What is a cortisol blood test?

Cortisol mobilizes our biological resources to repair and protect the body during times of stress – here we explain why testing cortisol levels is important as we age.

Cortisol is released by the adrenal glands and plays an important role in metabolizing carbohydrates, proteins and lipids.

It is also a key stress-response hormone. However, as we age, our bodies continue to produce higher levels of cortisol for longer, which means that stress becomes even more damaging.

Testing cortisol levels involves a blood test (or saliva or urine test) that measures serum cortisol (hydrocortisone) and can diagnose conditions such as Cushing’s syndrome that are associated with too much cortisol.

Higher cortisol levels can also contribute to many other health conditions, including hypertension (high blood pressure), heart disease, high blood sugar levels (and diabetes), osteoporosis, obesity and Alzheimer’s disease.

Cortisol levels

Generally, cortisol levels are at their highest upon waking and at their lowest at bedtime (although with shift workers this pattern can change).

Normal morning ranges are 6-23 micrograms per deciliter (ug/dL). A higher level of cortisol in the morning, or a level that does not drop during the afternoon or evening, means there is probably an overproduction of cortisol.

Testing cortisol levels 

A doctor or nurse will take a blood sample from your arm usually around 8am or 4pm.

Those taking certain medications such as estrogen may need to briefly stop taking it for the test, as it may affect results. You may also need to fast the night before.


With health insurance, it can be free, or up to 50% cost with co-insurance. Those without insurance may pay a minimum of around $50 and as much as $150 or more, depending on how frequently they require the blood test.

When and how often?

There are no set guidelines as such for testing cortisol levels, although those who suffer specific conditions such as Addison’s or Cushing’s will often undergo regular cortisol testing.


Many factors can affect a cortisol blood test, including emotional stress, physical stress, illness, pregnancy and some medications.

Because the blood test is so sensitive to stress, you may need to provide a number of samples, or the doctor may use other cortisol tests, such as those requiring saliva or urine samples, to help make an accurate assessment about your cortisol levels.

Doctors may also need to carry out additional tests, such as a dexamethasone suppression test, which assesses how the adrenal glands respond to the hormone ACTH (which regulates cortisol).

Researchers have also shown that professionals should exercise caution when making conclusions about adrenal gland function based on testing cortisol levels with a single random test.



Last reviewed 9/Jul/2017

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