Cortisol is measured through blood, saliva, or urine, and each method captures something different about how your body produces this stress hormone. A standard morning blood draw is the most common starting point, with normal levels falling between 10 and 20 micrograms per deciliter (mcg/dL) when taken between 6 and 8 a.m. Which test your doctor orders depends on what they’re looking for, whether that’s a snapshot of your cortisol right now or a picture of your total output over an entire day.
Why Timing Matters More Than the Test Itself
Cortisol follows a predictable daily rhythm that directly affects how results are interpreted. Levels are highest when you wake up, then surge another 50 to 60 percent in the 30 to 40 minutes after waking. From there, they drop quickly over the next few hours and continue declining more slowly until they bottom out around bedtime. A reading of 15 mcg/dL at 7 a.m. is perfectly normal. That same number at 4 p.m., when the expected range is only 3 to 10 mcg/dL, would raise a red flag.
This rhythm is exactly what doctors exploit when screening for problems. In Cushing syndrome, where the body produces too much cortisol, that natural evening dip disappears. Cortisol stays elevated around the clock. That’s why a late-night saliva test is one of the earliest and most sensitive ways to catch it. In Addison’s disease, where cortisol is too low, a morning blood draw is most useful because that’s when levels should be at their peak.
Blood Cortisol Test
A blood test, also called a serum cortisol test, is the most straightforward method. A technician draws blood from a vein, typically between 6 and 8 a.m. to catch the morning peak. Your doctor may also order an afternoon draw around 4 p.m. to see how steeply your levels drop, or they may ask for both on the same day. Normal morning values generally range from 10 to 20 mcg/dL, while afternoon values run between 3 and 10 mcg/dL.
Because cortisol spikes in response to physical and emotional stress, you may be asked to rest quietly before the draw. Exercise, anxiety, and even the stress of the needle itself can temporarily push your numbers up. Your doctor may also ask you to fast beforehand, though this varies by practice.
Several medications can throw off blood cortisol results. Birth control pills and other estrogen-containing medications are among the most common culprits because they increase the proteins that bind to cortisol in your blood, artificially inflating the reading. Corticosteroid medications like prednisone, anti-seizure drugs, certain antibiotics, and diuretics can also interfere. Your doctor will typically ask you to pause these before testing, but don’t stop any medication on your own without checking first.
Salivary Cortisol Test
Saliva testing is painless, can be done at home, and is especially useful for detecting abnormally high nighttime cortisol. The standard protocol calls for collecting a sample between 11 p.m. and midnight, right when cortisol should be at its lowest point. You place a small cotton swab (called a Salivette) under your tongue or between your cheek and gum, let it soak up saliva for a few minutes, then seal it in a tube.
Preparation matters. For at least 60 minutes before collection, you should not eat, drink anything, brush your teeth, or take any oral medication. About 10 minutes before collecting the actual sample, rinse your mouth thoroughly with water. This prevents food residue, blood from your gums, or other substances from contaminating the result. Even topical creams containing hydrocortisone can affect salivary cortisol readings, so mention all medications, including things you apply to your skin, to your provider.
Doctors often order two late-night saliva collections on separate nights. A single elevated reading could reflect a bad night or a collection error, so repeating the test increases confidence in the result. Subtle increases in midnight salivary cortisol are considered one of the earliest detectable signs of Cushing syndrome.
24-Hour Urine Cortisol Test
While blood and saliva give you a snapshot, a 24-hour urine collection captures your total cortisol output over an entire day. This is called urinary free cortisol (UFC), and it measures only the “free” cortisol circulating in your body, the active form that isn’t bound to proteins. That distinction matters because it sidesteps the problem of estrogen and birth control pills falsely raising results, which makes urine testing a good complement to blood work.
The process takes a full day. On the morning you start, you urinate into the toilet as usual when you wake up, then collect every subsequent urine sample in a special container for the next 24 hours. On the following morning, you add your first urination of the day to the container, cap it, label it with your name and the date, and return it to the lab. The container needs to stay cool (a refrigerator works) during the collection period. Missing even one sample during those 24 hours can make the results unreliable, so planning around a day when you’ll be home is practical advice.
Hair Cortisol Testing
A newer method measures cortisol that has been incorporated into hair as it grows. Since scalp hair grows at roughly 1 centimeter per month, a 1-cm segment cut close to the scalp reflects your average cortisol production over the past month. A 3-cm segment covers roughly three months, and testing can look back as far as six months, though cortisol concentrations in hair tend to degrade beyond that point.
This makes hair cortisol uniquely suited to studying chronic stress, something that blood, saliva, and urine tests simply cannot capture. A single blood draw tells you what’s happening right now. A 24-hour urine test covers one day. Hair cortisol covers weeks to months, giving researchers and clinicians a window into long-term stress exposure. It has been linked to chronic psychological stress, mental health conditions, and the cumulative physical toll of sustained stress over time.
Hair cortisol testing is primarily used in research settings rather than routine clinical practice. There is no standardized extraction technique yet, and results can vary between laboratories by 9 to 12 percent depending on the method used. Still, it fills a gap that no other cortisol test can address.
How to Prepare for Any Cortisol Test
The single most important thing you can do is give your doctor a complete list of everything you take, including prescription medications, supplements, and topical creams. Oral contraceptives, corticosteroids, anti-seizure drugs, and diuretics are the most common sources of inaccurate results, and your doctor may need to adjust or pause them before testing.
Beyond medications, keep these practical points in mind:
- Minimize stress before the test. Cortisol rises with physical and emotional stress, so avoid vigorous exercise and try to stay calm before a blood draw or saliva collection.
- Follow timing instructions precisely. A morning blood test drawn at 10 a.m. instead of 7 a.m. will produce a meaningfully different number. A saliva sample collected at 9 p.m. instead of 11 p.m. misses the point of the test entirely.
- Expect repeat testing. Because cortisol fluctuates so much throughout the day and from day to day, a single abnormal result rarely leads to a diagnosis. Most doctors will order at least two rounds of testing, sometimes using different methods, before drawing conclusions.
What Abnormal Results Can Mean
Cortisol testing is most commonly ordered to evaluate two conditions. Cushing syndrome, caused by prolonged excess cortisol, can produce weight gain concentrated in the face and midsection, thinning skin, easy bruising, and muscle weakness. Addison’s disease, caused by insufficient cortisol, leads to fatigue, darkening skin, low blood pressure, and salt cravings. Certain tumors, particularly in the pituitary or adrenal glands, can also drive cortisol levels abnormally high.
No single cortisol number definitively confirms or rules out these conditions. Diagnosis typically involves combining results from multiple test types. A doctor might start with a late-night salivary cortisol and a 24-hour urine collection, then follow up with a specialized suppression test that checks whether your cortisol responds normally to a synthetic hormone designed to lower it. For suspected adrenal insufficiency, a low morning blood cortisol is an important early clue, but stimulation testing is usually needed to confirm the diagnosis.