A cortisol level in blood only means something once you know two things: what time the blood was drawn, and which reference range your laboratory uses. Without both, the number cannot be read. Cortisol follows a daily rhythm, and the ranges differ per method.
That sounds like a technical footnote. It is the single most important thing to know about this value, and it is the part most pages leave out.
Below: what the numbers mean, why they differ per lab, and why one isolated measurement adds less than you would hope when stress complaints persist.
What is a normal cortisol level?
For blood drawn in the morning, roughly between 06:00 and 10:00, Dutch laboratories often use a range around 171 to 497 nmol/L. Other labs publish roughly 200 to 700 nmol/L for that same morning window. Both are correct for their own method.
Put those side by side and the problem is obvious. A value of 620 nmol/L is clearly raised at one lab and unremarkable at the other.
| Time of draw | What labs often use | Why it matters |
|---|---|---|
| Morning, 06:00 to 10:00 | around 171 to 497 nmol/L | The peak of your daily curve |
| Morning, different lab or method | around 200 to 700 nmol/L | Same time, different limits |
| Late afternoon | clearly lower than your morning value | The curve has already fallen |
| Around midnight | the lowest point of the day | A morning range does not apply |
So always use the range printed on your own result, together with the draw time. Do not compare your value against a number from an article, including this one.
Why does your cortisol level change by the hour?
Cortisol follows a fixed daily rhythm. It is highest shortly after waking, falls through the day and reaches its lowest point around midnight. The same value can more than halve within a day without anything being wrong.
On top of that, cortisol is released in pulses. Two tubes of blood drawn half an hour apart will not give the same number.
That is why laboratories record the draw time for this test. Without it, the range cannot be applied.
Can you measure cortisol in blood?
Yes, cortisol is readily measured in blood, and that is the usual route when a doctor wants to investigate a suspected adrenal condition. The draw is then preferably done in the morning, because the morning range is the best studied.
It can also be measured in saliva and in urine collected over twenty-four hours. Which form is useful depends on the question your doctor wants to answer, not on which test is easiest to order.
The follow-up question matters more than the technique: what will you do with the number?
Why does a single cortisol level say little about stress?
When stress and exhaustion complaints persist, one isolated cortisol measurement adds little in practice. Research among people with stress-related exhaustion found no difference in cortisol profile compared with healthy controls, and no change during treatment either. The authors concluded these measurements do not appear suitable as a biomarker for burnout in routine practice (PMID 26159953).
A study of 401 workers did find associations between the daily cortisol pattern and symptoms of distress, low mood and burnout, but described those associations as modest (PMID 24469265).
A meta-analysis covering 179 associations from 80 studies showed that a flatter daily cortisol slope is linked to poorer outcomes in ten of twelve areas studied (PMID 28578301). That describes patterns across groups, measured at several time points. It is a different thing from a statement about your one tube of blood.
We therefore advise against this test for complaints that fit stress, burnout or fatigue, unless your doctor specifically asks for it. That is stated on our own cortisol test as well.
When is a cortisol level worth measuring?
A cortisol measurement belongs with a specific clinical question. Think of investigating a suspected over- or underactive adrenal gland, where the clinical picture and its course are the reason, and the measurement is part of a larger workup.
In that situation your doctor decides the timing, the form of the test and what follows. Thuisarts describes that route and when further investigation is appropriate.
Outside such a question the number mostly produces worry. A normal result does not remove your complaints, and a slightly off result without context rarely leads anywhere.
What is worth measuring when complaints persist?
With long-standing fatigue or a burnt-out feeling, it is more usual to first check the things a blood value can actually judge well. Thyroid function, anaemia and iron stores are often near the front, because they cause complaints that closely resemble stress.
The NHG guidelines describe which investigation fits which complaint. Discuss that route with your GP, because the order depends on your own history.
To understand what a raised result might mean, read high cortisol: symptoms of chronic stress. If you are looking for what you can do yourself, lowering cortisol with food covers that. Background on the measurement itself is on our cortisol page.
References
- Sjors A, Jonsdottir IH. No alterations in diurnal cortisol profiles before and during the treatment in patients with stress-related exhaustion. International Journal of Occupational Medicine and Environmental Health, 2015. PMID 26159953.
- Marchand A, Durand P, Juster RP, Lupien SJ. Workers' psychological distress, depression, and burnout symptoms: associations with diurnal cortisol profiles. Scandinavian Journal of Work, Environment and Health, 2014. PMID 24469265.
- Adam EK, Quinn ME, Tavernier R, McQuillan MT, Dahlke KA, Gilbert KE. Diurnal cortisol slopes and mental and physical health outcomes: a systematic review and meta-analysis. Psychoneuroendocrinology, 2017. PMID 28578301.
- Thuisarts, information on adrenal glands and fatigue complaints.
- NHG guidelines, investigation of persistent fatigue.
Every blood test result at Lunara includes a professional assessment by a BIG-registered doctor. For treatment decisions, discuss your results with your GP.
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