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Cortisol
The stress hormone of the adrenal glands — its level depends on the time of day, so the hour of the draw matters.
Other names: Hydrocortisone, serum cortisolSection: Hormones
Updated: August 29, 2026·MedProtect editorial team Reference information — not a diagnosis or a prescription
In shortFor a blood sample taken at 8 in the morning, normal values are 5–25 mcg/dL (138–690 nmol/L). Normal values depend on the time of day and the clinical context — a result from a stimulation or suppression test is expected to fall outside this range.
Reference ranges
Group
Reference range
Blood sample at 8 a.m.
5–25 mcg/dL (138–690 nmol/L)
Normal values depend on the time of day and the clinical context, and vary slightly among laboratories. Results from cosyntropin stimulation or dexamethasone suppression tests are expected to follow their own rules.
Check your value
Enter the number from your lab report — see how it compares with the typical range. Mind the units shown in the chosen row.
A rough comparison with a typical range, not a diagnosis. Reference ranges vary between laboratories — check the range on your own report and let a clinician interpret the result.
What this marker is
Cortisol is a hormone made by the adrenal glands, two small glands that sit on top of the kidneys. It plays a role in bone growth, blood pressure control, immune system function, the metabolism of fats, carbohydrates, and protein, nervous system function, and the stress response. Different diseases — Cushing syndrome and Addison disease among them — lead to too much or too little cortisol production, and measuring blood cortisol helps diagnose these conditions and evaluate how well the pituitary and adrenal glands are working.
The level follows a daily rhythm: highest in the early morning, lowest around midnight. That is why a normal range is tied to the hour of the blood draw — 5–25 mcg/dL (138–690 nmol/L) for a sample taken at 8 in the morning — and why results are always read against the time of day and the clinical context.
Cortisol is often measured as part of dynamic tests rather than alone. In an ACTH stimulation test, blood is taken before and 1 hour after an injection of cosyntropin; in a dexamethasone suppression test, the sample is taken in the morning after 1 milligram (mg) of dexamethasone the night before. The expected result in these settings can legitimately sit outside the normal range. The test may also be ordered in acute adrenal crisis, sepsis, and low blood pressure.
A cortisol test alone cannot diagnose the cause of an abnormal level — further tests follow. The most common cause of an abnormal result is not a disease at all: taking steroid medicines for a long time, or suddenly stopping them. Stress, pregnancy, exercise, hot and cold temperatures, and medicines such as birth control pills also move the level. In some people high cortisol comes and goes — pseudo-Cushing's syndrome, also called non-neoplastic hypercortisolism — which may be caused by depression, anxiety, alcohol use disorder, poorly controlled diabetes, obesity, and other health problems.
When it is high
Steroid medicinesTaking high doses of certain steroid medicines for a long time — for asthma, rheumatoid arthritis, lupus, and other conditions — is the most common cause of a high result.
Cushing syndromeThe pituitary gland makes too much ACTH because of excess growth or a tumor of the pituitary, driving the adrenal glands to overproduce cortisol.
Ectopic Cushing syndromeA tumor outside the pituitary or adrenal glands — including in the lungs — makes too much ACTH.
Adrenal tumorA tumor of the adrenal gland itself produces too much cortisol.
Stress and acute illnessBoth raise cortisol, as do hot and cold temperatures, exercise, and pregnancy.
When it is low
Addison diseaseThe adrenal glands do not produce enough cortisol; common causes include damage from autoimmune diseases and certain infections, including tuberculosis and HIV.
Secondary adrenal insufficiencyThe pituitary gland does not signal the adrenal gland to produce enough cortisol — from autoimmune diseases, pituitary problems, traumatic brain injury, or surgical removal of the pituitary.
Suppression by glucocorticoid medicinesPills, skin creams, eye drops, inhalers, joint injections, and chemotherapy can suppress normal pituitary or adrenal function — as can suddenly stopping steroid medicines.
What can skew the result
These factors can shift the value without any disease — worth considering before a retest:
Time of day — highest in the early morning, lowest around midnightStress, exercise, hot and cold temperaturesPregnancySteroid medicines (including pills, creams, eye drops, inhalers, joint injections) and suddenly stopping themBirth control pills and certain other medicines
How to prepare
Preparation depends on the type of cortisol test, and the provider's instructions take precedence. Stress and exercise raise cortisol, so rest may be needed before the test; a blood test is usually scheduled for the morning, when the level is at its daily peak.
When a retest makes sense
An abnormal cortisol result is followed by more tests to find the cause — often an ACTH stimulation test or a dexamethasone suppression test, whose expected results deliberately fall outside the normal range. High cortisol that comes and goes (pseudo-Cushing's syndrome) is investigated the same way.
Who usually reviews this result
A result outside the reference range is usually reviewed by: an endocrinologist. Bring your lab report and any previous results to the appointment.
Names used on lab reports
Your report may use any of these names: Blood cortisolPlasma cortisolCortisol serumFree cortisol
Units and conversion
Measured in: mcg/dL
mcg/dL=nmol/L
mcg/dL × 27.59 = nmol/L. Example: 10 mcg/dL = 276 nmol/L. Results are rounded to 2 decimal places.
Several markers on your report?
See how MedProtect explains results in the app: the whole report, a check of the recognized values, and a clear breakdown.
Cortisol follows a daily rhythm — highest in the early morning, lowest around midnight. The reference range is tied to the hour of the draw, so a value that is normal at 8 a.m. can be abnormal at midnight.
What are stimulation and suppression tests?
In an ACTH stimulation test, cortisol is measured before and 1 hour after a cosyntropin injection to check pituitary and adrenal function. In a dexamethasone suppression test, the sample is taken in the morning after 1 milligram (mg) of dexamethasone the night before. Expected results in these tests follow their own rules.
Can stress alone explain a high result?
Yes — stress, acute illness, exercise, extreme temperatures, and pregnancy all raise cortisol. High levels can also come and go (pseudo-Cushing's syndrome) with depression, anxiety, alcohol use disorder, poorly controlled diabetes, or obesity, which is why an abnormal result leads to more tests rather than a diagnosis.
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