Low cortisol test: which tests are used and in what order

A low cortisol test usually means a blood cortisol drawn in the morning, often with an ACTH level, and then a stimulation test if the result isn’t clear. That is the order a clinician follows when adrenal insufficiency is suspected. No single step settles the question.

If you have repeated vomiting, fainting or weakness so severe you can’t do your usual activities, don’t read on and wait. Call 911 or go to the nearest emergency room. Suspected adrenal crisis is treated without waiting for test results. See low cortisol for the emergency signs. The rest of this page is about the testing itself.

Cortisol

One blood draw for one cortisol result. It can’t diagnose or rule out an adrenal condition by itself.

$109

Not for emergencies. If you have repeated vomiting, severe weakness or fainting, get urgent care instead of ordering a test. If you take a steroid medicine, ask your prescriber how it affects results.

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.

The tests for low cortisol, step by step

Step	Test	What it shows	Who arranges it
1	Morning serum cortisol	Cortisol when it is normally at its highest	A clinician, or you
2	ACTH, often drawn with the cortisol	Whether the pituitary is signalling the adrenal glands as expected	A clinician, or you
3	ACTH stimulation test	How much the adrenal glands respond to a dose of synthetic ACTH	A clinician
4	Insulin tolerance test or CRH stimulation test	Pituitary function, when earlier results are unclear	A clinician
5	Antibody tests, CT, MRI	The cause, once the diagnosis is made	A clinician

NIDDK says suspicion usually starts with your medical history and symptoms, and that early on adrenal insufficiency can be hard to diagnose because symptoms come on slowly. The next step it names is blood testing to see if cortisol is too low and to help find the cause.

Step 1: a morning cortisol

Cortisol peaks in the early morning and falls through the day, so the morning sample is the one that carries the most weight when the question is whether cortisol is too low. A low evening value is expected.

MedlinePlus says blood samples are often taken twice, in the morning and again around 4 p.m., and that this takes two appointments on the same day. The later sample shows how far the level falls. The morning sample is the one doctors lean on for adrenal insufficiency. The AM and PM timing page covers the practical side.

Step 2: ACTH

ACTH is the pituitary hormone that tells the adrenal glands how much cortisol to make. MedlinePlus says ACTH and cortisol tests are used together to help find out which type of condition may be behind abnormal cortisol levels. A review of primary adrenal insufficiency describes paired measurement of serum cortisol and plasma ACTH as the next step once it is suspected.

ACTH samples are often taken early in the morning, when ACTH is highest, and MedlinePlus says you may need to fast for several hours. The hormone breaks down quickly. A laboratory review says ACTH breaks down quickly, so samples must be spun and separated from the cells within 2 hours, and that broken blood cells or too much anticoagulant in the tube can give a falsely low result. So follow the lab’s instructions exactly. See the ACTH blood test page.

Step 3: the ACTH stimulation test

NIDDK calls this the test used most often to diagnose adrenal insufficiency. A health care professional gives an intravenous injection of man-made ACTH and takes blood before, and 30 or 60 minutes after. The normal response is a rise in cortisol. People with Addison’s disease show little or no rise, NIDDK says. It adds that the test may not be accurate in people who have had secondary adrenal insufficiency for a shorter time, because their adrenal glands can still respond.

The test comes in two doses. A 2023 review describes a standard dose of 250 µg and a low dose of 1 µg, and says studies show the low-dose version is not superior in diagnostic accuracy, and can be affected by small errors in diluting and injecting it. A 2026 study notes that the ACTH test has been validated against the insulin tolerance test and is safer, more convenient and free of contraindications.

Steps 4 and 5: follow-ups

If the stimulation test isn’t clear, or a pituitary problem is suspected, NIDDK lists an insulin tolerance test and a CRH stimulation test. The insulin tolerance test deliberately lowers blood sugar, needs a health professional present throughout, and isn’t safe for people with heart disease, a history of seizures and other serious illnesses. Once the diagnosis is made, antibody blood tests, a CT scan of the abdomen and an MRI of the pituitary look for the cause.

What a low morning cortisol leads to

A low morning value doesn’t diagnose anything by itself. It leads to more testing. The usual next steps are ACTH, then a stimulation test. The 2026 study says that when a morning value is neither clearly low nor clearly sufficient, a stimulation test is recommended.

Why not just apply a cut-off? Three reasons, all from the sources:

• The method matters. The 2026 study says the cut-offs in current guidelines were derived from older cortisol assays, and that a newer, more specific immunoassay gave different thresholds. A 2024 review in Endocrine Reviews cites a study in which five automated immunoassays read 1.08 to 1.36 times higher than a mass spectrometry reference (Endocrine Reviews, 2024). Use the range printed on your own report. The normal range page lists published ranges and the units converter helps with nmol/L.
• The sample reflects total cortisol. That includes cortisol attached to carrier proteins. Oral estrogens and pregnancy raise those proteins, giving a higher total cortisol. Nephrotic syndrome lowers them, giving a lower one, which can mislead.
• Things in the sample. Some synthetic steroids, such as prednisolone, can be read as cortisol by certain immunoassays, and biotin can interfere with some immunoassays. Tell the lab and your clinician about every medicine and supplement you take. Don’t stop any of them to prepare, especially a steroid. Ask the prescriber.

Low cortisol and blood pressure

NIDDK lists low blood pressure that drops further when you stand up, causing dizziness or fainting, among the symptoms of adrenal insufficiency. A 2013 paper on delayed diagnosis reports substantial low blood pressure or shock in people who were in an adrenal crisis or close to one. That is an emergency.

A blood pressure reading is not a cortisol test, though. Low blood pressure has many other causes, and a normal reading doesn’t rule adrenal insufficiency out. If you have dizziness on standing along with long-lasting tiredness, weight loss or loss of appetite, tell a clinician. The cortisol and blood pressure page covers the link.

If you are thinking of ordering a test

A morning cortisol with a later sample can give you a number to bring to a clinician if you have no emergency signs. It is a first step and not a work-up. An unusual result still needs ACTH or a stimulation test, which a clinician arranges. A result inside the lab’s printed range doesn’t rule adrenal insufficiency out either, so if symptoms continue, tell a clinician.

If you order a single cortisol, check what time of day the order asks for. The seller’s page for its morning-and-later test says the morning draw should typically be between 7 and 9 a.m. It gives 3 to 5 p.m. as the later window, but also says the second sample is taken “at night”, and it doesn’t say whether the draws are one visit or two. Check this before you order and follow the timing on your lab order. The page states no fasting rule, so follow the instructions on your order too.

The seller’s ACTH page gives no draw time or handling instructions. Since ACTH is usually compared with a cortisol level and samples need careful handling, ask the lab how it wants the sample.

• Cortisol AM and PMAdds a later sample to the morning one. Check the timing first $129 See this test at HealthLabs
• ACTHOften drawn with a morning cortisol. Follow the lab's handling instructions $49 See this test at HealthLabs

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

Tests for tiredness covers what else is commonly checked first when the main symptom is feeling tired.

When to see a clinician

NIDDK’s advice is that if you always feel tired, weak or are losing weight, you should ask whether you might have adrenal insufficiency, and that early treatment can help avoid an adrenal crisis. In a small single-center study of 60 people with primary adrenal insufficiency in Poland, 26 were first diagnosed during or just before an adrenal crisis (Int J Endocrinol, 2013). That is a reason to raise persistent symptoms, not a reason to assume your own tiredness is adrenal. See low cortisol symptoms.

Questions people ask

What does a low AM cortisol mean?

On its own, it means more testing. A clinician looks at it alongside ACTH, your symptoms, your medicines and the lab’s method. Many things can lower or shift a single reading.

Is there a test for low cortisol?

Yes. The tests are a morning blood cortisol, ACTH, and a stimulation test, with other tests to follow if needed. A cortisol test alone can’t identify the cause of an abnormal level, MedlinePlus says.

Can I test for low cortisol at home?

Saliva kits exist, but the tests that diagnose adrenal insufficiency are blood tests and stimulation tests done under a clinician. MedlinePlus says at-home tests are not a replacement for a provider’s guidance and that you should follow up with your provider whatever the result.