ACTH Blood Test: How to Read Adrenocorticotropic Hormone (ACTH) With Cortisol

Understand ACTH results alongside cortisol.

Published

September 30, 2026

Read time

7 min read

Medically reviewed by

Rhonda Collins, FNP-C

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What is an ACTH blood test?

An ACTH blood test measures adrenocorticotropic hormone, also called corticotropin, in a plasma sample. The pituitary gland at the base of the brain makes ACTH. ACTH tells the adrenal glands, which sit above the kidneys, to make cortisol. MedlinePlus explains the ACTH test.

What does ACTH do?

ACTH is the middle step in a feedback loop. The hypothalamus signals the pituitary, the pituitary releases ACTH, and ACTH drives the adrenal glands to release cortisol. Rising cortisol then signals the hypothalamus and pituitary to make less ACTH. When cortisol drops, ACTH normally rises. MedlinePlus describes this feedback system.

ACTH follows a daily rhythm. It is highest in the morning and lowest in the evening, and it is released in pulses, so the collection time is part of the result. Labcorp’s ACTH test reference notes both points.

Why is ACTH tested with cortisol?

ACTH on its own rarely answers a question. Its value is in showing where a cortisol problem starts: in the adrenal glands, in the pituitary, or in a tumor elsewhere that makes ACTH. MedlinePlus notes that the ACTH level is usually compared with the cortisol level, and that other tests are often needed for a final diagnosis. MedlinePlus explains why the two are read together.

Is ACTH a general screening test?

No. An ACTH test is usually ordered after an abnormal cortisol result, or when someone has symptoms of too much or too little cortisol. MedlinePlus lists these reasons.

When cortisol excess is suspected, the Endocrine Society recommends starting with a cortisol test such as a urine cortisol, late-night saliva cortisol, or dexamethasone suppression test. ACTH testing comes after abnormal results are confirmed, to look for the cause. Endocrine Society guideline on Cushing’s syndrome, 2008. When low cortisol is suspected and a stimulation test is not possible first, the Endocrine Society suggests measuring morning ACTH and cortisol together as an initial step. Endocrine Society guideline on primary adrenal insufficiency, 2016.

If you want to check cortisol itself, start with our guide on how to test cortisol levels, which compares blood, saliva, and urine options.

How does the ACTH blood draw work?

ACTH is a demanding sample, so the timing and handling matter more than for most blood tests.

• Morning timing. Labcorp asks for ACTH to be drawn between 7 a.m. and 10 a.m., and its reference range applies to samples collected in that window. Book an early appointment.
• Cold handling. The blood goes into a chilled lavender-top (EDTA) tube, is centrifuged immediately after collection, and the plasma is frozen until testing. Labcorp rejects a sample that has thawed.
• Tube type. ACTH sticks to untreated glass, so a sample collected in the wrong tube can read falsely low.
• Biotin. High-dose biotin supplements can interfere with the assay, so mention them when you order.

Labcorp lists these collection requirements. Your provider may ask you to fast for several hours first. MedlinePlus covers preparation.

Does steroid medicine affect an ACTH test?

Yes, it can. Glucocorticoid medicines such as prednisone act like cortisol. Long-term, high-dose use can cause Cushing’s syndrome and lower ACTH. Stopping them after long-term use can lead to adrenal insufficiency. NIDDK describes glucocorticoid-related Cushing’s syndrome; NIDDK describes adrenal insufficiency after stopping glucocorticoids. The Endocrine Society recommends ruling out glucocorticoid use before testing for Cushing’s syndrome. Endocrine Society guideline, 2008. List every medicine, cream, inhaler, and steroid injection you use, including joint injections, and do not stop a prescribed steroid for the test unless your provider tells you to. MedlinePlus advises against stopping medicines on your own.

What can high or low ACTH with cortisol suggest?

These patterns point a clinician toward possible explanations. They are not diagnoses, and confirming any of them takes further testing. “High” and “low” refer to the reporting laboratory’s reference ranges for the time of collection.

MedlinePlus describes all four patterns; Labcorp lists ectopic ACTH sources; NIDDK explains primary, secondary, and tertiary adrenal insufficiency.

The last row shows why the pairing matters. An ACTH value inside its reference range can still be too low for the situation when cortisol is low, because ACTH would normally rise.

What ACTH level is concerning?

There is no single ACTH number that is concerning for everyone. Use the reference range, units, and collection time printed on your own lab report. Labcorp’s ACTH range, for example, applies only to samples collected between 7 a.m. and 10 a.m. Labcorp shows its time-specific range. What makes a result concerning is usually the pattern with cortisol and your symptoms, not the ACTH value alone. For cortisol ranges, see our normal cortisol levels guide.

What are the symptoms of high or low ACTH?

ACTH itself causes few symptoms. Most symptoms come from the cortisol problem behind it.

When ACTH and cortisol are both high, symptoms of too much cortisol may include weight gain, thin arms and legs, a round face, extra fat at the base of the neck or between the shoulders, easy bruising, wide purple streaks on the skin, and muscle weakness. MedlinePlus lists these signs.

When ACTH is high and cortisol is low, as in Addison’s disease, the symptoms are those of too little cortisol. NIDDK also notes darkening of the skin in Addison’s disease, most visible on scars, skin folds, knuckles, and lips. NIDDK describes adrenal insufficiency symptoms.

When ACTH is low and cortisol is low, symptoms of too little cortisol include long-lasting fatigue, muscle weakness, loss of appetite, weight loss, and abdominal pain. If a pituitary tumor is the cause, headaches and vision problems can also occur. MedlinePlus describes low cortisol and pituitary symptoms.

Sudden severe pain in the lower back, abdomen, or legs with vomiting, diarrhea, weakness, or confusion can signal adrenal crisis, which NIDDK describes as an emergency. NIDDK explains adrenal crisis.

What tests follow an abnormal ACTH result?

A clinician chooses follow-up tests from the pattern. Common ones include:

• ACTH stimulation test. Cortisol is measured before and after an injection of synthetic ACTH, to see whether the adrenal glands respond. It is the test most often used to diagnose adrenal insufficiency.
• Dexamethasone suppression test. Cortisol is measured after a dose of dexamethasone, a glucocorticoid. Cortisol normally drops afterward, so a level that stays high suggests cortisol excess.
• Imaging and other hormone tests, such as a pituitary MRI or a CRH stimulation test, to find the source.

Each of these is ordered, timed, and interpreted by a clinician. NIDDK describes adrenal insufficiency testing; NIDDK describes Cushing’s syndrome testing.

When should I see an endocrinologist?

The Endocrine Society recommends that people with an abnormal screening result for Cushing’s syndrome see an endocrinologist for confirmation and further testing. Endocrine Society guideline, 2008. An abnormal ACTH result paired with a high or low cortisol result, or symptoms like those above, is a reason to take your lab report, collection time, and medicine list to an endocrinologist.

ACTH testing with Mito

The Adrenocorticotropic Hormone (ACTH) Blood Test measures plasma ACTH. Its result is most useful next to a cortisol result from the same morning, so read it with our cortisol biomarker page. Check the product page for current pricing and availability.

Photo by Hamish Duncan on Unsplash.