ACTH blood test: what it measures, why it is ordered and how to prepare

An ACTH test measures adrenocorticotropic hormone in a sample of your blood. ACTH is made by the pituitary gland, a small gland at the base of the brain, and it tells your adrenal glands how much cortisol to make. So the test tells a clinician about the signal, and a cortisol test tells them about the response.

Many people land here after a cortisol result they don’t understand, or because a clinician mentioned ACTH. This page covers what the test is, why it is ordered, how the sample is handled and what to do before you have it.

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 the ACTH test measures

ACTH sits in the middle of a feedback loop. A part of the brain called the hypothalamus signals the pituitary gland. The pituitary releases ACTH. ACTH tells the adrenal glands, two small glands above your kidneys, to make cortisol. MedlinePlus says that when cortisol is low, ACTH normally rises, and when cortisol is high, ACTH normally falls. Our page on ACTH vs cortisol explains the loop.

The test measures how much ACTH is in your blood at the moment of the draw. Other names include ACTH blood test, ACTH plasma test and corticotropin.

Why a clinician orders it

MedlinePlus says an ACTH test helps diagnose and monitor conditions that affect cortisol levels, including disorders of the pituitary and adrenal glands. ACTH and cortisol tests are used together to help find out which type of condition may be behind an abnormal cortisol level. Other tests are often needed for a final diagnosis.

You may be sent for this test if you:

• had an abnormal result on a cortisol test, or
• have symptoms of too much cortisol, such as weight gain, a round face, easy bruising, wide purple streaks on the skin, or muscle weakness, or
• have symptoms of too little cortisol, such as long-lasting fatigue, muscle weakness, loss of appetite, weight loss or belly pain, or
• have symptoms of a pituitary problem, which can include headaches and vision changes.

Each of those symptoms has other common causes. Having one doesn’t mean your ACTH is off.

ACTH test or ACTH stimulation test

These are two different things, and people mix them up.

The ACTH blood test measures the hormone your body made. You have blood drawn and that is all.

The ACTH stimulation test is a clinic procedure. According to NIDDK, a health care professional gives an injection of man-made ACTH and takes blood before it and 30 or 60 minutes after, then measures cortisol in each sample. It is used most often to diagnose adrenal insufficiency. You can’t do it from home, and a clinician decides whether you need it.

How the test is done and how to prepare

A health care professional takes a blood sample from a vein in your arm. MedlinePlus says this usually takes less than five minutes, with a small sting and perhaps slight bruising afterward.

To prepare:

1. Follow your order’s instructions. MedlinePlus says you may need to fast for several hours, and that samples are often taken early in the morning when ACTH levels are at their highest for the day.
2. Tell your clinician every medicine you take. That includes steroid medicines, creams and supplements. Some medicines can affect results. Don’t stop any medicine unless your prescriber tells you to.
3. Mention biotin. A laboratory review says ACTH is usually measured with a type of immunoassay that can read falsely low in the presence of biotin. Ask your clinician or the lab whether to do anything about it. Don’t change a supplement on your own without asking.

Why the sample is handled with care

ACTH is present in very small amounts and doesn’t last long. A laboratory-medicine review gives its half-life in the body as about 6 to 7 minutes, and says specimens need careful handling. It states that samples for ACTH should be separated from the blood cells within 2 hours, and that hemolysis (damaged blood cells) or too much of the tube’s anticoagulant, EDTA, can give falsely low results.

What this means for you: you can’t control handling, but you can choose a lab that draws and processes plasma samples as part of its normal work, and follow its instructions. If the order doesn’t say how the sample is to be handled, ask the lab.

What the number looks like

ACTH is reported in picograms per milliliter (pg/mL), which equals nanograms per liter (ng/L). Your lab prints its own range beside the result. One medical-education review says ACTH peaks between 6 and 8 a.m. and is lowest around 11 p.m.

Treat that as one published range, not a cut-off. A laboratory review says there is no international standard or reference method for ACTH, so results from different assays can’t be compared directly. Use the range printed on your own report. For the daily pattern and why one number is hard to read, see ACTH levels.

What an ACTH test can’t show

• It can’t diagnose a condition by itself. MedlinePlus says your provider will usually compare ACTH with your cortisol level, and that abnormal results often need other tests to confirm the specific cause.
• It can’t be read without the time of day. ACTH changes through the day and with stress, so a sample time matters.
• It doesn’t explain how you feel. It measures a signal, and the symptoms people notice come from the cortisol level downstream or from the pituitary problem itself.
• It isn’t a test for “adrenal fatigue”. That isn’t a recognized diagnosis. See adrenal tests.

NIDDK says no one test is perfect for Cushing’s syndrome, and doctors usually do more than one. For adrenal insufficiency, NIDDK describes stimulation tests as the main route to a diagnosis.

What the seller’s page says

The seller’s ACTH page says the test measures ACTH levels in blood, and describes it as useful in telling primary from secondary adrenal disorders. It doesn’t state whether to fast, what time to have the blood drawn or how the sample should be handled. Where an order is silent, follow the instructions printed on your lab order and ask the lab if you aren’t sure. A banner on the seller’s site says most results come in one to three days.

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

When to see a clinician

An ACTH result is something to take to a clinician, along with your cortisol result and your medicines. If you take a steroid medicine, ask your prescriber how it affects ACTH testing and don’t stop it yourself.

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

Questions people ask

Do I have to fast for an ACTH test?

MedlinePlus says you may need to fast for several hours before the test. The seller’s page doesn’t state a rule, so follow the instructions on your lab order, or ask the lab.

Is the ACTH test the same as a cortisol test?

No. ACTH is the pituitary signal and cortisol is the adrenal hormone it triggers. Clinicians usually look at both. See AM and PM timing for the cortisol side.

Can I take an ACTH test at home?

MedlinePlus describes it as a blood sample taken from a vein by a health care professional. The seller’s page describes a blood test and doesn’t give collection details, so check how the sample is taken before you order.

Keep reading

• ACTH levels

  The daily rhythm, units and why one number is hard to read.

• ACTH vs cortisol

  How the two hormones work as a loop.

• Adrenal tests

  Every adrenal blood test and what it answers.

• Cortisol test guide

  Which cortisol test fits which question.