A diurnal cortisol test shows the pattern of cortisol levels, a biomarker for stress, throughout the day. Abnormal changes in cortisol levels may be an indicator of an underlying mental or physical health issue.

A diurnal cortisol test measures cortisol levels in saliva throughout the day.

This test can help show whether cortisol levels follow a regular pattern and can help diagnose problems with adrenal function.

This article looks at what a diurnal cortisol test does, who may require one, how to prepare, the procedure, understanding the results, and when to see a doctor.

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The adrenal gland releases cortisol, a hormone that is a biomarker for stress. Abnormal changes in cortisol levels may help healthcare professionals diagnose certain health conditions.

The hypothalamic-pituitary-adrenal (HPA) axis is a mechanism involving the hypothalamus and pituitary gland in the brain, and the adrenal cortex, part of the adrenal gland.

During periods of stress, the HPA axis releases cortisol into the bloodstream. The body also releases cortisol at different points in the day to help regulate energy levels.

When the HPA axis is functioning normally, the release of cortisol follows a daily, or diurnal, cycle. Cortisol levels increase upon waking, which is the cortisol awakening response (CAR).

Cortisol levels typically double within the first 30 minutes of waking. As the day goes on, cortisol levels usually decrease. Changes in the CAR may link to a range of mental and physical conditions.

A diurnal cortisol test uses saliva samples to measure cortisol levels throughout the day. The test uses the results to make a diurnal curve — a graph that shows a person’s cortisol levels throughout the day.

Test results can help to show any abnormalities or irregularities in cortisol levels, which may indicate an underlying issue.

Who needs this test?

According to the Institute for Functional Medicine, changes to a regular diurnal cortisol pattern may indicate adrenal dysfunction.

People who may require a diurnal cortisol test may have symptoms of adrenal dysfunction, such as:

People can get at-home diurnal cortisol test kits and discuss their test results with a healthcare professional.

The person will take regular saliva samples throughout the day. The number of samples will depend on the test kit. For example, researchers in a 2022 study took samples from participants 6 times per day.

The results from the samples will then form a graph to show a diurnal cortisol curve.

A person will give samples by collecting a certain amount of saliva within a provided container. It may help to increase saliva production by drinking plenty of water or imagining sucking on a lemon.

People will then have to follow the shipping instructions to return the sample to the laboratory and wait for the results.

The specific preparation steps a person should take before this test may vary depending on the type. People can check packaging or speak with a healthcare professional first to ensure they do the right thing.

However, preparation may involve:

  • stopping certain medications before taking the test, under a doctor’s guidance or recommendation
  • not using prescription topical medication 24 hours before testing
  • not rinsing the mouth or brushing the teeth at least 30 minutes before each saliva collection
  • avoiding all food and drink for at least 30 minutes before each saliva collection
  • avoiding smoking for at least two hours before each saliva collection
  • avoiding black licorice for two weeks before testing

People should wash their hands thoroughly before testing and avoid touching the swab when collecting their saliva.

People who menstruate may also need to take the test during a certain part of their cycle.

According to a 2021 review, a typical diurnal curve peaks in the morning and decreases and levels out toward the end of the day. If a person is under stress, cortisol levels rise.

Cortisol production is lower during the first stage of sleep and rises during the second stage of sleep. The highest levels of cortisol occur after waking.

Levels gradually decrease throughout the day. The concentration of cortisol roughly halves at night compared to levels during the day. The lowest levels of cortisol are at around 4 a.m.

The results of a diurnal cortisol test may be specific to each individual test. Results that differ from the norm may be a sign of an underlying health issue. People can discuss the results with a doctor to understand what they mean.

Potential health implications

A 2017 systematic review found that flatter diurnal cortisol rhythms link to poorer outcomes for mental and physical health, including those relating to:

However, experts need further research to understand how the curve of the diurnal cortisol slope may link to certain health conditions.

Cost varies for different cortisol tests. Price may depend on the time it takes to receive results, among other factors.

Insurance providers may not cover at-home test kits, so it is best to contact the provider directly to ask.

According to the American Family Physician, certain lifestyle factors or medical conditions may affect how accurate the results of a cortisol test are.

Salivary cortisol tests, such as a diurnal cortisol test, may not be suitable for people with erratic sleep schedules or work shifts. Late-night salivary samples may not be accurate and can lead to misleading results.

If people have symptoms of chronic fatigue, chronic stress, or adrenal dysfunction, it is best to speak with a doctor.

A doctor can assess symptoms, take a medical history, and recommend any diagnostic testing a person may require.

A diurnal cortisol test measures cortisol levels throughout the day. People take regular saliva samples to send to a laboratory. The laboratory then produces a graph from the results to show a diurnal cortisol curve.

A typical diurnal cortisol curve peaks in the morning and then decreases gradually throughout the rest of the day. Abnormal changes in cortisol levels may be an indicator of a physical or mental health condition.

People can speak with a healthcare professional if they believe they need a diurnal cortisol test. A doctor can advise reputable brands and provide a complete diagnosis for any potential health conditions.