8 min - BioSense Team - 2026-10-14
- level:understanding
- cortisol élevé
- prise de sang cortisol
- taux de cortisol normal
- cortisol salivaire
Cortisol is probably the hormone that is hardest to measure correctly. Its level changes several-fold depending on the time of the blood draw, and a number of common situations distort the result without anyone giving it a thought. Here is what a cortisol blood test measures, what can affect it, and why a single number almost never allows a conclusion.
Your cortisol result has come back above the range printed on the report. You are trying to understand what that means, and you come across a great deal of content that links high cortisol directly to stress.
The biological reality is less simple. A cortisol test is read with particular precautions, and an out-of-range result on a single blood draw does not say much in itself.
This article explains why.
What cortisol does in the body
Cortisol is produced by the adrenal glands, two small glands sitting above the kidneys. Its production is driven by a chain that starts in the brain: the pituitary gland sends a hormone called ACTH to the adrenals.
Its role goes far beyond the stress response. According to MedlinePlus (National Library of Medicine), cortisol plays a part in blood pressure control, immune function, the metabolism of fats, carbohydrates and protein, nervous system function and bone growth. It also follows a daily rhythm.
It is that rhythm which explains the main difficulty of the test.
High cortisol symptoms: what leads a doctor to order the test
A lasting excess of cortisol is called hypercortisolism; when marked and prolonged, it is known as Cushing's syndrome. It is rare, and it is what the test looks for, when several signs point that way:
- weight gain on the belly, face and back of the neck, while the arms and legs stay thin;
- a round, red face;
- thin skin, bruising from minor bumps, wide purple stretch marks;
- weak thigh and shoulder muscles, making it hard to get up from a chair;
- rising blood pressure or blood sugar, weaker bones;
- irregular periods, new facial hair or acne;
- sleep and mood problems.
Taken one by one, these signs are common and unrelated to cortisol. After 40, weight gain, poor sleep and mood changes often come with perimenopause. What alerts a doctor is how they add up, how they worsen over months, and the more specific signs: easy bruising, wide stretch marks, muscle weakness. They also think of cortisol when signs look like the side effects of steroid medicine in someone who takes none.
How do you know if you have too much cortisol? Not from a single number. Is your level normal? The range on your report applies to a morning sample, at the time noted, and varies with the lab's method. Even above it, a single test confirms nothing, for the reasons explained below. The answer lies in specific tests, ordered and interpreted by your doctor. The most useful thing you can bring them is the timeline of your signs.
Why the time of the blood draw changes everything
Cortisol production follows a marked daily cycle. It is normally highest in the morning, then much lower by late afternoon, and lower still late at night.
One and the same healthy person can therefore show widely differing values depending on the time of the blood draw.
Practical consequence: a cortisol test only makes sense if the exact time of the draw is known. That is why the test is usually ordered early in the morning. MedlinePlus gives, as an example, a normal range of 5 to 25 mcg/dL (138 to 690 nmol/L) for a sample taken at 8 a.m., and adds that normal values depend on the time of day and the clinical context. Each lab publishes its own range.
Key point - Cortisol varies considerably over the course of the day. A test without a precise time of draw is hard to interpret, and comparison with a morning reference range assumes a morning sample.
Why a single blood test is not enough
Here is the point that most consumer content skips.
To look for excess cortisol (Cushing's syndrome), a one-off blood test is not the test of choice. France's current practice reference, the 2023 national diagnosis and care protocol (PNDS), does not list it among first-line tests, and the Endocrine Society's 2008 guideline, long the international reference, explicitly recommended against using a random serum cortisol for this purpose.
MedlinePlus also lists stress and acute illness among the things that can raise a cortisol result, on top of the variation from one moment to the next. The morning blood test does, on the other hand, keep its usefulness for another question, that of too little cortisol. The logic is different and so are the thresholds.
What distorts the result without your knowing
Several very common situations change the level measured.
The combined pill and estrogen treatments
In the blood, cortisol circulates mostly bound to a transport protein called CBG. The standard blood test measures total cortisol, that is, the bound fraction and the free fraction added together.
Now, estrogens increase the amount of that transport protein. As a result, the total cortisol measured is higher in someone on the combined pill or on oral estrogen therapy, while the active fraction may not have changed. The Endocrine Society's 2008 guideline listed estrogens among the drugs that may falsely elevate cortisol results.
This point is little known and it concerns a great many people.
Pregnancy
Cortisol results are also harder to read during pregnancy. For the initial search for Cushing's syndrome in pregnancy, the Endocrine Society's 2008 guideline recommended urine free cortisol and recommended against dexamethasone testing.
The corticosteroids you are already taking
This is the most important element, and the most often forgotten. According to NIDDK, the most common cause of Cushing's syndrome is the long-term, high-dose use of cortisol-like medicines called glucocorticoids.
The Endocrine Society's 2008 guideline placed a thorough drug history first, ahead of any test. MedlinePlus notes that these medicines come in many forms: pills, skin creams, eye drops, inhalers and joint injections. Depending on the medicine and the test, they can push the result up or down.
Mention them all, including a past injection, even if it seems old or unrelated.
Night work and shifted hours
The cortisol cycle follows the sleep-wake rhythm. The 2021 international consensus on Cushing's disease notes that the dexamethasone test may be preferred for shift workers and people with uneven sleep schedules. The usual reference ranges, built on a conventional rhythm, may not apply in the same way.
Certain medications and alcohol
Several treatments change how the body handles the dexamethasone used in suppression tests. The Endocrine Society's 2008 guideline listed certain seizure medicines, such as phenobarbital, phenytoin and carbamazepine, and the antibiotic rifampin. Alcohol use disorder, obesity and psychiatric disorders can also activate the same hormonal axis.
Key point - The combined pill, pregnancy, corticosteroids in all their forms, night work: these situations can change a cortisol test without any adrenal disorder being involved. Your doctor needs to know about them before reading the result.
Cortisol shows it well: the same result changes meaning according to your treatments, your hours and your situation. That is exactly what BioSense does. Import your blood test, record your context, and receive a plain-language reading of each biomarker that takes it into account. Your data is hosted on servers located in France.
[→ Import my blood test](/en/onboarding/upload)
Cortisol blood test: how it is done
Cortisol is not part of standard blood work. A CBC, a lipid panel or a TSH test often go out together on the same order; cortisol is ordered separately, when a clinical situation calls for it.
The blood draw is usually done early in the morning, and the time is recorded. Follow the instructions you are given. MedlinePlus says you may be asked to avoid vigorous exercise the day before and to temporarily stop certain medicines, such as seizure medicines, estrogen and steroids. Never stop a medicine unless your doctor tells you to. If another test on the same order requires fasting, the constraint comes from that test.
A single cortisol level, even clearly above the range, therefore establishes nothing on its own. It opens a workup, which rests on other tests.
The tests that actually evaluate cortisol
When Cushing's syndrome is suspected, France's 2023 PNDS, like the Endocrine Society's 2008 guideline, recommends starting with one or more of these tests. Your doctor chooses according to your situation.
- 24-hour urine free cortisol. It involves collecting all your urine over a complete day. It reflects overall production. Guidelines ask for at least two collections.
- Late-night salivary cortisol. The sample is taken at home, late in the evening, using a dedicated kit. It checks whether the level falls normally at night. It is also repeated, at least twice.
- The dexamethasone suppression test. You take a small dose of a synthetic steroid at night, then have your cortisol measured the next morning. The usual cutoff for a normal response is below 1.8 mcg/dL (50 nmol/L).
One thing these tests have in common deserves to be noted: none of them is a simple morning blood draw. The Endocrine Society's 2008 guideline also recommended against widespread testing beyond people with suggestive features, such as multiple and progressive signs of the syndrome, or an incidental adrenal mass. An abnormal result leads to an endocrinologist, not to a conclusion.
In France, late-night salivary cortisol has one particularity: it is not on the national list of lab tests, so it is not reimbursed. France's PNDS itself regrets this, noting that the test is recognized internationally as having greatly simplified and improved diagnosis. It adds that the usual values must be adapted to the lab's testing method.
Low cortisol: what if your level is low?
The opposite question exists and does not obey the same logic.
A clearly low morning cortisol can point toward adrenal insufficiency. According to NIDDK, the most common symptoms are fatigue, muscle weakness, loss of appetite, weight loss and abdominal pain. Low blood pressure and abnormal sodium or potassium can also appear.
Here, unlike the search for an excess, blood testing is the starting point. The Endocrine Society (2016) prefers a stimulation test with an injection of cosyntropin, a synthetic form of ACTH. A peak cortisol below 18 mcg/dL (500 nmol/L), depending on the assay, indicates adrenal insufficiency. If that test is not feasible, a morning cortisol below 5 mcg/dL (140 nmol/L) with ACTH is a preliminary signal until it can be done.
Long-term steroid use is a frequent setting for this question. Suddenly stopping steroid medicines can cause adrenal insufficiency, according to NIDDK, and a 2024 guideline from the European Society of Endocrinology and the Endocrine Society covers how to assess recovery. Do not stop a steroid on your own. Severe symptoms may signal an adrenal crisis, which is a life-threatening emergency.
What cortisol does not measure
It has to be said plainly, because it is the main confusion on this subject: a cortisol test does not measure your level of stress.
There is no blood test able to quantify the stress you feel, or to diagnose burnout, anxiety or depression. Those assessments are clinical and rest on listening and on the tools used by doctors and psychologists.
The same goes for "adrenal fatigue". The Endocrine Society says no scientific proof exists to support it as a true medical condition, and that no test can detect it. The real risk is missing the actual cause of your symptoms, such as depression, sleep apnea or true adrenal insufficiency. The FDA does not approve dietary supplements before they are sold, and "adrenal support" products are no exception.
If your concern is above all about prolonged stress and its effects on your health, our article devoted to chronic stress approaches that question from another angle.
Key point - Cortisol is not an indicator of the stress you feel. It is a hormonal marker, ordered for specific clinical signs and interpreted by a doctor.
The BioSense method
Cortisol illustrates a rule that holds for many biomarkers: the number is not enough. The time of the blood draw, your current treatments, your birth control and your working hours can completely change the reading of the same result.
BioSense sets each biomarker against what you tell us about your situation, then follows its trend from one blood test to the next. It is that combination which turns a number into information that is useful for your next appointment.
*ChatGPT answers you. BioSense knows you.* *BioSense, your prevention companion.* BioSense does not provide a diagnosis and does not replace your doctor. It is a prevention companion that helps you understand, ask the right questions and act day to day.
Preparing for your appointment: three useful questions
If you have a cortisol result in hand, these three questions help to frame the appointment:
- My sample was taken at this time. Is that compatible with the reference range used to interpret it?
- I am currently taking this treatment, and I received an injection or used a cortisone cream at this time. Could that explain this result?
- Given my symptoms, does this result justify going further, or can we leave it there?
Mentioning hormonal birth control, a hormone treatment or work on shifted hours often changes the reading of the result.
Frequently asked questions
What does high cortisol mean on a blood test?
A high cortisol on one blood test does not establish a diagnosis. It can reflect the time of the draw, stress, acute illness, estrogen or a steroid medicine. If your doctor suspects Cushing's syndrome, other tests are used to confirm or exclude it.
What is a normal cortisol level in the morning?
MedlinePlus gives 5 to 25 mcg/dL (138 to 690 nmol/L) as an example for a sample taken at 8 a.m. Normal values depend on the time of day, the clinical context and the lab. The range printed on your report is the one that applies.
What are the symptoms of high cortisol?
According to NIDDK, signs of Cushing's syndrome include weight gain, a round face, thin arms and legs, easy bruising, wide purple stretch marks and weak muscles, and periods may become irregular. Symptoms vary and not everyone has them. Talk with your doctor if several appear and progress.
Does stress raise cortisol levels on a blood test?
Yes, stress and acute illness can raise a cortisol result, but a cortisol test does not measure the stress you feel. A single level is not a useful way to assess long-lasting stress. Your doctor can judge whether a test is useful in your case.
*This article is strictly informational and constitutes neither medical advice nor a diagnosis. For any question about your health, consult your doctor.*
Import your blood test and receive a plain-language reading of each biomarker, set in the context of your personal situation. Your data is hosted on servers located in France.
[→ Import my blood test](/en/onboarding/upload)
Sources and methodology
France
- Haute Autorité de santé (HAS). Syndrome de Cushing, national diagnosis and care protocol (PNDS), developed by the French reference centre for rare adrenal diseases following HAS methodology, published on has-sante.fr on 23 March 2023, with a 2022 update rationale. HAS states that it did not validate this protocol and did not take part in drafting it. HAS, including the summary for general practitioners, January 2023
International
- Fleseriu M, Auchus R, Bancos I, et al. Consensus on diagnosis and management of Cushing's disease: a guideline update. Lancet Diabetes & Endocrinology, 2021;9(12):847-875. Pituitary Society consensus covering Cushing's disease of pituitary origin only, not adrenal or ectopic causes. PMC
United States
- Historical reference. Endocrine Society. Nieman LK, et al. The Diagnosis of Cushing's Syndrome: An Endocrine Society Clinical Practice Guideline. Journal of Clinical Endocrinology & Metabolism, 2008;93(5):1526-1540. PMC
- Endocrine Society. Diagnosis of Cushing's Syndrome Guideline Resources. Endocrine Society
- Endocrine Society. Bornstein SR, et al. Diagnosis and Treatment of Primary Adrenal Insufficiency: guideline resources, 2016. Endocrine Society
- European Society of Endocrinology and Endocrine Society. Glucocorticoid-Induced Adrenal Insufficiency: guideline resources, 2024. Endocrine Society
- Endocrine Society. Adrenal Fatigue. Patient information. Endocrine Society
- MedlinePlus, National Library of Medicine. Cortisol blood test. MedlinePlus
- MedlinePlus, National Library of Medicine. Cortisol Test. MedlinePlus
- NIDDK. Cushing's Syndrome. NIDDK
- NIDDK. Adrenal Insufficiency & Addison's Disease. NIDDK
- FDA. Questions and Answers on Dietary Supplements. FDA
*Methodological note: decision thresholds for cortisol vary with the lab's technique and the clinical context. Those mentioned here are quoted to explain how the tests work, not to supply a reading grid.*
*BioSense methodology: our content is based on guidance from US authorities and medical societies (such as the USPSTF, CDC, NIH, FDA, ACC/AHA and ADA), UK bodies (NICE, NHS), European societies and the WHO. Sources are listed by country, and differences between countries are stated when they matter.*