What a cortisol test measures
A cortisol test measures the level of cortisol in a sample of your blood, saliva, or urine. Cortisol is a hormone made by your adrenal glands, the two small glands that sit on top of your kidneys, and it affects nearly every tissue in the body. According to MedlinePlus, cortisol helps you respond to stress, regulates blood glucose and metabolism, and helps control blood pressure and the body's response to infection.
Cortisol production runs on a feedback loop. Your pituitary gland releases a signal called ACTH (adrenocorticotropic hormone), which tells the adrenal glands how much cortisol to make. A cortisol test captures how that system is behaving, either at a single moment or across a full day, depending on the sample used.
Because cortisol touches stress, sleep, blood sugar, and metabolism, it often appears in broader health panels rather than as an isolated number. Different Health, for example, includes a morning cortisol reading in the 125-plus biomarker blood panel that comes with its DH360+ assessment, so the result is read alongside metabolic and hormonal markers rather than in isolation.
The main types of cortisol test
There is no single cortisol test. The right sample depends on what a clinician is trying to answer, and many evaluations use more than one. A cortisol blood test measures both protein-bound and free cortisol at the moment of the draw; saliva and urine tests measure the free, biologically active portion. Two additional tests, the dexamethasone suppression test and the ACTH stimulation test, are used to work out the cause once a first result looks abnormal.
| Test | Sample & timing | Typically used to look for |
|---|---|---|
| Blood (serum) cortisol | Blood draw, usually early morning | A first read on high or low cortisol; often the starting point |
| Late-night salivary cortisol | Saliva, collected at home late at night | Excess cortisol, when the level should be at its lowest |
| 24-hour urine free cortisol | All urine collected over a full day | Total daily cortisol output, to screen for excess |
| Dexamethasone suppression test | Blood, after taking dexamethasone the night before | Whether cortisol suppresses normally, a screen for excess |
| ACTH stimulation test | Blood, before and after a synthetic ACTH injection | Whether the adrenal glands respond, a check for low cortisol |
Common cortisol tests and what each is used for. Source: Cleveland Clinic; Endocrine Society.
For suspected cortisol excess, the Endocrine Society recommends starting with one of three screening tests with high diagnostic accuracy: a 24-hour urine free cortisol, a late-night salivary cortisol, or a 1-milligram overnight dexamethasone suppression test. Which one is chosen depends on the person and the situation, and an abnormal result on any of them points toward more evaluation, not a diagnosis.
Normal cortisol levels and how to read them
Normal cortisol levels are not a single number, because the hormone follows a daily rhythm. Levels are highest in the early morning and decline through the day, reaching their lowest point around midnight. That is why the time on your lab slip matters as much as the value itself.
| Time of sample | Typical range (mcg/dL) |
|---|---|
| 6 a.m. to 8 a.m. | 10 to 20 |
| Around 4 p.m. | 3 to 10 |
Typical blood cortisol ranges by time of day. Ranges vary by lab, method, and individual. Source: Cleveland Clinic.
Cleveland Clinic notes that these ranges can differ from lab to lab and from person to person, so your own report should be read against that lab's reference values and your collection time. A morning cortisol reading that looks high for the afternoon may be entirely normal for 7 a.m. This is one reason a result is most useful when a clinician interprets it rather than a chart alone. Part of what Different Health does after bloodwork is exactly that: an in-house MD reviews the panel and explains what each marker means for you before it turns into any plan.
This article is educational and is not a substitute for personal medical advice. If your results fall outside a lab's range, that is a conversation to have with your own clinician, who can see your full history.
What high or low results can mean
A cortisol level outside the expected range can point in two broad directions, though neither is a diagnosis on its own.
Higher-than-expected cortisol
Per Cleveland Clinic, high readings can come from taking corticosteroid medications, a pituitary tumor producing extra ACTH, an adrenal tumor making too much cortisol, or, less commonly, a tumor elsewhere in the body. Sustained excess cortisol from within the body is called Cushing syndrome. Everyday factors such as stress and illness can also nudge a reading upward, which is why a single high value is not treated as Cushing syndrome without confirmation.
Lower-than-expected cortisol
Low readings can reflect underactive or damaged adrenal glands, or a pituitary gland that is not sending enough ACTH. When the adrenal glands cannot make enough cortisol, the condition is called Addison's disease. Because cortisol is naturally highest in the morning, a low morning value is often the trigger for a follow-up ACTH stimulation test to see whether the adrenal glands respond.
No single cortisol test is treated as definitive. For suspected cortisol excess, the Endocrine Society advises screening with a high-accuracy test and confirming abnormal results before moving toward a diagnosis.
— Endocrine Society, Diagnosis of Cushing's Syndrome clinical practice guideline
What affects your result, and how to prepare
Cortisol is sensitive, which is a strength and a complication. The same responsiveness that makes it a useful stress marker also means a reading can move for reasons that have nothing to do with disease. Cleveland Clinic lists stress, physical activity, serious illness, hot and cold temperatures, certain medications, and when you sleep as factors that can shift a result. Steroid medications, estrogen, and oral contraceptives are common examples that can alter values.
Preparation depends on the sample:
| Test type | What to do beforehand |
|---|---|
| Blood | Rest before the draw so stress does not raise the reading; ask whether timing is set for morning. Fasting is not usually required. |
| Saliva | Do not eat, drink, brush, floss, smoke, or vape for 30 minutes before collecting; sample at the time specified (often late night). |
| 24-hour urine | Collect every urination over a full day into the provided container, keep it cold, and note exact start and end times. |
How preparation differs by test type. Follow the specific instructions your provider gives you. Source: Cleveland Clinic.
Night-shift work and irregular sleep can flip the usual pattern, so tell whoever orders the test about your schedule. If you want to lower a cortisol level that stress or lifestyle is driving up, that is a separate topic from testing; the practical habits are covered in our guide to lowering cortisol.
Reading cortisol in context
A cortisol value is most meaningful next to the rest of your picture: sleep quality, stress, blood sugar, and other hormones all interact with it. On its own, one number rarely tells the whole story, which is why clinicians repeat testing and combine samples. It is also why cortisol is more useful inside a broader assessment than as a one-off.
This is the layer Different Health focuses on. The DH360+ blood panel is processed outside the lab and reviewed by an in-house MD, then combined with the rest of your results, including the metabolic, stress, and sleep-related measures gathered during the assessment. A team of MDs and PhDs turns that combined view into a personalized plan, with coaching and nutrition guidance, rather than handing you a lab value and leaving you to interpret it.
Key takeaways
- Cortisol test: measures cortisol in blood, saliva, or urine to check for too much or too little.
- Timing matters: cortisol is highest in the early morning and lowest around midnight, so results are read against collection time.
- Normal ranges vary: Cleveland Clinic lists roughly 10 to 20 mcg/dL at 6 to 8 a.m. and 3 to 10 mcg/dL near 4 p.m., but ranges differ by lab.
- No single test is definitive: the Endocrine Society recommends confirming abnormal screens with further testing.
- Many things move it: stress, illness, exercise, sleep timing, and some medications can all shift a reading.
- Context wins: a cortisol value means the most when read alongside your other markers and history.
Frequently asked questions
What does a cortisol test measure?
A cortisol test measures the amount of cortisol, a hormone made by your adrenal glands, in your blood, saliva, or urine. It checks whether your body is producing too much or too little, which can point to conditions affecting the adrenal or pituitary glands.
What are normal cortisol levels?
For most blood tests, Cleveland Clinic lists a typical range of about 10 to 20 mcg/dL between 6 and 8 a.m. and about 3 to 10 mcg/dL around 4 p.m., because cortisol falls through the day. Ranges vary by lab and by the time the sample is taken, so results are always read against your collection time.
What is the best time to test cortisol?
It depends on what is being checked. If low cortisol is the concern, a morning blood draw is common, since levels are naturally highest then. If high cortisol is suspected, a late-night salivary sample is often used, because that is when levels should be at their lowest.
Do you need to fast for a cortisol test?
Fasting is not usually required for a cortisol blood test, but you should follow your provider's instructions. For a salivary test, Cleveland Clinic advises not eating, drinking, brushing, flossing, smoking, or vaping for 30 minutes beforehand. Resting before the test also helps, since stress can raise the reading.
What causes high cortisol levels?
High readings can come from corticosteroid medications, a pituitary or adrenal tumor, or a tumor elsewhere in the body. Everyday factors such as stress, physical activity, and illness can also raise cortisol, which is why an abnormal result is confirmed with further testing rather than treated on its own.
Can stress raise your cortisol test result?
Yes. Cortisol is the body's main stress hormone, and stress, physical activity, serious illness, temperature, sleep timing, and certain medications can all shift a single reading. This is why providers rest you before testing and interpret results in the context of your symptoms and history.
References
- Cleveland Clinic. Cortisol Test: What It Is, Purpose, Types & Results.
- MedlinePlus (U.S. National Library of Medicine). Cortisol Test.
- Endocrine Society. Diagnosis of Cushing's Syndrome: Clinical Practice Guideline Resources.
- Thau L, Gandhi J, Sharma S. Physiology, Cortisol. StatPearls (NIH/NCBI Bookshelf).