Cortisol is a steroid hormone produced by the adrenal glands in response to a pituitary hormone called adrenocorticotropic hormone (ACTH). Diseases of the adrenal glands and diseases of the pituitary gland are among the causes of abnormal cortisol levels. For this reason, ACTH and cortisol are often evaluated together.
Cortisol plays a role in the metabolism of carbohydrates, fats, and proteins. In addition, it mobilizes stored sugar in the liver to produce energy, and also helps to regulate blood pressure and the immune system. Cortisol is often released in response to stress.
The 24-Hour Cortisol Cycle
Cortisol levels normally rise and fall throughout the day. This is called a diurnal variation. Cortisol levels usually reach their peak around 6 a.m. to 8 a.m. They fall during the day to reach a minimum at around midnight. These levels repeat on a 24-hour cycle.
However, the timing of cortisol levels in a 24-hour cycle may be different for people who work irregular shifts or sleep at unusual times of the day.
Why a Cortisol Test Is Ordered
Cortisol level tests may be performed when a person has symptoms of high or low cortisol levels.
Symptoms of High Cortisol Levels
Cushing’s syndrome is a collection of symptoms associated with high cortisol levels. The most common of these symptoms are:
- high blood pressure
- high blood sugar
- obesity in the torso
- fragile skin
Women may have irregular periods and excess facial and chest hair. Children may be obese or short or have delayed physical development.
Symptoms of Low Cortisol Levels
The symptoms of low cortisol levels are often vague and nonspecific. Symptoms may emerge slowly and only appear during stressful times at first. After that, the intensity of symptoms may increase over a period of months. Potential symptoms include:
- weight loss
- dizziness or fainting
- muscle weakness
- abdominal pain
- decreased body hair
- diarrhea or constipation
An adrenal crisis may cause a sudden and life-threatening drop in cortisol levels. Symptoms include:
- low blood pressure
- loss of consciousness
- dehydration resulting from vomiting and diarrhea
- sudden onset of severe pain in the lower back, abdomen, or legs
Types of Cortisol Level Tests
A 24-hour cortisol urine test measures the total amount of free cortisol excreted into the urine in a 24-hour period. By contrast, blood tests or saliva tests only measure cortisol levels at a particular time in the diurnal cycle.
However, where the urine test only measures the presence of free cortisol, blood tests measure both free cortisol and protein-bound cortisol. The level of blood cortisol is helpful to doctors in diagnosing Addison’s disease and adrenal insufficiency, because these are both conditions in which the adrenal gland does not work correctly.
Some people find blood tests to be stressful, which can affect the test results. The body often releases cortisol in response to stress. Sometimes doctors will substitute saliva tests for blood tests for this reason.
In certain cases, a doctor may order both urine and blood tests to occur at different times of the day. Combining these tests can help the doctor determine how cortisol levels vary throughout the day and accumulate a broader set of data regarding potential conditions affecting cortisol levels.
Taking a Cortisol Urine Test
A cortisol urine test is painless and only involves ordinary urination. Cortisol is measured in a urinary sample collected over a 24-hour period.
The collection procedure is as follows:
- On day 1, urinate into the toilet upon arising and flush this first sample away.
- For the rest of the day, collect all urine in a special container and store it in a cool place.
- On day 2, urinate into the special container upon rising.
- Return the container to the lab as soon as possible.
Cortisol Urine Tests for Infants
Parents of infants will need to wash the area around the baby’s urethra and attach a collection bag. For a boy, place the bag over his penis. For a girl, place the bag over her labia. Then put the baby’s diaper on over the bag.
Collect samples over the same 24-hour period as for adults. It will be necessary to check the bag throughout the collection period and change the bag each time the baby has urinated. Pour each sample into a collection container, and keep this container in a cool place. Return the container to the lab as soon as possible.
Preparing for the Cortisol Urine Test
Your healthcare provider may instruct you to stop taking medications that could interfere with the accuracy of the cortisol urine test. These medications include:
- tricyclic antidepressants
Parents of infants taking the test may wish to have extra collection bags available in case an active baby dislodges a bag.
A normal range for cortisol is 10-100 micrograms per 24 hours (mcg/24h). However, normal ranges may vary slightly between different labs.
Abnormal results could be caused by a number of conditions.
Cushing’s syndrome is a collection of symptoms caused by high cortisol levels. It may be caused by:
- overproduction of cortisol due to a tumor in the adrenal gland
- overproduction of ACTH due to a tumor in the pituitary gland (Cushing’s disease, which is a form of Cushing’s syndrome)
- overproduction of ACTH due to a tumor outside of the pituitary gland
- ingestion of substances that raise cortisol levels
- severe depression or stress
Low cortisol levels may be caused by insufficient production of cortisol in the adrenal glands or insufficient production of ACTH in the pituitary gland. If the adrenal glands don’t produce enough cortisol, the condition is called Addison’s disease or primary adrenal insufficiency. Dysfunction of the pituitary gland causes secondary adrenal insufficiency.
Further testing may be necessary to diagnose any of these conditions.