What is cortisol?
Your adrenal glands, two small glands above your kidneys, make cortisol on orders from your brain, in a rhythm steered by the clock. In the last hours of the night production rises, in the half hour after waking it peaks, and after that it falls over the day to a quarter of the morning value around midnight. That rhythm is the subject itself: cortisol frees sugar and fat, keeps your blood pressure and your blood sugar up, dampens inflammation and readies your body to act. It is the hormone you get up with, and the hormone that shoots up within minutes with an infection, an operation or a fright. That is why a single value cannot say whether you are stressed. Cortisol moves with the hour, with sleep, with a meal, with exertion and with the draw itself, and the labs build that rhythm into their bands: the morning band starts about twice as high as the late-afternoon band. A value that is normal in the morning falls above the band in the afternoon, and the other way round. What a cortisol value can do is show whether the adrenal glands make too little, which gives a deficit at the morning peak, or far too much, which wipes out the rhythm. Your report shows cortisol in nmol/L, with the time alongside. Normal in the morning between 06.00 and 10.00 is about 172 to 497 nmol/L and in the late afternoon between 16.00 and 20.00 80 to 286 nmol/L, where the labs overlap. One of the four reports in µmol/L; converted, the figures are the same.
Why is cortisol relevant?
Most people who have cortisol measured want to know whether their stress has become measurable. That is exactly what this value cannot do. No blood value exists for being burnt out, no lab publishes a limit for it, and a cortisol in the band does not rule out exhaustion while a value outside it does not prove it. Anyone under chronic pressure often has a flatter curve, a lower morning peak and an evening that no longer falls, but you only see that with several measurements over the day, usually in saliva, and even then it is a pattern and not a diagnosis. What the value does serve is the adrenal gland itself. An adrenal gland that makes too little gives tiredness, nausea, weight loss, low blood pressure, a craving for salt and a tanned skin, and then the morning value is low where it should be high. That is Addison's disease, rare but dangerous, and the most common reason it happens is a course of prednisone that has just stopped, after which the adrenal glands need weeks to get going again. An adrenal gland that makes far too much gives a round face, belly fat with thin arms and legs, purple stretch marks, a high blood pressure and a high blood sugar, and then the evening value stays high. That is Cushing's syndrome, and the first test for it is not a morning value but an evening value or a test after a dexamethasone tablet. For anyone who is healthy, cortisol is mainly a value to understand rather than to measure. The rhythm is the lever: light in the morning, a fixed time of getting up, no screens late in the evening, and sleep that lasts long enough keep the peak sharp and the evening low. That is what you feel as energy in the morning and calm in the evening.
Cortisol reference ranges
What counts beside the number:
- The time of the draw, because without a time the value cannot be read, and the band of that daypart
- How you slept, whether you were ill, trained hard or dreaded the draw
- Whether you take the pill or are pregnant, because that lifts the total without more active cortisol
- Whether you take prednisone, a steroid inhaler or a steroid ointment or have just stopped
- Symptoms that fit too little, tiredness, nausea, low blood pressure, a craving for salt, or too much, a round face, belly fat, stretch marks, high blood pressure
- DHEA-S from the same draw, which does not move with the clock, and sodium, potassium and glucose
There is no national reference value for cortisol, and the bands above are about the time of the draw, not about resilience: no lab publishes a limit for stress or burnout, and none exists. Always read the value with the time alongside, against the band of that daypart. Mention the pill, a pregnancy and any use of prednisone or another steroid, because those shift the result without the adrenal glands doing anything.
What Dutch labs actually use
Three of the four labs publish no single reference value for cortisol but one per daypart, and the fourth prints one band for the whole day, in a different unit. Star-shl and Certe hold exactly the same figures: 133 to 537 nmol/L in the morning and 68 to 327 in the late afternoon. Clinical Diagnostics is narrower at both ends, 172 to 497 and 74 to 286. Unilabs publishes one band for the whole day and reports in µmol/l: 0.080 to 0.555, which converts to 80 to 555 nmol/L; whoever sets two reports side by side without seeing the unit reads a thousand-fold difference that is not there. The splitting labs set the morning floor roughly double the afternoon one, and that is the subject itself: cortisol follows the clock.
172 – 497nmol/L
Between 80 and 172 and between 497 and 555 it differs per lab, because each lab sets its limits on its own method and population. Above 555 every lab calls it abnormal.
Every age, per lab
| Laboratory | Group | Reference range |
|---|---|---|
| Unilabs(Saltro, Medlon, SHO, Atalmedial)2026 | Whole day | 0.080–0.555 µmol/l |
| Whole day | 0.080–0.555 µmol/l | |
| Star-shl2026 | Morning (8.00) | 133–537 nmol/L |
| After midday (18.00) | 68–327 nmol/L | |
| Certe2026 | 06.00–10.00 | 133–537 nmol/L |
| 16.00–20.00 | 68–327 nmol/L | |
| Clinical Diagnostics2026 | 06–10 | 172–497 nmol/L |
| 16–20 | 74–286 nmol/L |
Each band as the lab publishes it, retrieved in 2026, unless marked otherwise.
Cortisol high or low: what it means
A low value belongs to the end of the day: cortisol falls over the day to a quarter of the morning value, and a low late-afternoon value is not a finding but the rhythm itself. A low morning value is what counts. The most common reason is a course of prednisone or another steroid, also an inhaler or an ointment, that stopped shortly before: the adrenal glands are then still quiet and need weeks to get going again. Rare is Addison's disease, in which the adrenal glands themselves fail, or a pituitary that no longer gives the order; a low morning value with symptoms of tiredness, nausea, low blood pressure and a craving for salt should be investigated the same week with a stimulation test. A high value is first a question about the time and the circumstances. Setting a morning value beside the late-afternoon band turns the rhythm into a deviation. A draw after a bad night, a hard training session, an infection, a fright or fear of the needle lifts the value, and that is cortisol doing its job. The pill and a pregnancy lift the total because there is more binding protein, without there being more active cortisol. Prednisolone and prednisone are sometimes mistaken for cortisol by the test and give a falsely high result. A genuinely too high cortisol, Cushing's syndrome, is rare and stands out by the picture around it; the evening value that does not fall is then the clue. What you do about it: nothing to a single value, a lot to the rhythm. Get up around the same time every day and seek daylight in the first hour, because that sets the morning peak sharp. Sleep long enough and avoid bright light and screens late in the evening, so the evening value can fall. Move during the day and not just before sleep. Caffeine late in the afternoon keeps cortisol high. When a course of prednisone stops, it is tapered slowly so the adrenal glands get time. With a suspicion of Addison's or Cushing's a single value is not enough, and a stimulation or suppression test follows. Always read cortisol with the time alongside, and beside DHEA-S, which comes from the same adrenal glands but does not move with the clock; together they show what is rhythm and what is store. Sodium, potassium and glucose show whether a low or high value is already working through.
What lowers it
Usually the rhythm itself; a low morning value is what counts.
| Cause | How often |
|---|---|
| Drawn later in the dayCortisol falls over the day to a quarter of the morning value; low in the late afternoon is not a finding but the rhythm | Often |
| Adrenal glands still quiet after a course of prednisonePrednisone, also as an inhaler or ointment, shuts down the body's own production; after stopping, the adrenal glands need weeks to months to get going again | Sometimes |
| Addison's diseaseThe adrenal glands themselves fail, usually through the immune system; tiredness, nausea, low blood pressure, a craving for salt and a tanned skin go with it, and a stimulation test gives the answer | Rare |
| A problem in the pituitaryThe brain no longer gives the order; then other hormones are usually low too | Rare |
What raises it
First the question which daypart you compare, then what was going on that day.
| Cause | How often |
|---|---|
| The wrong daypart as comparisonSetting a morning value beside the late-afternoon band turns the daily rhythm into a deviation; 327 nmol/L is the late-afternoon ceiling of two labs and simply normal in the morning | Often |
| Stress or too little sleepA bad night, a hard training session, an infection, a fright or fear of the needle lift the value; that is cortisol doing its job | Often |
| Hormonal contraceptionOestrogen makes the liver produce more binding protein; the total rises without there being more active cortisol, and a pregnancy does the same | Often |
| Prednisolone or prednisoneAre sometimes mistaken for cortisol by the test and give a falsely high result; mention corticosteroids at the draw | Sometimes |
| Cushing's syndromeThe adrenal glands or a growth make far too much; a round face, belly fat with thin limbs, stretch marks and a high blood pressure go with it, and an evening value that does not fall is the clue | Rare |
How does a cortisol blood test work?
- Referral
- Not needed. You can have cortisol measured yourself, but know beforehand what you want to know: for stress or burnout no blood value exists, and for the adrenal gland itself the morning value is the first step.
- Fasting
- Not strictly needed, though a meal lifts the value slightly; preferably have blood drawn fasting in the morning.
- When
- Between 08.00 and 09.00, one to two hours after waking, after a normal night, without a hard training session the day before and not during an infection. For a series always at the same time.
- The draw
- One tube of blood from a vein in your arm, with the time noted alongside. Sit for a quarter of an hour before the draw, because fear of the needle lifts the value. Mind the unit: one lab reports in µmol/L.
- Repeating
- Only when the question asks for it: a low morning value is followed by a stimulation test, a suspicion of too much by an evening value or a suppression test. A healthy morning value need not be repeated.
- Where to draw
- You can draw at 250+ locations near you, no referral needed. See the locations
Frequently asked questions
What is cortisol?
The hormone your adrenal glands use to start your body up every morning and to put it on alert with an infection, an operation or a fright. It frees sugar and fat, keeps your blood pressure and blood sugar up and dampens inflammation. It follows the clock: it peaks in the half hour after waking and falls over the day to a quarter of the morning value. That rhythm is what you feel as energy in the morning and calm in the evening.
What is a normal cortisol value?
That depends on the time. In the morning between 06.00 and 10.00 the value where the labs overlap sits between 172 and 497 nmol/L, in the late afternoon between 16.00 and 20.00 between 80 and 286 nmol/L. A value that is normal in the morning falls above the band in the afternoon, and the other way round. Without a time a cortisol value therefore cannot be read, and a morning value is the first step for the question whether the adrenal glands make enough.
Can a cortisol test show that I am burnt out?
No. No blood value exists for being burnt out, no lab publishes a limit for it, and a cortisol in the band does not rule out exhaustion while a value outside it does not prove it. Anyone under chronic pressure often has a flatter curve, but you only see that with several measurements over the day, usually in saliva, and even then it is a pattern and not a diagnosis. How you sleep, how you feel and what you can handle say more than the number.
What does a high cortisol mean?
First the question which daypart you compare and what was going on that day. A morning value beside the late-afternoon band turns the rhythm into a deviation, and a bad night, a hard training session, an infection or fear of the needle lift the value without anything being wrong. The pill and a pregnancy raise the total because there is more binding protein, and prednisone gives a falsely high result. A genuinely too high cortisol, Cushing's syndrome, is rare and stands out by a round face, belly fat, stretch marks and a high blood pressure.
What does a low cortisol mean?
In the late afternoon nothing: the value falls over the day to a quarter of the morning, and low is then the rhythm itself. A low morning value does count. Usually it comes from a course of prednisone, also as an inhaler or ointment, that has just stopped and leaves the adrenal glands still quiet. Rare is Addison's disease, in which the adrenal glands themselves fail; tiredness, nausea, low blood pressure, a craving for salt and a tanned skin go with it, and then a stimulation test follows the same week.
Why is cortisol higher in the morning?
Because in the last hours of the night your brain orders the adrenal glands to ready the body for the day: blood sugar up, blood pressure up, alertness on. In the half hour after waking the value peaks, and after that it falls gradually until around midnight. Light in the morning and a fixed time of getting up keep that peak sharp; bright light and screens late in the evening keep the evening value high and disturb sleep.
How do I keep my cortisol rhythm healthy?
With the clock as lever. Get up around the same time every day and seek daylight in the first hour, because that sets the morning peak. Sleep long enough, dim the light in the evening and put screens away, so the evening value can fall. Move during the day, not just before sleep, and drink no more caffeine after noon. With persistent pressure, rest, relaxation and dosing the load help more than any measurement.
Can medication affect the result?
Yes, in three ways. Prednisone and other steroids, also as an inhaler or ointment, shut down the body's own production, so a low morning value after stopping is to be expected and recovers in weeks to months. Prednisolone and prednisone are sometimes mistaken for cortisol by the test and then give a falsely high result. And the pill and a pregnancy make the liver produce more binding protein, so the total rises without there being more active cortisol. Mention them all at the draw.
Which tests include cortisol?
Cortisol is measured in the Cortisol day rhythm module, on top of another draw. It is not orderable yet.
Related biomarkers
Sources
- 1.Unilabs, test catalogue (Dutch): cortisol. 2026. bepalingenklapper.nl
- 2.Unilabs, test catalogue (Dutch): cortisol at approx. 09.00. 2026. bepalingenklapper.nl
- 3.Star-shl, test catalogue (Dutch): cortisol. 2026. star-shl.nl
- 4.Certe, test catalogue (Dutch): cortisol. 2026. bepalingenwijzer.certe.nl
- 5.Clinical Diagnostics, lab guide (Dutch): cortisol in serum. 2026. clinicaldiagnostics.nl
Educational information only, not medical advice. Consult a healthcare professional for clinical decisions.
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Cortisol is measured in the Cortisol day rhythm module, on top of another draw. It is not orderable yet.
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