ACTH Test · Blood

If your cortisol is off, the next question is always: why? ACTH (adrenocorticotropic hormone) answers that question. It is the command signal your pituitary gland sends to your adrenal glands, telling them how much cortisol to make. A cortisol test alone tells you the output. ACTH tells you what is driving that output, and whether the problem is in your brain, your adrenal glands, or something else entirely.

That distinction matters because the same cortisol reading can mean completely different things depending on what ACTH is doing. High cortisol with high ACTH points toward a pituitary tumor or an ectopic hormone source. High cortisol with low ACTH points toward an adrenal problem. Low cortisol with high ACTH means the adrenals are failing. Low cortisol with low ACTH means the pituitary itself has gone quiet. Without ACTH, you are guessing.

How ACTH Controls Your Cortisol

ACTH is a 39-amino-acid peptide, meaning it is a small protein chain. It is made by specialized cells called corticotrophs in the front part of your pituitary gland, a pea-sized organ at the base of your brain. These cells chop ACTH out of a larger precursor protein called POMC (proopiomelanocortin). When your brain senses stress, low blood sugar, inflammation, or simply that it is early morning, a region of the brain called the hypothalamus releases CRH (corticotropin-releasing hormone), which tells the pituitary to release ACTH into your bloodstream.

ACTH travels to your adrenal glands, which sit on top of your kidneys, and stimulates them to produce cortisol and, to a lesser extent, adrenal androgens (weak male hormones that both men and women have). Once cortisol rises high enough, it feeds back to the pituitary and hypothalamus, telling them to reduce ACTH. This feedback loop is called the HPA (hypothalamic-pituitary-adrenal) axis, and it is the central control system for your body's stress response.

ACTH is released in bursts, not as a steady stream. It follows a strong daily rhythm: levels peak between about 4 AM and 8 AM and drop to their lowest point late in the evening. Changes in how big these bursts are (their amplitude) matter more than how often they happen when your body adapts to different levels of stress.

Cushing's Syndrome: When ACTH Drives Too Much Cortisol

When a pituitary tumor (usually a small, noncancerous growth called a corticotroph adenoma) makes too much ACTH, the result is Cushing's disease. Your adrenals respond to the relentless ACTH signal by overproducing cortisol. Over months to years, this causes central weight gain, a round face, thinning skin, easy bruising, high blood sugar, high blood pressure, weak muscles, fragile bones, and a significantly higher risk of infections and cardiovascular events.

ACTH can also come from tumors outside the pituitary, a condition called ectopic ACTH syndrome. Hormone-producing tumors (called neuroendocrine tumors) in the lungs, the thymus (a gland behind the breastbone), the pancreas, and even adrenal tumors called pheochromocytomas can secrete ACTH or CRH, causing severe and rapid-onset cortisol excess with profound muscle weakness, dangerously low potassium, severe high blood pressure, and weight loss. This pattern is often overlooked initially because the symptoms can mimic other conditions.

Distinguishing pituitary from ectopic ACTH sources is one of the hardest problems in endocrinology. A meta-analysis of dynamic testing found that measuring ACTH changes after a CRH injection had a pooled sensitivity of about 87% and specificity of about 94% for identifying pituitary Cushing's versus ectopic sources. When imaging and noninvasive tests are inconclusive, an invasive procedure called bilateral inferior petrosal sinus sampling (BIPSS), where blood is drawn from veins draining the pituitary, remains the gold standard.

Adrenal Insufficiency: When the Signal or the Response Breaks Down

In primary adrenal insufficiency (Addison's disease), the adrenal glands themselves are damaged, usually by an autoimmune attack. Cortisol production drops. Without the usual cortisol feedback to slow it down, the pituitary ramps up ACTH, sometimes to extreme levels. The Endocrine Society guideline notes that a morning ACTH above twice the upper limit of your lab's reference range, combined with low cortisol, strongly supports primary adrenal insufficiency. Values above 300 pg/mL with cortisol below 5 µg/dL are considered diagnostic.

In secondary adrenal insufficiency, the problem is upstream: the pituitary itself is not making enough ACTH. This can happen after pituitary surgery, radiation, a pituitary tumor compressing healthy tissue, or most commonly after long-term use of oral steroids (prednisone, dexamethasone) that suppress the pituitary's ACTH-producing cells. In these cases, both ACTH and cortisol are low. Without treatment, this can lead to fatigue, low blood pressure, low blood sugar, salt imbalances, and in severe cases, a life-threatening adrenal crisis.

A subtler pattern can appear early in primary adrenal insufficiency: ACTH begins to rise while cortisol is still in the normal range. The pituitary is working harder to maintain normal cortisol output from damaged adrenals. This is an early warning sign that standard cortisol-only testing may miss entirely.

ACTH in Critical Illness and Infection

During severe illness like sepsis, something unexpected happens: cortisol often climbs to very high levels while ACTH stays inappropriately normal or even low. This "ACTH-cortisol dissociation" appears to result from a combination of factors. Increased levels of the ACTH precursor protein POMC circulate without being properly processed into active ACTH, and inflammatory signals stimulate the adrenals through non-ACTH pathways. The adrenals themselves can also become less responsive to whatever ACTH is present.

A similar pattern was observed in some COVID-19 patients, where both ACTH and cortisol were inappropriately low for the severity of illness, suggesting the virus may directly impair HPA axis function. In one study of 28 hospitalized COVID-19 patients, cortisol and ACTH levels were lower than expected, pointing to impaired stress hormone production during active infection.

The practical takeaway: an ACTH value drawn during critical illness, sepsis, or severe infection does not reflect your normal pituitary function. Any testing for adrenal or pituitary disease should be deferred until you have fully recovered, unless there is immediate clinical need.

ACTH, Depression, and Chronic Stress

The HPA axis is central to the biology of depression. In melancholic depression (the subtype marked by severe low mood, insomnia, loss of appetite, and inability to feel pleasure), the HPA axis tends to be overactive, with higher baseline cortisol and exaggerated ACTH responses to stress. In atypical depression (marked by oversleeping, increased appetite, and heaviness in the limbs), HPA axis function is often normal or even blunted.

Childhood trauma also reshapes the ACTH stress response in lasting ways. In a landmark study of 49 women, those who had experienced childhood abuse showed dramatically amplified ACTH and cortisol responses to a standardized stress test, with the greatest increases in women who also had current depression. A separate study in 50 healthy adults with no psychiatric diagnosis found that a history of childhood maltreatment was associated with blunted ACTH and cortisol responses. The direction of the change appears to depend on whether the person has developed a psychiatric condition.

Reference Ranges

ACTH reference ranges depend heavily on when the blood is drawn and which assay your lab uses. A multicenter study testing the same plasma samples across 35 laboratories using seven different assays found that some assays achieved less than 10% variability, while others exceeded 20%. Near the clinically important threshold of 20 pg/mL, the all-laboratory coefficient of variation (a measure of how much results scatter around the true value) ranged from 29% to 33%. A separate comparison of two widely used assays (Roche and Siemens) found that 9.3% of samples showed a greater than 50% difference in ACTH results between the two platforms.

These ranges come from manufacturer specifications and validation studies using morning blood draws in healthy adults. Because of the large variability between assays, always compare your results within the same lab over time rather than against a fixed universal number.

A note below the table: these values are orientation ranges, not rigid cutoffs. Your lab may report slightly different numbers. What matters most is the pattern, specifically whether ACTH is high, normal, or low relative to your cortisol, and whether that pattern changes over time.

When Results Can Be Misleading

ACTH is one of the most challenging hormones to measure accurately. The biggest source of error is assay-to-assay variability: a multicenter quality-control study found that only 60% of measurements from patients with truly suppressed ACTH were correctly classified as low, meaning about 4 in 10 suppressed values were reported as normal. Assays correctly identified normal and high ACTH about 90% and 95% of the time, respectively.

• Time of day: ACTH can be three to five times higher at 6 AM than at 10 PM. A morning draw is essential for any meaningful interpretation. Blood drawn in the afternoon or evening will produce a much lower number that could falsely suggest pituitary suppression.
• Glucocorticoid use: Prednisone, dexamethasone, and other corticosteroids suppress ACTH production. If you are currently on steroids or have recently stopped them, your ACTH will be low as a drug effect, not because of pituitary disease. After stopping steroids, ACTH can temporarily spike during HPA axis recovery before normalizing.
• Acute stress and exercise: Intense physical activity, painful procedures, or acute psychological stress in the hours before your blood draw can transiently raise ACTH. Aim for a calm, rested morning draw.
• Critical illness, surgery, or infection: Major illness dramatically alters ACTH-cortisol relationships through inflammatory mediators and altered cortisol metabolism. Do not use ACTH results drawn during hospitalization to assess baseline pituitary function.

ACTH is also physically fragile in the blood sample. It degrades quickly at room temperature. The sample must be collected in a pre-chilled EDTA tube (a purple-top tube kept on ice), transported on ice, and processed rapidly. If your lab does not follow cold-chain handling, the result may be falsely low.

Tracking Your Trend

Because of the high variability between assays and the strong influence of time-of-day, stress, and sample handling, a single ACTH value is rarely enough to make a clinical decision. The most reliable approach is to test ACTH alongside cortisol at the same time of day (ideally between 7 and 9 AM), at the same lab, under the same conditions, and compare values over time.

If you are investigating a possible adrenal or pituitary problem, expect to need at least two consistent readings before acting. If you are monitoring recovery after stopping long-term steroids, test every 3 to 6 months until the axis recovers. If you are on immune checkpoint inhibitors for cancer, serial ACTH monitoring can detect pituitary inflammation (hypophysitis) before adrenal insufficiency develops, as ACTH may transiently rise before crashing.

For people tracking ACTH as part of broader stress-axis monitoring, an annual morning draw alongside cortisol gives you a meaningful baseline. If you are making lifestyle changes aimed at managing chronic stress, retesting in 3 to 6 months can reveal whether the HPA axis is shifting.

What to Do With an Abnormal Result

An abnormal ACTH result should always be interpreted alongside a simultaneous morning cortisol. The combination of the two values is far more informative than either one alone. If both are abnormal, the next steps depend on the pattern.

• High ACTH, low cortisol: This pattern suggests primary adrenal insufficiency. Retest to confirm, then see an endocrinologist. A cosyntropin stimulation test (also called an ACTH stimulation test, where synthetic ACTH is injected and cortisol response is measured) is the standard next step to confirm the diagnosis. Additional testing for adrenal antibodies and electrolytes (sodium, potassium) should follow.
• Low ACTH, low cortisol: This suggests secondary adrenal insufficiency from a pituitary or hypothalamic problem. An MRI of the pituitary and evaluation of other pituitary hormones (thyroid, growth hormone, sex hormones) are the next steps. Review your medication history carefully, as prior steroid use is the most common cause.
• High ACTH, high cortisol: This raises concern for Cushing's disease or ectopic ACTH production. First-line screening includes 24-hour urine free cortisol, late-night salivary cortisol, and the 1 mg dexamethasone suppression test. If confirmed, dynamic testing (CRH stimulation) and pituitary MRI help localize the source. An endocrinologist with experience in Cushing's syndrome should guide this workup.
• Low ACTH, high cortisol: This points toward an adrenal tumor producing cortisol independently (ACTH-independent Cushing's) or, during acute illness, toward the normal critical-illness pattern of ACTH-cortisol dissociation. If you are not acutely ill, an adrenal CT scan is the next step.

If your ACTH is borderline or your result does not match your symptoms, the most productive next step is to retest under ideal conditions: a calm morning draw at 7 to 9 AM, fasted, at the same lab, with cold-chain sample handling confirmed. If the pattern persists, involve an endocrinologist.