Cortisol is a steroid hormone made by the adrenal glands and released in a daily rhythm that usually peaks in the early morning. A blood test measures total cortisol in serum, and it is ordered when adrenal or pituitary function is being assessed. The time of the sample matters, and your report's printed range decides how the value is read.
A cortisol result is never just a number. The hour it was collected, the person's sleep pattern, and whether they were unwell at the time all shape what the laboratory sees.
What the test measures
Cortisol is the main glucocorticoid made by the outer layer of the adrenal glands, which sit above the kidneys. Its release is controlled by the pituitary gland, which sends adrenocorticotropic hormone, or ACTH, in response to signals from the hypothalamus. Together these form the hypothalamic-pituitary-adrenal axis, and that axis sets the daily pattern of cortisol.
In a person who sleeps at night and is awake in the day, cortisol is usually highest in the early morning and lowest in the late evening, though the timing shifts with sleep and shift work. Most of the cortisol in blood is bound to a carrier protein called cortisol binding globulin, with some bound to albumin. A blood test measures total cortisol, bound and free together. Saliva and urine tests measure the free fraction, and they answer a different question.
Why it may be ordered
- As part of a hormone panel, with testosterone and prolactin, or with ACTH.
- When a clinician is assessing adrenal or pituitary function, alongside the symptoms and the rest of the assessment.
- When fatigue, weight change, low blood pressure, or unusual skin pigmentation is being investigated.
- When a person takes a glucocorticoid medicine and adrenal suppression is a question, which a clinician may test.
- Alongside a dynamic test, such as an ACTH stimulation test or a suppression test, which are separate procedures.
- When a known adrenal or pituitary condition is being followed over time.
The unit on your report
| What you may see | Unit | What it reflects |
|---|---|---|
| Cortisol, serum cortisol, total cortisol | ug/dL | The total cortisol concentration in serum, bound and free, in micrograms per decilitre. Some reports print the unit with the Greek mu instead of u. |
| Cortisol, serum cortisol | nmol/L | The same measurement in nanomoles per litre. The two scales are not the same number. |
| Cortisol (AM), cortisol (PM) | ug/dL or nmol/L | A line that names the collection time. It is read against a range for that time, not a single range for the day. |
| Free cortisol, salivary cortisol, urine free cortisol | as the laboratory reports | The unbound fraction in a different sample. It is not interchangeable with a serum total cortisol. |
When a report names a collection time, that label is part of the result. A morning value and an evening value from the same person are not two readings of the same thing.
Why this page does not print a range
A cortisol range is built for a laboratory, a method, and a time of collection. Two laboratories can print different ranges for a morning sample, and many reports print separate ranges for morning and afternoon samples. Age, sex, pregnancy, oestrogen-containing medicines, acute illness, and the assay all shift the expected interval, and pregnancy raises the binding protein, which raises total cortisol.
The range printed on the report that produced your value is the one that applies, and the time it was collected is part of that. Doctano keeps the printed range with the result and does not replace it with a general range. When a report prints a time-specific range, read the value against the one that matches the collection time.
What a high value can mean
A result above the report's range means the cortisol concentration is higher than the laboratory's interval for that sample. Possible contributors include overproduction of cortisol by the adrenal glands or excess ACTH from the pituitary, acute illness, pain, surgery, severe stress, pregnancy, oestrogen-containing medicines, and glucocorticoid medicines that affect the measurement or the axis.
A high total cortisol can reflect a high binding protein rather than more free hormone, which is why the collection context and the other hormone results matter. The result does not confirm or rule out any of these, and a clinician reads it with the clinical picture and often with a dynamic test.
What a low value can mean
A result below the report's range means the cortisol concentration is lower than the laboratory's interval. Possible contributors include reduced adrenal output, pituitary or hypothalamic conditions that reduce ACTH, and adrenal suppression after a period of glucocorticoid medicines. A low binding protein, as in liver disease or a protein-losing kidney condition, can also lower total cortisol without changing the free fraction.
Timing can explain a low value too. A late-evening sample is usually much lower than a morning sample, and a range written for the morning does not apply to it. A single low result does not establish adrenal insufficiency, and a clinician reads it with the collection time, sodium and potassium, glucose, and the rest of the picture.
What can move the value
- Time of day. The daily rhythm is the largest single influence on a cortisol result.
- Sleep and shift work. A sleep pattern that differs from the usual night-day cycle shifts the rhythm.
- Acute illness, pain, and stress. Cortisol rises with physical stress, including surgery and infection.
- Pregnancy and oestrogen. Both raise the binding protein, which raises total cortisol.
- Medicines. Glucocorticoid medicines can suppress the axis or interfere with some assays, and a clinician can say whether a medicine is relevant.
- Assay and calibration. Different methods can produce different results, especially at the low end of the scale.
What to compare it with
Read cortisol with ACTH, which shows what the pituitary is signalling; with sodium, potassium, and glucose, which can change when adrenal function changes; and with the other hormones on the panel. Where a clinician is assessing the adrenal axis, a morning and an evening sample, or a dynamic test, often add more than a single value. The collection time is part of every comparison.
How to see the trend
Doctano reads the cortisol value, its unit, and the reference range printed on the report. It keeps the range with the result, normalizes the marker name across laboratories, and places the value on the profile's timeline. Where the report prints a collection time, that stays with the value, so two results from different hours are not quietly treated as the same measurement.
Verify the value and the unit against the original report before treating a change as real, especially when the two samples were collected at different times or in different laboratories.
What this page is not
This page explains the test in general. It does not interpret your result, diagnose a condition, or recommend treatment. It is not medical advice. Verify the value and the unit against the original report, and discuss the result with a qualified professional.