Hormones
Cortisol
Adrenal hormone measured in the morning to detect a serious deficiency or excess; not a measure of stress.
Everything about this testWhat it measures
Cortisol is made by the adrenal glands, controlled by ACTH from the pituitary gland. It regulates blood sugar, blood pressure, the immune system and the body's response to illness and tension. The value has a strong daily rhythm: high right after waking up, low around midnight. This analysis measures the total cortisol in the blood at a single moment, preferably between 8 and 10 in the morning.
- Adrenal insufficiency (Addison's disease, or failure due to the pituitary gland): a serious shortage of cortisol
- Suppression of the body's own cortisol production after long-term use of corticosteroids (prednisone, dexamethasone, including inhaled and skin products)
- First sign of Cushing's syndrome (too much cortisol), although other tests are better for this
High
A raised morning cortisol is usually not a disease. Tension around the blood draw, poor sleep, a night shift, heavy exercise, illness, fever, pregnancy, overweight, alcohol and the contraceptive pill (which raises the binding protein) all give higher values. Cushing's syndrome is rare and is not diagnosed with a single morning value; for that, the doctor uses a dexamethasone suppression test, late-evening saliva cortisol or cortisol in 24-hour urine. Symptoms that go with a cortisol level that is too high for a long time: weight gain on the trunk and in the face, thin skin with bruises, muscle weakness, high blood pressure and high blood sugar.
Low
A low morning cortisol may point to a deficiency caused by the adrenal glands themselves (Addison's disease) or by reduced control from the pituitary gland, with symptoms such as severe tiredness, weight loss, low blood pressure, dizziness when standing up, nausea, salt craving and darker skin. However, the most common cause is the use of corticosteroids, including as an inhaler, skin cream or injection, which suppress the body's own production. A clearly low morning value makes a deficiency likely and a clearly normal value makes it unlikely; with values in between, further testing (ACTH, a stimulation test) is needed. A blood draw later in the day gives a lower value without anything being wrong. 'Adrenal fatigue' due to stress is not a medically recognized diagnosis and is not shown with this test.
Preparation
- Have your blood taken between 8.00 and 10.00, because cortisol drops during the day.
- Avoid stress and heavy exercise shortly before the sample is taken.
- Do you use corticosteroids (tablets, inhaler, nasal spray or ointment)? They lower cortisol. Do not stop them yourself and discuss the result with your doctor.
- Do you take biotin (vitamin B8, often in hair and nail supplements)? Stop at least 2 days before the sample is taken, or 4 days for a high dose.
If your result is abnormal
With a low morning value, the GP repeats the measurement early in the morning, asks about corticosteroid use and usually has ACTH, sodium and potassium measured; with a persistently suspicious result, referral to an internist-endocrinologist for a stimulation test follows. With a high value and symptoms of Cushing's, a dexamethasone suppression test or saliva or urine cortisol follows.
Reliability
A single morning value is mainly useful for making a serious deficiency likely or unlikely; a clearly low or clearly normal value is informative, the values in between are not. A single blood value says nothing about stress, burnout or 'adrenal fatigue': the cortisol of healthy people under a lot of tension is within the same range as that of relaxed people, and overstrain or burnout cannot be diagnosed with a blood test. For showing an excess (Cushing's), other tests are more sensitive than a morning cortisol.
Limitations
- Timing: the reference values apply to a blood draw in the morning, at the latest around 10 a.m. Later in the day, the value is lower without anything being wrong. With night shifts or jet lag, the daily rhythm is shifted.
- Corticosteroids in any form (tablets, inhaler, nasal spray, skin cream, injection) lower the body's own cortisol; prednisone can also interfere with the measurement. The contraceptive pill and pregnancy raise total cortisol through the binding protein.
- Tension around the blood draw, lack of sleep, heavy exercise, illness, fever and alcohol temporarily raise the value.
- Reference values differ between laboratories and measurement methods; a cut-off value from one source does not fit a result from another laboratory.
How common is this
A shortage of adrenal cortex hormone (Addison's disease) is rare: an estimated 40 to 115 per million inhabitants, twice as often in women, usually diagnosed between the ages of 30 and 45. Cushing's syndrome is even rarer, with around 150 to 200 patients in the Netherlands; a GP sees at most one in an entire career. Suppressed cortisol production due to corticosteroid use is much more common.
Who is this useful for
Useful with symptoms that fit a deficiency, such as persistent severe tiredness with weight loss, low blood pressure, nausea and darker skin, and in people who have used corticosteroids for a long time or are tapering them off. If too much cortisol (Cushing's) is suspected, other tests say more. Not useful for measuring stress, burnout or 'adrenal fatigue', or with tiredness without other symptoms: the result is then almost always normal or cannot be interpreted.
Downsides and risks
- A raised value due to tension or the pill can wrongly be read as 'too much stress' or as a sign of Cushing's and lead to unnecessary tests.
- A low value due to a blood draw later in the day or an inhaled steroid can cause unjustified worry about the adrenal glands.
Sources
- NVKC, allesovertesten.nl: Cortisol
- Huisartsenbrochure Bijnierziekten (Bijniervereniging NVACP, via NHG)
- NHG-Standaard Overspanning en burn-out
- Thuisarts.nl: Stress
- Thuisarts.nl: Overspannen
Always discuss an abnormal result with your GP. If a result is strongly abnormal, we try to reach you as soon as possible. Read your result yourself as well and contact your GP if in doubt. A test does not make a diagnosis. Read more about risks and results