At a Glance
Cortisol has two normal ranges, not one. It peaks in the early morning and is much lower by the afternoon, so laboratories publish separate morning and afternoon adult intervals rather than a single band.
The range shown on this page is 2.3 - 19.4 µg/dL, and it is those two intervals flattened into one. Labcorp publishes 6.2 - 19.4 µg/dL for a morning sample and 2.3 - 11.9 for an afternoon one. Take the lower floor and the higher ceiling and you get the single band stored here — which means it is wide enough to contain both, and therefore too wide to be right for either.
That is worth knowing before you read your number. Two ordinary results sit inside the band and outside the interval that actually applies:
- A morning cortisol of 5 µg/dL shows in range here, and is below Labcorp's morning floor of 6.2.
- An afternoon cortisol of 15 µg/dL shows in range here, and is above Labcorp's afternoon ceiling of 11.9.
Laboratories also differ, so if your sample was run elsewhere the boundaries move again:
| Laboratory | Morning | Afternoon |
|---|---|---|
| Labcorp | 6.2 - 19.4 µg/dL (8 a.m.) | 2.3 - 11.9 µg/dL (4 p.m.) |
| Mayo Clinic Laboratories | 7 - 25 µg/dL | 2 - 14 µg/dL |
| ARUP Laboratories | 6.0 - 18.4 µg/dL (6-10 a.m.) | 2.7 - 10.5 µg/dL (4-8 p.m.) |
A morning result of 20 µg/dL shows what that spread means: above Labcorp's ceiling and ARUP's, comfortably inside Mayo's. Read your number against the interval on your own report, and use the collection time to know which of that laboratory's two applies.
The timing matters physiologically, not procedurally. Mayo: "CRH is released in a cyclic fashion by the hypothalamus, resulting in diurnal peaks (6 a.m.-8 a.m.) and troughs (11 p.m.) in plasma ACTH and cortisol levels" — hence "morning (8 a.m.) and afternoon (4 p.m.) specimens are preferred".
A raised total is sometimes not about the adrenal gland at all. A serum cortisol measures total cortisol — the fraction bound to a carrier protein plus the small active free fraction. Mayo names the commonest cause of a raised total in women: "the most common cause of increased plasma cortisol levels in women is a high circulating concentration of estrogen (eg, estrogen therapy, pregnancy) resulting in increased concentration of cortisol-binding globulin."
For estrogen taken by mouth the effect is large: the Endocrine Society reports "false-positive rates for the overnight DST are seen in 50% of women taking the oral contraceptive pill". The route matters — Endotext says systemic estrogens should be stopped before testing, but that "estrogen patches will not affect CBG". How any of this affects follow-up testing is for the ordering clinician to weigh; nothing here is a reason to change a prescribed medication.
Pregnancy is a different case. Cortisol genuinely rises in normal pregnancy and the binding protein is only part of the reason: Endotext describes "a rise in cortisol… partly due to estrogen-stimulated elevation corticosteroid-binding globulin", while "the diurnal secretion is maintained during pregnancy despite these changes." The free fraction rises too — urinary free cortisol "can only be relied upon to distinguish between CS and normal pregnancy if it is more than three times the upper range of normal". So a raised cortisol in pregnancy is not simply a binding-protein artifact, and the Endocrine Society recommends "the use of UFC and against the use of dexamethasone testing in the initial evaluation of pregnant women."
This test does not screen for Cushing's syndrome, and is not meant to. The Endocrine Society is explicit: "we recommend against the use of the following to test for Cushing's syndrome… random serum cortisol or plasma ACTH levels", naming four initial tests instead (in the FAQs). That is about Cushing's specifically — a morning cortisol has a role elsewhere, and Mayo describes a low 8 a.m. value with compatible symptoms as the trigger for further investigation of glucocorticoid deficiency.
Other ordinary things move the number. MedlinePlus lists stress, pregnancy, exercise, temperature extremes and birth control pills — and states the conclusion plainly: "a cortisol test alone can't diagnose the cause of abnormal cortisol levels."
How to read your result
These rows use Labcorp's intervals, because the range stored on this page is built from them. If your sample was run elsewhere, read against the interval on your own report.
| Against Labcorp's intervals — 6.2-19.4 a.m., 2.3-11.9 p.m. | What it means | What happens next |
|---|---|---|
| 6.2 to 11.9 µg/dL, morning or afternoon | Inside both intervals, so neither the draw time nor the laboratory changes this one. But being in range does not cancel the morning rule: Mayo notes that with symptoms of glucocorticoid deficiency, an 8 a.m. value under 10 µg/dL calls for further studies. | Afternoon, or no symptoms: nothing on this result alone. Morning under 10 with symptoms: read the low-cortisol section. |
| 2.3 up to 6.2 µg/dL | Afternoon: inside Labcorp's 2.3-11.9 — the daily trough. Morning: below Labcorp's floor of 6.2, and still shown in range here, because the stored band reaches down to the afternoon floor. | Morning, with symptoms of glucocorticoid deficiency: worth raising even though nothing is flagged. |
| Above 11.9 up to 19.4 µg/dL | Morning: inside Labcorp's 6.2-19.4. Afternoon: above Labcorp's ceiling of 11.9, and still shown in range here — the same flattening, at the other end. | On an afternoon specimen, worth raising with the draw time attached. |
| 19.4 to 25 µg/dL | Above Labcorp's morning ceiling whatever the draw time, and well above its afternoon one. Amber here rather than red because some laboratories run higher — Mayo's morning interval reaches 25. | Check the draw time, the laboratory, and any estrogen-containing medication. |
| Above 25 µg/dL | Above the morning interval at every laboratory in the table. | Take to the clinician who ordered it. Not a diagnosis — a random serum cortisol is not a Cushing's test. |
| Below 2.3 µg/dL | Below both of Labcorp's intervals, and below Mayo's and ARUP's. | Raise it, with any symptoms and any steroid treatment. |
| Any value, on the pill or oral estrogen | The total is raised by the carrier protein — though not by an estrogen patch, which Endotext says does not affect CBG. | Discuss whether a measure unaffected by binding protein is appropriate. |
| Any value, in pregnancy | Cortisol rises in normal pregnancy, and not only through the carrier protein — the free fraction rises too. | The Endocrine Society recommends urine free cortisol, not dexamethasone testing. |
Between 6.2 and 11.9 µg/dL the draw time makes little difference. Outside that span it decides a great deal — and the tracker knows neither your draw time nor your laboratory, while your report carries both.
If you remember only one thing
The band on this page is Labcorp's morning and afternoon intervals flattened into one, so it is too wide for either. A morning 5 µg/dL and an afternoon 15 both show in range here and both sit outside the interval that applies. Read your number against the interval on your own report, and use the collection time to know which of that laboratory's two applies.
Two people, same result
Two people both have a serum cortisol of 21 µg/dL.
The first was drawn at 7:30 a.m. and run by Labcorp, whose morning interval is 6.2 to 19.4 µg/dL. At 21 that is above the ceiling, though only just.
The second was drawn at 4 p.m. Labcorp's afternoon interval is 2.3 to 11.9, so the same number is far above where it should be by then.
A third, drawn at 7:30 a.m. but run by Mayo, is told it is normal — Mayo's morning interval reaches 25. Same figure, three readings, separated by a line on the requisition and a laboratory's name. At 10 µg/dL all three would agree.
What this result cannot tell you
Whether you have Cushing's syndrome. A random serum cortisol is not a test for it.
Whether you have adrenal insufficiency. Mayo describes a low 8 a.m. value alongside symptoms as the trigger for further studies, not the answer.
Whether a high total means high active hormone — if you take estrogen by mouth. The pill and oral estrogen raise the binding protein and with it the total; a patch does not. In pregnancy the free fraction rises as well.
How stressed you are. A single measurement is not a stress score.
Where a result outside 6.2 to 11.9 µg/dL sits — without the collection time. That is where Labcorp's two intervals disagree, and where the single stored band stops being informative.
Common interpretation mistakes
Reading a number above 11.9 without the draw time. Above Labcorp's afternoon ceiling but inside its morning interval, a result shows in range here and may not be.
Comparing a morning result to the band on this page. That band is two intervals flattened into one, so it is wider than the one that applies to you.
Reading a high total on the pill as an adrenal problem. Oral estrogen raises the carrier protein — 50% false positives on the overnight DST, per the Endocrine Society — but that reasoning carries neither into pregnancy, where the free fraction rises too, nor to a patch, which Endotext says does not affect CBG.
Treating a single raised result as a diagnosis. It is not a Cushing's test.
Assuming a low afternoon value is a low result. Mayo's afternoon interval starts at 2 µg/dL.
Questions your doctor may ask
- What time was the blood taken?
- Are you taking the combined pill or estrogen by mouth, are you using a patch, or are you pregnant?
- Are you taking any steroid — inhaled, topical or injected included?
- Have you been acutely unwell or under unusual stress around the test?
- Any weight change, skin changes, bruising, or muscle weakness?
- Any dizziness on standing, unusual fatigue, or salt craving?
Read together with
- ACTH — separates ACTH-driven cortisol excess from an adrenal source producing it independently; pituitary versus ectopic needs further testing again
- Cortisol-Binding Globulin (CBG) — the carrier protein estrogen raises
- Cortisol (7AM-9AM), saliva — measures the unbound fraction
- DHEA-S — the other adrenal steroid, read alongside cortisol
- Glucose — cortisol raises it, and the pair is read together
Clinical pearls
The diurnal rhythm is the interpretive frame outside the overlap. Peaks at 6-8 a.m., troughs around 11 p.m.; Mayo therefore prefers 8 a.m. and 4 p.m. specimens.
Salivary cortisol sidesteps the binding-protein problem. The Endocrine Society notes that "biologically active free cortisol in the blood is in equilibrium with cortisol in the saliva" — which is why late-night salivary cortisol is a recommended initial test.
An adult interval is not one band across a lifetime. Mayo publishes five pediatric intervals from birth to 18, listed in the FAQs.
In pregnancy the recommended test changes — urine free cortisol, not dexamethasone.
Clinical Takeaway
Serum cortisol is a total measurement — bound plus free — with a pronounced diurnal rhythm and two adult reference intervals rather than one, against peaks at 6-8 a.m. and troughs around 11 p.m. The band stored on this page, 2.3-19.4 µg/dL, is Labcorp's two intervals flattened into one (6.2-19.4 a.m., 2.3-11.9 p.m.), so it is wider than whichever applies and under-flags at both ends: a morning 5 and an afternoon 15 both render in range. Boundaries also differ by laboratory (Mayo 7-25 / 2-14; ARUP 6.0-18.4 / 2.7-10.5), so the interval on the patient's own report governs. Oral estrogen raises cortisol-binding globulin and with it the total; in pregnancy cortisol also rises, but not only through the carrier protein, and the recommended initial test changes to urine free cortisol. A random serum cortisol is not recommended as a test for Cushing's syndrome, and a low 8 a.m. value with compatible symptoms indicates further studies rather than a diagnosis.
In one sentence
A serum cortisol is read against the interval printed on your own report, and the collection time tells you which of that laboratory's two adult intervals — morning or afternoon — applies to your number.
Bottom line
Use the interval printed on your own report, and find the collection time to know which half of the day it applies to. The band shown here is Labcorp's two intervals flattened into one, so it is wider than the one that applies to you — a morning 5 and an afternoon 15 both show in range and both sit outside it.
If you take the combined pill or estrogen by mouth, the carrier protein is the first explanation Mayo gives for a raised cortisol in women, ahead of the gland; a patch does not have that effect. In pregnancy cortisol rises too, but for more than that one reason, which is why the guideline recommends a different test.
And whatever the number, a random serum cortisol is not recommended as a test for Cushing's syndrome, and a single low value does not establish adrenal insufficiency. As MedlinePlus puts it, "a cortisol test alone can't diagnose the cause of abnormal cortisol levels."
Cortisol, Serum
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Frequently Asked Questions
What is a normal cortisol level?
What is a normal cortisol level for a woman?
What is the normal cortisol range in µg/dL?
Why does the time of the blood test matter for cortisol?
Can birth control pills raise cortisol?
Does a high cortisol mean Cushing's syndrome?
What does a low cortisol level mean?
My cortisol is 21 µg/dL. Is that high?
Is a high cortisol in pregnancy a problem?
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Why does this page show one range when there are two?
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