Cortisol Test: 8am Blood Test, Saliva and Home Kits, What They Really Measure

A level that moves

Cortisol is not measured like cholesterol, it changes from hour to hour.

Cortisol is a hormone made by the adrenal glands, two small glands that sit on top of the kidneys. It is often called the “stress hormone”, but its role is much broader: it helps mobilise sugar, regulate blood pressure, modulate inflammation and set the rhythm of the day. You cannot live without cortisol.

Its production follows a 24-hour rhythm, controlled by the brain. It is at its lowest around midnight, rises again in the second half of the night, peaks on waking, then falls slowly until the evening. On top of this rhythm, every stressor, whether exercise, a meal or bad news, causes small spikes.

The practical consequence: a result only means something in relation to the time the sample was taken. A cortisol level that is “normal” at 8am would be too high at midnight. That is why cortisol is never measured at a random time of day. To understand the link with your morning cup, see our article on coffee and cortisol.

The four measurements

Blood, saliva, urine, hair: each test answers one question.

There is not one cortisol test, but several. They do not measure the same thing, or over the same period. The right test depends on what you are looking for: a deficiency, an excess, or a trend over several months.

There are also dynamic tests, carried out under medical supervision: the dexamethasone suppression test for an excess, and the Synacthen® test for a deficiency.

Remember one simple idea: the morning blood test is good at spotting cortisol that is too low, but poor at spotting cortisol that is too high. For an excess, it is the evening and the whole day that tell the story.

Cortisol at 8am: normal ranges

Normal cortisol levels at 8am: a wide range.

A blood cortisol test is usually done between 7am and 9am, fasting, after a normal night. The laboratory gives its result with its own reference values, because they depend on the technique used. Always compare your figure with the ranges printed on your report, not with those on a website.

The range is wide because healthy people are very different from one another, and because the same person varies from one day to the next. A figure at the top of the range is not “bad”, and a figure at the bottom is not “weak”. What matters is being clearly outside it, and above all having symptoms that go with it.

Watch the units: the same result can be written as 400 nmol/L or 14.5 µg/dL. A lot of worry comes from comparing two different units.

What skews the result

The pill, timing, the needle: the most common pitfalls.

A cortisol result can fall outside the normal range without any disease being involved. Before you worry about a figure, check whether one of these situations applies to you.

• The pill and oestrogens. They increase the protein that carries cortisol in the blood. Total cortisol then looks high, while active cortisol is normal. Pregnancy does the same.
• Corticosteroids. Tablets, inhalers, creams, injections: they can lower your own production, or be confused with cortisol by some testing techniques.
• The time. A sample taken at 10am instead of 8am gives a lower figure. Night work shifts the whole rhythm.
• The stress of the blood test. Waiting, the needle, or a short night beforehand can push the level up in some people.
• An acute illness. Fever, infection, recent surgery, severe pain: cortisol rises, that is its job.
• Alcohol, severe depression, significant obesity. They can raise cortisol moderately, without any adrenal disease.

Always tell the laboratory and your doctor about your treatments, including those you do not think of as medicines: the pill, patches, nasal sprays, creams. If you use oestrogen-based contraception, your doctor may suggest a different test, or ask you to stop it a few weeks beforehand.

Home tests

Home cortisol test: what you are really buying.

Pharmacies, health shops and online retailers sell kits to measure your own cortisol. Most do not give an immediate result: you collect saliva, a drop of blood from your finger or dried urine, then send the sample to a laboratory. The result arrives a few days later, often with a graph of your day.

Our honest view: a home test can satisfy your curiosity, but it does not replace a proper check-up. If it comes back “abnormal”, you will have to repeat the test in a laboratory anyway. If it comes back “normal” while you feel unwell, it should not stop you seeing a doctor. Either way, your doctor holds the key.

Interpreting a result

High or low cortisol: when it is normal, when to worry.

Here is how doctors reason, greatly simplified. This table does not replace your doctor's interpretation, which will take your history and treatments into account.

A single result with no symptoms rarely leads to a diagnosis. Doctors almost always confirm with a second test.

To put words to the symptoms of excess cortisol and what can keep it going, our article high cortisol: symptoms and solutions covers the subject. Low cortisol will have an article of its own.

What a test cannot tell you

Your stress does not fit into a number.

This is probably the most important point in this article. Many people want to test their cortisol because they feel exhausted and tense, and they sleep badly. That is understandable: we would like proof, a number that explains everything. Cortisol is not that number.

In most stressed or tired people, cortisol stays within the normal range. Chronic stress can change the shape of the curve over the day, but these differences show up as averages across groups of people, not reliably in one individual. The idea of “adrenal fatigue”, very widespread online, is recognised neither by endocrinology societies nor by the 2016 systematic review cited above.

If you have felt at the end of your tether for weeks, the right starting point is a medical appointment, not a kit. Fatigue, sleep, mood, workload, deficiencies: your doctor can explore many more avenues. Our guide persistent fatigue: what to do helps you prepare for that appointment.

Preparing for your test

Three rules for a result that actually means something.

If your doctor prescribes a cortisol test, a few simple precautions make the result much more reliable. They apply to the laboratory as well as to a saliva sample taken at home.

For the 24-hour urine collection, you discard the first urine of the morning, then collect all urine up to and including the first of the next morning, keeping the container cool. A missed collection skews the total: it is better to start again on another day.

When to see a doctor

The signs that call for prompt medical advice.

Cortisol disorders are rare, but they do exist, and they can be treated. Some signs should prompt you to see a doctor, whether or not you have done a test.

Sudden fatigue with vomiting, abdominal pain and very low blood pressure, in someone with known adrenal insufficiency or who has just stopped corticosteroids, is an emergency: call 112.

After a normal result

Normal cortisol, but still on edge: where to start.

This is the most common situation. The test is reassuring, and yet the stress is there. The good news: the levers that matter most need no test. Regular sleep, daylight in the morning, moderate physical activity, caffeine kept for the morning, moments of real disconnection. Our article how to lower cortisol ranks them by level of evidence.

Some people add a plant-based routine to this foundation. Ashwagandha is the most studied: several trials have measured their participants' cortisol, with results and limitations that we detail in our article ashwagandha benefits and studies. It is in this spirit that we formulated Anti-Stress: ashwagandha standardised for withanolides, reishi, holy basil, schisandra and vitamin B6, which contributes to normal functioning of the nervous system and to the reduction of tiredness and fatigue.

• A supplement replaces neither sleep nor medical advice. It adds to a routine, it does not replace it.
• Repeating a cortisol test to “see if it works” makes no sense: the variation from one day to the next is greater than the expected effect.
• Judge instead by how you feel over the weeks: sleep, irritability, energy at the end of the day.

To find out more about the plant, see our ashwagandha page. And if your stress mainly affects your nights, our guide better sleep: 15 evening habits is a good place to start.

Sources

1. Nieman L. K. et al. (2008). The diagnosis of Cushing's syndrome: an Endocrine Society clinical practice guideline. Journal of Clinical Endocrinology & Metabolism, 93(5).
2. Bornstein S. R. et al. (2016). Diagnosis and treatment of primary adrenal insufficiency: an Endocrine Society clinical practice guideline. Journal of Clinical Endocrinology & Metabolism, 101(2).
3. Stalder T. et al. (2016). Assessment of the cortisol awakening response: expert consensus guidelines. Psychoneuroendocrinology, 63.
4. Cadegiani F. A., Kater C. E. (2016). Adrenal fatigue does not exist: a systematic review. BMC Endocrine Disorders, 16(1):48.
5. Stalder T. et al. (2017). Stress-related and basic determinants of hair cortisol in humans: a meta-analysis. Psychoneuroendocrinology, 77.

Keep reading

Further reading.

Cortisol is easier to understand than to measure. Discover our other guides on stress, or take a look at Anti-Stress.