Cortisol has many functions. It helps the body use sugar (glucose) and
fat for energy (metabolism), and it helps the body manage stress.
Cortisol levels can be affected by many conditions, such as physical or
emotional stress, strenuous activity, infection, or injury.
Normally, cortisol levels rise during the early morning hours and are
highest about 7 a.m. They drop very low in the evening and during the early
phase of sleep. But if you sleep during the day and are up at night, this
pattern may be reversed. If you do not have this daily change (diurnal rhythm)
in cortisol levels, you may have overactive adrenal glands. This condition is
The timing of the cortisol test is very important because of the way cortisol levels vary throughout a day. If your doctor thinks you might make too much cortisol, the test will probably be done late in the day. If your doctor thinks you may not be making enough, a test is usually done in the morning.
Why It Is Done
cortisol test is done to find problems of the
pituitary gland or adrenal glands, such as making too much or too little
How To Prepare
You may be asked to avoid strenuous
physical activity the day before a cortisol test. You may also be asked to lie
down and relax for 30 minutes before the blood test.
medicines may change the results of this test. Some medicines, such as
steroids, can affect cortisol levels for some time even after you stop taking
the medicine. Be sure to tell your doctor about all the
nonprescription and prescription medicines you
Talk to your doctor about any concerns you have regarding
the need for the test, its risks, how it will be done, or what the results will
mean. To help you understand the importance of this test, fill out the
medical test information form(What is a PDF document?).
How It Is Done
The health professional drawing your
Wrap an elastic band around your upper arm to
stop the flow of blood. This makes the veins below the band larger so it is
easier to put a needle into the vein.
Clean the needle site with
Put the needle into the vein. More than one needle stick
may be needed.
Attach a tube to the needle to fill it with
Remove the band from your arm when enough blood is
Put a gauze pad or cotton ball over the needle site as
the needle is removed.
Put pressure to the site and then a
How It Feels
The blood sample is taken from a vein in
your arm. An elastic band is wrapped around your upper arm. It may feel tight.
You may feel nothing at all from the needle, or you may feel a quick sting or
There is very little chance of a problem from
having a blood sample taken from a vein.
You may get a small bruise at the site. You can
lower the chance of bruising by keeping pressure on the site for several
In rare cases, the vein may become swollen after the blood
sample is taken. This problem is called phlebitis. A warm compress can be used
several times a day to treat this.
Ongoing bleeding can be a
problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and
other blood-thinning medicines can make bleeding more likely. If you have
bleeding or clotting problems, or if you take blood-thinning medicine, tell
your doctor before your blood sample is taken.
A cortisol test is done to measure the
level of the
hormone cortisol in the blood.
The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.
A high level of cortisol in the blood can
Cushing's syndrome, a disorder that can be caused by
overactive adrenal glands, an adrenal gland tumor, some types of
cancer, or long-term use of
radioactive scan within 1 week of a cortisol test.
What To Think About
A 24-hour urine test is used more often than a
cortisol blood test to diagnose Cushing's syndrome. To learn more about
cortisol in urine, see the topic
Cortisol in Urine.
Other tests that can
help determine if the pituitary gland or adrenal glands are functioning
properly include the adrenocorticotropic hormone (ACTH) stimulation test and
dexamethasone suppression tests. The ACTH stimulation test may be done when
Addison's disease is suspected.
How this information was developed to help you make better health decisions.