Low ACTH, high ACTH, normal ACTH: how ACTH levels work

A report that flags your ACTH as low or high is easy to over-read. This page explains how ACTH levels are set, why they move through the day, and why a lab can’t give one “normal” that fits every sample.

It doesn’t tell you what your own number means. That depends on things a web page can’t see: your cortisol at the same time, when the blood was drawn, what you take and your history. The clinician who ordered the test has those. If you want the basics of the test first, see the ACTH blood test page.

ACTH

One blood test for ACTH, the hormone that tells the adrenal glands to make cortisol.

$49

See this test at HealthLabs

Price checked November 2026. Not available in ND, RI, NY, NJ, MD and HI. We earn a commission on sales.

What sets your ACTH level

ACTH is made by the pituitary gland, and the brain’s hypothalamus tells the pituitary how much to make. ACTH then tells the adrenal glands to make cortisol. MedlinePlus says that when cortisol is low, ACTH normally rises, and when cortisol is high, ACTH normally falls, because the rising cortisol signals the hypothalamus to stop sending its message.

That feedback is why an ACTH level can’t be judged without a cortisol level beside it. The two are one system. Our page on ACTH vs cortisol walks through the loop.

Two other inputs matter:

• The body clock. A medical-education review says the hypothalamic signal (CRH) is released on a daily cycle, which sets the daily pattern of ACTH.
• Stress and low blood sugar. The same review says CRH may also be released in response to stress and hypoglycemia, which drives ACTH.

The daily rhythm

The same review says ACTH peaks between 6 and 8 a.m. and is lowest around 11 p.m. MedlinePlus says samples are often taken early in the morning because that is when ACTH is at its highest for the day.

ACTH also doesn’t last long once it is in the blood. A laboratory review gives its half-life as about 6 to 7 minutes. A reading is a snapshot of one moment, not a stable trait, which is one more reason the time of the draw matters.

Normal ACTH range: what is published and why it varies

Your lab prints its own range beside the result. Units of pg/mL and ng/L are the same. There is no single standard to hold a result against. Three reasons:

• Labs use their own ranges. The range on your report is the one for the method that ran your sample.
• There is no common standard. A laboratory review says there is no international standard or reference method for ACTH, so one assay’s number can’t be compared directly with another’s.
• Assays differ at the low end. The same review says an ACTH assay needs to report very low concentrations reliably, at least below 5 pg/mL, or true low values can’t be told apart. Not every method manages that.

Why “low ACTH” and “high ACTH” are never read alone

Low or high compared with what? A clinician asks at least three questions at once:

1. Compared with this lab’s range, for this time of day?
2. Compared with the cortisol drawn alongside it? MedlinePlus says your provider will usually compare your ACTH with your cortisol, and that abnormal results often lead to other tests to confirm the specific cause.
3. Compared with your own picture? That means your symptoms, your medicines, and what other tests show.

This is why this page won’t say “low ACTH means X”. The same ACTH figure can sit in very different situations depending on the answers above, and only a clinician with all of them can read it.

Things that can change the number

Before anyone reads much into one ACTH value, they check whether something about the sample or the day could have shifted it.

• Time of day. See the rhythm above.
• Sample handling. A laboratory review says ACTH specimens need careful handling, and that damaged blood cells or too much of the tube’s anticoagulant (EDTA) can distort results.
• Biotin. The laboratory review says ACTH assays of the common sandwich type can be affected by biotin. Tell your clinician if you take it.
• Stress and low blood sugar. Both can release the signal that drives ACTH, as above.
• Steroid medicines. Taking steroids for a long time acts on the same loop. NIDDK says high steroid levels over time cause the hypothalamus to make less CRH, and less CRH means less ACTH. That is one reason your prescriber needs to know before any ACTH test. Never stop or change a steroid yourself.

ACTH and symptoms

People search “low ACTH symptoms” and expect a list. ACTH itself has one main job, which is to signal the adrenal glands. MedlinePlus says a pituitary tumor can cause headaches and vision problems.

In other words, the symptoms people link to an ACTH result mostly come from cortisol being too low or too high, or from a pituitary problem. See low cortisol and high cortisol for the symptoms and how each is worked up. Those symptoms have many other causes, and none of them is proof of anything about ACTH.

If you have repeated vomiting, severe weakness or fainting, don’t wait for any test. Call 911 or go to the nearest emergency room. See adrenal crisis.

What to do with a flagged ACTH result

• Take the whole report to the clinician who ordered it. Bring the lab’s range, the time of the draw and any cortisol result from the same day.
• Tell them what you take. That includes steroids, creams, supplements and biotin.
• Ask what comes next. NIDDK describes follow-up tests in which a clinician gives a hormone and measures the response, such as the ACTH stimulation test, and imaging when a cause needs to be found. A clinician decides if any are needed.
• Don’t order repeat tests to chase a number. Two samples can differ for reasons a clinician has to sort out.

Prices for the same type of test vary widely between sellers, and it is worth comparing. See cost and where to buy.

Questions people ask

Does stress raise ACTH?

A medical-education review says CRH, the hypothalamic signal that drives ACTH, may be released in response to stress and low blood sugar. How much a given stress moves a given reading isn’t something one test can tell you.

Can one ACTH test tell me what is wrong?

No. MedlinePlus says ACTH is usually compared with cortisol and other tests are often needed. A single ACTH can’t diagnose a pituitary or adrenal condition.

Should I repeat the test?

That is a decision for the clinician who has your results. If the first draw had a handling problem or an odd time, they may ask for another.

Keep reading

• ACTH blood test

  What the test is, who gets it and how to prepare.

• ACTH vs cortisol

  How the two hormones work as a loop.

• Low cortisol

  Symptoms, emergency signs and how it is tested.

• Adrenal tests

  Every adrenal blood test and what it answers.