looked back at records already collected rather than following people forward, examined cyclic Cushing’s syndrome, an uncommon form in which cortisol excess switches on and off over weeks or months. It documented how frequently a single normal test in an off phase delays the diagnosis. What this means for you is straightforward: if your symptoms come and go, one normal ACTH or cortisol result does not close the question, and repeat testing during a symptomatic phase is reasonable to ask about.
A 2024 clinical review of ectopic Cushing’s syndrome, the form caused by an ACTH-producing tumor outside the pituitary, summarized how these cases present and why they are so often missed early. The practical takeaway is that a markedly high ACTH with severe, fast-moving symptoms tends to prompt a search beyond the pituitary, including chest imaging. A further 2025 review from an NIH-affiliated group set out the current diagnostic sequence for Cushing’s disease specifically, reinforcing that no single number confirms the diagnosis and that two independent abnormal tests are the usual threshold before proceeding.
Taken together, these are refinements rather than breakthroughs. The direction of travel is toward smarter sequencing of existing tests, which for patients generally means fewer procedures and a shorter path to an answer.
Glossary
| Term | Definition |
|---|---|
| Adrenocorticotropic hormone (ACTH) | A hormone made by the pituitary gland that tells the adrenal glands to produce cortisol. |
| Anterior pituitary | The front portion of the pituitary gland, the pea-sized structure below the brain that releases ACTH and several other hormones. |
| Adrenal cortex | The outer layer of each adrenal gland, where cortisol and related hormones are produced. |
| Cortisol | The main stress hormone, involved in blood sugar control, blood pressure, and inflammation. |
| HPA axis | Short for hypothalamic-pituitary-adrenal axis, the chain of signals linking the brain to the adrenal glands. |
| Negative feedback | The braking mechanism by which rising cortisol tells the brain and pituitary to slow ACTH release. |
| Circadian rhythm | The roughly 24-hour cycle that makes ACTH peak in the early morning and bottom out near midnight. |
| Ectopic secretion | Production of a hormone by tissue that does not normally make it, such as a lung tumor releasing ACTH. |
| Adrenal insufficiency | A state in which the adrenal glands do not make enough cortisol, either because they are damaged or because the pituitary signal is too weak. |
| Picogram per milliliter (pg/mL) | The unit used to report ACTH; a picogram is one trillionth of a gram. |
Frequently asked questions
Do I need to fast before an ACTH blood test?
Fasting is not usually required for an ACTH measurement on its own. The timing of the draw matters far more than food, which is why appointments are scheduled early in the morning. Some clinicians do ask for an overnight fast when other tests are collected from the same visit, or when a suppression test is planned. Follow the instructions on your lab slip, and if none were given, call the ordering office rather than guessing. Water is generally fine in all cases.
What is considered a low ACTH level?
That depends on the range your laboratory uses, since assay platforms differ. As an illustration, one widely used morning range starts at 9 pg/mL and another starts at about 7 pg/mL, so a value in single digits may be flagged by one lab and not another. Interpretation also depends entirely on the accompanying cortisol. A low ACTH alongside high cortisol has a very different meaning from a low ACTH alongside low cortisol, so the number is not judged in isolation.
Can I get an ACTH blood test done at home?
Home collection is generally not suitable for this marker. ACTH breaks down quickly once blood leaves the body, so the sample must be drawn into a chilled tube, kept on ice, and processed within a short window. Most direct-to-consumer kits cannot meet those handling requirements, and a mishandled sample tends to read falsely low. If you want the test, a laboratory draw arranged through a clinician is the reliable route, and it also ensures the result is interpreted alongside cortisol.
How long does it take to get ACTH results?
Turnaround is typically one to several business days, longer than a routine blood count because the sample is often sent to a specialized laboratory. Timing depends on where the sample is processed and whether cortisol or other hormones are being run alongside it. If your result is not available within a week, contacting the ordering office is reasonable. Ask that the report include the draw time, since interpretation depends on it.
Can stress temporarily raise my ACTH?
Yes. Physical and emotional stress activate the pathway within minutes, which is exactly what the hormone is designed to do. Acute illness, poor sleep, intense exercise, pain, and even anxiety about the needle can nudge a result upward. This is why a single mildly elevated value is often repeated under calmer conditions before anything is concluded. Persistent, substantial elevations accompanied by symptoms are what prompt a fuller investigation.
Why did my doctor order cortisol too?
Because ACTH on its own cannot tell you where a problem sits. The hormone’s whole purpose is to drive cortisol production, so the informative signal is the relationship between the two. Cortisol shows how much stress hormone is circulating; ACTH shows whether the pituitary is pushing hard, backing off, or behaving normally. Reading them together narrows the possibilities from a long list to one or two, and directs any imaging to the right gland.
Sources
- MedlinePlus, National Library of Medicine — ACTH blood test — MedlinePlus Medical Encyclopedia, updated 2025 — medlineplus.gov
- Cleveland Clinic — Adrenocorticotropic Hormone (ACTH): What It Is and Function — Cleveland Clinic Health Library, 2022 — my.clevelandclinic.org
- National Institute of Diabetes and Digestive and Kidney Diseases — Cushing’s Syndrome — NIDDK Health Information — niddk.nih.gov
- Mayo Clinic Staff — Addison’s Disease: Diagnosis and Treatment — Mayo Clinic Diseases and Conditions, 2024 — mayoclinic.org
- Nieman LK, Castinetti F, Newell-Price J, et al. — Cushing syndrome — Nature Reviews Disease Primers, 2025 — doi.org/10.1038/s41572-024-00588-w
- Elenius H, Nieman LK — Diagnosis of Cushing’s Disease — Endocrinology and Metabolism Clinics of North America, 2025 — doi.org/10.1016/j.ecl.2025.06.001
- Lavoillotte J, Mohammedi K, Salenave S, et al. — Personalized Noninvasive Diagnostic Algorithms Based on Urinary Free Cortisol in ACTH-dependent Cushing’s Syndrome — The Journal of Clinical Endocrinology and Metabolism, 2024 — doi.org/10.1210/clinem/dgae258
- Nowak E, Zhang Q, Zhang S, et al. — Cycle characterisation and clinical complications in patients with cyclic Cushing’s syndrome: insights from an international retrospective cohort study — The Lancet Diabetes and Endocrinology, 2025 — doi.org/10.1016/S2213-8587(25)00249-9
- Ragnarsson O, Juhlin CC, Torpy DJ, et al. — A clinical perspective on ectopic Cushing’s syndrome — Trends in Endocrinology and Metabolism, 2024 — doi.org/10.1016/j.tem.2023.12.003
Further reading
- Explore another pituitary signal measured on the same workup with this guide to luteinizing hormone levels and what they mean.
- Compare how a partner hormone from the same gland is interpreted by reading our follicle-stimulating hormone levels guide.
- Understand how growth signaling from the pituitary is assessed in this guide to IGF-1 blood test results.
- Check a marker that often shifts alongside long-term cortisol excess with our total calcium test results guide.
- Review a bone condition frequently linked to sustained high cortisol in this guide to osteoporosis symptoms, causes, and management.
Understand your lab results with BloodSense
An ACTH result only becomes meaningful next to the other numbers on your report, and that is exactly where most people get stuck. Values such as cortisol, sodium, potassium, and fasting glucose each carry a piece of the picture, and the pattern across them says more than any single figure. BloodSense translates a full lab report into plain language, showing where each marker sits against its reference range and how the results relate to one another, so you arrive at your appointment with clear questions rather than a page of unexplained numbers. It helps you understand your results; it does not diagnose, and it does not replace your doctor.
