Adrenal . Patient guide
Cortisol
Also known as: Hydrocortisone (synthetic form), Stress hormone (lay term)
What is Cortisol
Cortisol is the main glucocorticoid hormone produced by the adrenal glands. A blood cortisol level measured in the morning is the standard first-line test of how the hypothalamic-pituitary-adrenal axis is functioning.
This biomarker entry is being clinically reviewed by our team. The factual content draws on UK guidance (NICE, NHS, Royal Colleges and the relevant speciality society where cited).
Reference range
Reported in nmol/L. Final reports always carry the issuing laboratory's range, which is what your clinician will interpret against.
| Group | Range | Note |
|---|---|---|
| Morning (8 to 9 AM, serum) | 140 to 700 | nmol/L; assay-dependent (Roche Elecsys Cortisol II is closer to 170 to 540 nmol/L; UK labs vary) |
| Afternoon (4 PM serum) | 83 to 360 | used in dynamic testing only |
| Suggests adrenal insufficiency (AM) | below 140 | requires confirmatory short Synacthen test |
| Persistently above upper reference (AM) | above 700 | a single raised AM cortisol is not diagnostic; if Cushing's syndrome is suspected clinically, an overnight low-dose dexamethasone suppression test, late-night salivary cortisol, or 24-hour urinary free cortisol is the standard next step (NICE CKS Cushing's) |
What it is
Cortisol is released by the outer cortex of the adrenal glands in response to ACTH from the pituitary. It follows a strong daily rhythm: levels peak in the first hour after waking and fall throughout the day to a low point overnight. Cortisol regulates blood glucose, blood pressure, the immune response, and the body's response to physical and psychological stress.
Why a clinician would order it
Cortisol is checked in unexplained fatigue, persistent weight gain or weight loss, low blood pressure with dizziness, salt craving, weakness, central weight gain with thin limbs, easy bruising, or any clinical suspicion of Addison's disease or Cushing's syndrome. It is also frequently requested in the work-up of stubborn hair shedding alongside the broader hormone panel, since prolonged cortisol elevation can disrupt the hair growth cycle.
If your level is outside the range
Symptoms of low Cortisol
- Persistent fatigue, even after sleep
- Light-headedness on standing
- Salt craving
- Unexplained weight loss
- Darkened skin in palmar creases or scars (Addison's)
- Loss of body hair (in women, late sign)
- Low blood pressure
What low can indicate. Primary adrenal insufficiency (Addison's disease), secondary adrenal insufficiency from pituitary disease, or suppression of the HPA axis from long-term oral or topical steroid use. A single low result needs a confirmatory short Synacthen test.
Symptoms of high Cortisol
- Central weight gain with thin arms and legs
- Round, flushed face
- Easy bruising
- Stretch marks (purple striae)
- High blood pressure
- Mood changes, irritability, low mood
- Diffuse hair shedding (telogen effluvium pattern)
- Poor sleep, particularly waking at 3 to 4 AM
What high can indicate. Genuine Cushing's syndrome (uncommon), pseudo-Cushing's from chronic stress, depression, or heavy alcohol use, oestrogen-containing oral contraceptive (raises total cortisol via binding protein), pregnancy, or acute illness on the day of testing.
Testing tips
Cortisol should be drawn in the early morning (typically between 8 and 10 AM, ideally close to 9 AM) after a normal night's sleep, without exercise, smoking, or coffee in the preceding hour. Mention any oral contraceptive (raises measured total cortisol), steroid creams or inhalers, or recent acute illness when discussing your result. A single result is rarely diagnostic on its own; dynamic testing (Synacthen for low, dexamethasone suppression for high) is the next step if needed.
Where you can get this tested
Cortisol is included in the following WMG Health panels. Same-day appointments at our Harley Street clinic, with results clinician-reviewed.
Want a specific combination of markers we do not have a panel for? Build a custom panel and our clinicians will design one for you.
Looking to book a test?
Private adrenal function blood test
Morning cortisol + DHEA-S + testosterone + SHBG, drawn 8 to 9 AM for accurate HPA-axis interpretation. From £180. Adrenal Function Panel £299.
Symptoms often investigated with Cortisol
Cortisol is commonly tested when patients present with the following symptoms. If any of these resonate with you, the linked guides explain what to look for and which test pathway is appropriate.
Sources
UK guidance our clinicians use when interpreting this marker.
This page is general patient information, not personal medical advice. A GMC-registered clinician will review your results and tailor any interpretation to you. See our Editorial Policy for how we write and review content.
Common questions about Cortisol
What is a normal Cortisol range?
Morning (8 to 9 AM, serum): 140 to 700 (nmol/L; assay-dependent (Roche Elecsys Cortisol II is closer to 170 to 540 nmol/L; UK labs vary)). Afternoon (4 PM serum): 83 to 360 (used in dynamic testing only). Suggests adrenal insufficiency (AM): below 140 (requires confirmatory short Synacthen test). Persistently above upper reference (AM): above 700 (a single raised AM cortisol is not diagnostic; if Cushing's syndrome is suspected clinically, an overnight low-dose dexamethasone suppression test, late-night salivary cortisol, or 24-hour urinary free cortisol is the standard next step (NICE CKS Cushing's)). Always interpret your own results against the laboratory range printed on your report, since assay-specific reference ranges vary.
What does a low Cortisol result mean?
Primary adrenal insufficiency (Addison's disease), secondary adrenal insufficiency from pituitary disease, or suppression of the HPA axis from long-term oral or topical steroid use. A single low result needs a confirmatory short Synacthen test.
What does a high Cortisol result mean?
Genuine Cushing's syndrome (uncommon), pseudo-Cushing's from chronic stress, depression, or heavy alcohol use, oestrogen-containing oral contraceptive (raises total cortisol via binding protein), pregnancy, or acute illness on the day of testing.
Do I need to fast or prepare for the Cortisol blood test?
Cortisol should be drawn in the early morning (typically between 8 and 10 AM, ideally close to 9 AM) after a normal night's sleep, without exercise, smoking, or coffee in the preceding hour. Mention any oral contraceptive (raises measured total cortisol), steroid creams or inhalers, or recent acute illness when discussing your result. A single result is rarely diagnostic on its own; dynamic testing (Synacthen for low, dexamethasone suppression for high) is the next step if needed.
Can I order a Cortisol blood test privately in London?
Yes. WMG Health offers Cortisol as part of bespoke panels and several pre-built panels at our 134 Harley Street clinic. Results are clinician-reviewed by a GMC-registered doctor within 4 hours for the most common assays. Bespoke panels from £180; bookings via /contact/ or 020 3239 3378.