Cortisol levels are measured with timed blood, saliva, or 24-hour urine tests that track your daily rhythm and point to the right next step.
What Cortisol Does And Why Testing Varies
Cortisol helps you wake, steady blood sugar, and handle physical stressors. It rises before dawn, peaks in the morning, then drifts lower through the day. That swing is the reason timing matters so much. A random number tells little. The right test, at the right hour, answers a specific question: too high, too low, or just not following the expected curve. Picking the method is less about chasing a single “perfect” value and more about matching your situation to a proven approach.
Think of testing as a set of tools. Each one gives a different snapshot. A morning blood draw checks the peak. A late-night saliva sample checks the trough. A 24-hour urine jug captures the whole day. A dexamethasone check shows whether cortisol suppresses when it should. An ACTH stimulation checks whether the adrenal glands can mount a rise on cue. The sections below explain when each tool fits best and how to do it without avoidable errors.
Cortisol Tests At A Glance
| Test | What It Shows | When It’s Commonly Used |
|---|---|---|
| Morning Serum Cortisol | Peak level around 7–9 a.m. | Screening for low cortisol; triage before ACTH stimulation |
| Late-Night Salivary Cortisol | Trough level near bedtime | Screening for high cortisol patterns linked to Cushing syndrome |
| 24-Hour Urine Free Cortisol | Total cortisol across a full day | Confirming sustained excess production |
| 1-mg Dexamethasone Suppression | Ability of cortisol to suppress after a low steroid dose | Rule-in screening for suspected cortisol excess |
| ACTH (Cosyntropin) Stimulation | Adrenal rise after a standard ACTH dose | Confirming or ruling out adrenal insufficiency |
How To Find Out Your Cortisol Levels Safely And Accurately
Start by stating your goal. Are you chasing symptoms that match high cortisol, such as easy bruising, facial rounding, or hard-to-control blood pressure? Or are you dealing with lightheadedness, salt craving, fatigue with weight loss, or darkening of skin folds that suggest low cortisol? That initial picture guides the first test. If the picture points to possible excess, late-night saliva or a 24-hour urine jug is the usual start. If the picture points to low levels, a timed morning blood draw followed by ACTH stimulation is the usual path.
Pick the right clock. Sleep at regular hours for two or three nights before sampling. Shift work changes the “night” window, so match the late-night sample to your own bedtime, not the wall clock. Skip hard exercise the evening before a late-night sample. Skip a nap near the sampling window. Keep caffeine moderate on collection day. List all medicines and supplements, including oral estrogens, prednisone, hydrocortisone, inhalers, nasal sprays, and licorice products. These can tilt results and should be reviewed during ordering and interpretation.
At-Home Saliva Collection
Use the kit your lab provides. Collect right at your usual bedtime, not after midnight snacks or brushing. Rinse with water ten minutes before. No food, gum, smoke, or toothpaste during that window. Fill the tube with drool, not sputum. Cap it tight and follow the storage note on the kit. Many kits go in the fridge; some go in the freezer. Send the sample the next morning. If sleep was off that night, repeat on a better night. Two separate late-night samples give a cleaner read than one.
24-Hour Urine Collection
Pick a normal day. On wake-up, empty your bladder into the toilet and note that time as the start. After that, collect every drop for the next 24 hours in the jug from the lab. Keep the jug cool. At the same time next day, empty your bladder into the jug and mark the stop. Label start and stop times. If you miss a void, start a new day. Pairing two jugs on different days helps catch day-to-day swings. Bring all jugs back together so the lab can average or review both.
Morning Blood Draw
Sleep at regular hours for two nights. Go to the lab early, ideally 7–9 a.m. Sit for fifteen minutes before the draw. Skip biotin the day before unless your doctor says otherwise. Bring your full medicine list. If you take replacement steroids, ask about timing the dose after the draw to avoid a false bump. If the morning number looks borderline, an ACTH stimulation on a separate day settles the question far better than repeating random morning checks.
When A Single Number Misleads
Cortisol pulses across the day. A morning value can look fine while late-night levels run high. A lone late-night value can drift upward after a stressful day. Illness, surgery, pain, or a hard workout can spike levels. Oral estrogens raise cortisol-binding globulin, which lifts total serum cortisol even when free cortisol stays the same. That is why saliva and urine free cortisol are so handy in the high-cortisol workup, and why ACTH stimulation is favored in the low-cortisol workup. Match the test to the question, then confirm with a second method when the picture is mixed.
Common Scenarios And First Tests
Possible High Cortisol (Cushing Pattern)
Start with two late-night salivary cortisol samples on different nights, or two 24-hour urine free cortisol collections, or a 1-mg dexamethasone suppression check ordered and timed by your clinician. The Endocrine Society screening guidance for Cushing syndrome backs this strategy and lists the tests with the strongest signal for early screening. If both screening checks are normal, true sustained excess is unlikely. If one or both are high or fail to suppress, targeted imaging and hormone checks follow, guided by an endocrinologist.
Possible Low Cortisol (Adrenal Insufficiency)
Begin with a timed morning serum cortisol. If the number falls in a gray band, move to ACTH stimulation, which is the standard way to prove adrenal reserve. The NIDDK page on the ACTH stimulation test explains the steps in plain language. A normal rise argues against adrenal insufficiency. A flat or blunted rise points to primary adrenal disease or secondary suppression, which your clinician can sort out with ACTH, renin, aldosterone, and medication history.
Prep Steps That Prevent Do-Overs
Hold late nights and travel the week of testing if you can. Keep meals steady on collection day. Skip tough training the evening before late-night saliva and during a urine collection window. Avoid minty toothpaste or mouthwash right before saliva. Note sleep times, dose times, and any near-fainting spells on the requisition or a note you hand to the phlebotomist. These small details save repeat visits and help the lab read your number in the right light.
Medication And Health Factors You Should Flag
Tell your clinician about steroid pills, creams, eye drops, and inhalers. Ask about oral estrogens and pregnancy, which raise cortisol-binding proteins and can nudge total serum values upward. Note antidepressants, anti-seizure drugs, and HIV medicines that change dexamethasone metabolism. Mention licorice, which can mimic cortisol at the receptor. Flag kidney disease when ordering a urine study and sleep apnea when ordering late-night saliva. None of these are rare. Calling them out early makes results easier to trust.
What Can Skew A Cortisol Test
| Factor | How It Affects | What To Do |
|---|---|---|
| Shift Work | Shifts the “late-night” window | Match saliva timing to your real bedtime |
| Oral Estrogens | Raise total serum cortisol | Favor saliva or urine for excess screens |
| Glucocorticoid Use | Alters all assays | List all forms; time doses per order |
| Acute Illness Or Pain | Temporary spikes | Delay elective testing until stable |
| Hard Evening Workouts | Raises late-night values | Skip or train earlier on saliva nights |
| Licorice Products | Raises cortisol activity | Pause after checking with your clinician |
| Kidney Disease | Alters urine results | Use serum or saliva methods |
| Assay Differences | Cutoffs vary by method | Interpret with lab-specific ranges |
Understanding Reference Ranges
Each lab prints its own range because methods differ. Two labs can report different numbers on the same person. That is normal. Focus less on a single cutoff and more on whether the number fits the time of day and the test’s goal. A low morning serum value raises suspicion for adrenal insufficiency, but the ACTH stimulation confirms the truth. A high late-night saliva or high urine free cortisol points toward excess output, but repeating on a separate day guards against a one-off spike.
Reading Results Without Overreach
Think in patterns. Morning low with a flat ACTH stimulation suggests impaired adrenal reserve. Late-night highs on two saliva kits, or repeated high urine totals, point toward sustained excess. A failed dexamethasone suppression adds weight. Normal paired screens make true disease less likely, even when a single test looked off. If anything conflicts, retest under cleaner conditions. Bring logs of sleep, shift schedule, and dose timing to your visit so your clinician sees the full picture.
Home Versus Lab: Picking The Setting
Saliva kits are quiet, cheap, and easy to repeat. They shine for late-night checks and for people with white-coat spikes. Urine jugs work well if you can plan a normal day and keep the jug cool. Blood tests are best when supervised timing or downstream hormone panels are needed. Many workups mix methods: saliva for screening, urine to confirm, then targeted blood tests to sort causes. That blend cuts false alarms and limits extra imaging.
Cost, Access, And Practical Tips
Insurance rules vary. Many plans cover screening when ordered with clear symptoms. If paying cash, ask the lab to quote saliva kit, urine jug, and ACTH stimulation fees in advance. Pick a single lab group for the whole workup so ranges and methods match. When mailing saliva, track the package. When carrying a urine jug, use the lab’s cooler bag and keep it out of heat. Snap photos of labels and times as a backup. Small steps keep the chain tidy.
When To See An Endocrinologist
Book a visit if screening is abnormal, if you use chronic steroid medicines, if you are pregnant with confusing numbers, or if you have a history of pituitary, adrenal, or thyroid disease. Bring copies of all results, the medicine list, and your symptom timeline. Many clinics prefer two screening tests for suspected excess before imaging. For suspected low cortisol, ACTH stimulation is the pivot test, and specialty care speeds the rest of the workup.
Key Takeaways You Can Act On Today
- Match the test to the question: morning serum and ACTH stimulation for low suspicion; late-night saliva, urine free cortisol, or dexamethasone suppression for high suspicion.
- Time samples to your own sleep schedule, not a rigid clock, and repeat abnormal screens on a second day.
- Flag medicines, oral estrogens, licorice, tough workouts, and illness before you collect.
- Stick with one lab when possible and read numbers against that lab’s method.
Sources And Method Notes
This guide aligns with Endocrine Society screening paths for suspected cortisol excess and the NIDDK description of ACTH stimulation for low cortisol states. It favors repeat screening before imaging and uses lab-specific ranges rather than fixed universal cutoffs. That approach keeps false alarms low and reduces repeat visits.