Cortisol Blood Test

• Cortisol (measured): total cortisol in a serum sample, including the protein-bound and free fractions.

This test does not include ACTH, a Synacthen stimulation test, a dexamethasone suppression test, salivary cortisol or 24-hour urine cortisol. These are arranged by a GP or endocrinologist when they are needed.

Cortisol production is controlled by the hypothalamic-pituitary-adrenal axis. The hypothalamus signals the pituitary gland to release adrenocorticotropic hormone (ACTH), and ACTH stimulates the outer layer of the adrenal glands to make cortisol. Cortisol then feeds back to reduce ACTH, keeping output in balance.

Cortisol is essential for life. It stimulates glucose production in the liver, helps break down fat and protein, supports blood pressure and heart function, and restrains inflammation and immune activity. Output increases during illness, injury and other physical or emotional stress.

Levels rise in the early hours, peak around 8am and fall through the day to their lowest around midnight. Long-term night-shift work can shift this pattern, and in Cushing's syndrome the night-time fall is often lost. Most cortisol in the blood is carried by binding proteins, and a standard blood test measures this total amount.

Clinicians measure cortisol to look for too little (adrenal insufficiency) or too much (Cushing's syndrome). Each is confirmed with structured tests. The Endocrine Society recommends a corticotropin (Synacthen) stimulation test to confirm primary adrenal insufficiency. For suspected Cushing's syndrome, its guideline recommends urine free cortisol, late-night salivary cortisol or a dexamethasone suppression test, and advises against using a random serum cortisol.

Because cortisol changes so much through the day, reference ranges are tied to the time of sampling, and a result taken outside the 8am to 9am window is hard to interpret. Ranges also depend on the laboratory's method, so use the figures on your report.

In the Endocrine Society guideline on primary adrenal insufficiency, a morning cortisol below 140 nmol/L combined with a raised ACTH is treated as a preliminary indication until a stimulation test can be done. That threshold is assay-dependent, is used by specialists alongside other tests and is not a cut-off for self-diagnosis.

Things that can raise cortisol

• Illness, infection, injury, pain, and physical or emotional stress, including anxiety about the blood test itself
• Strenuous exercise, heat or cold
• Pregnancy and oestrogen-containing medicines such as the combined pill, which raise the binding protein that carries cortisol
• Obesity, an overactive thyroid and some medicines, including spironolactone

Things that can lower or distort cortisol

• Steroid medicines (tablets, inhalers, creams, joint or other injections), which suppress the body's own production and some of which cross-react with the test
• An underactive thyroid
• Night-shift work, which changes the timing of the daily peak

Lab Tests Online UK notes that a single measurement is usually not enough and that repeat testing is common. A low result is less useful on its own for diagnosing Addison's disease, and a high result taken during stress should be repeated when you are well. Where a result may need medical attention, we advise you to see your GP and, with your consent, we can write to your GP.

Symptoms of adrenal insufficiency, such as persistent tiredness, weight loss, low appetite, dizziness on standing, salt craving and darkening of the skin, overlap with many common conditions. Symptoms of Cushing's syndrome include weight gain around the trunk, a rounded face, easy bruising and purple stretch marks. In both cases the NHS route is a GP assessment, with referral to an endocrinologist for confirmatory tests.

The NHS notes that the most common cause of Cushing's syndrome is long-term use of high-dose steroid medicines. If you take steroids and are worried about their effect on your adrenal glands, please speak to your prescriber. Never stop steroid medicine suddenly.

May be useful if you

• have symptoms you are discussing with your GP and want a correctly timed 9am cortisol to bring to that appointment
• have been asked by your own clinician to arrange a morning cortisol

May not be the right choice if you

• feel acutely unwell, are vomiting or have collapsed: call 999 or go to A&E
• want to check for Cushing's syndrome: guidelines advise against a random or single serum cortisol, and your GP can arrange the recommended tests
• take steroid tablets, inhalers, creams or injections: results are often hard to interpret, so discuss with your prescriber first
• are pregnant or using oestrogen-containing medicines, which raise total cortisol
• want a measure of day-to-day stress

• Established use: cortisol testing within structured stimulation and suppression tests to diagnose adrenal insufficiency and Cushing's syndrome.
• Physiology: cortisol follows a daily rhythm that can be disrupted by night-shift work and illness.
• Research use: studies of cortisol patterns usually rely on repeated saliva or urine samples across the day, which a single blood test cannot reproduce.
• Unproven: a single morning blood cortisol cannot measure chronic stress, resilience, burnout or biological ageing, and this test is not designed to assess so-called "adrenal fatigue".

• Timing: book an appointment between 8am and 9am. Please tell us if you cannot attend in this window.
• On the day: avoid strenuous exercise beforehand, and arrive a few minutes early so you can sit quietly before the sample.
• Shift work: tell us if you work nights or have recently changed shifts, as your daily rhythm may be shifted.
• Illness: postpone if you are unwell, unless a clinician has asked for the test during illness.
• Medicines: list every steroid you use, including inhalers, nasal sprays, creams and joint injections in the last few months, plus any contraceptive pill or HRT. Do not stop or change prescribed medicine for this test.
• Biotin: mention any biotin or hair, skin and nail supplement when booking, as high doses can affect some hormone tests.

Choose how your sample is taken when you book. We confirm the collection option, any collection fee and the expected turnaround time before you book.

• Juvenology Clinic, Maidstone (82 King Street, Maidstone ME14 1BH): Available.
• Partner clinic near you, anywhere in the UK: Available on request. We confirm availability for your postcode before you book.
• Postal home finger-prick kit: Ask before ordering. We offer a home kit only where the laboratory confirms this test is suitable for a finger-prick sample.

Sample: Venous blood sample (serum)

Collection notes: Sample must be taken between 8am and 9am. If a home finger-prick kit is offered, it must be collected in this window and the collection time recorded; postal delays and the stress of self-collection can affect interpretation. List all steroid medicines, including inhalers, creams and injections.

The price of this test covers laboratory analysis and the laboratory's results report. The report lists each result beside the laboratory's reference range.

Beyond the blood test: optional support, priced separately

• Personalised written interpretation report: £50
• General consultation: £50
• Results consultation (results discussion and follow-up advice): £100
• Personalised programme: from £150, after we assess whether a programme suits you

Consultations are with Marina, an NMC-registered nurse. She explains what your results show and how they relate to lifestyle. No prescription service is offered with these tests.

If a result suggests you need medical follow-up, we will recommend that you see your GP and, with your consent, can provide a letter to take with you. A blood test cannot rule out every condition. If you have symptoms, speak to your GP or NHS 111, and call 999 in an emergency.

Why does the sample have to be taken between 8am and 9am?

Cortisol peaks in the early morning and falls through the day. Morning reference ranges and clinical thresholds are based on samples taken at this time, so a later sample can look misleadingly low.

Can this test tell me how stressed I am?

No. Cortisol rises briefly with many short-term stresses, including the blood test itself, and one result cannot measure long-term stress or wellbeing.

Can a cortisol blood test diagnose Cushing's syndrome?

No. Guidelines advise against a single serum cortisol for this. Your GP can arrange urine, late-night saliva or dexamethasone suppression testing if Cushing's syndrome is suspected.

I use a steroid inhaler or cream. Will it affect the result?

It can. Steroid medicines may suppress your own cortisol or cross-react with the test. Tell us what you use and do not stop it.

My result was low. What should I do?

Share it with your GP, who may repeat it or arrange a Synacthen stimulation test. If you feel very unwell, are vomiting or faint, seek urgent care straight away.

Is interpretation of my result included?

The price covers laboratory analysis and the laboratory's report with reference ranges. You can add a personalised written interpretation report (£50) or a results consultation (£100).

1. Nieman LK, et al. The Diagnosis of Cushing's Syndrome: An Endocrine Society Clinical Practice Guideline. Journal of Clinical Endocrinology & Metabolism, 2008;93(5). https://www.endocrine.org/clinical-practice-guidelines/diagnosis-of-cushing-syndrome
2. Bornstein SR, et al. Diagnosis and Treatment of Primary Adrenal Insufficiency: An Endocrine Society Clinical Practice Guideline. Journal of Clinical Endocrinology & Metabolism, 2016. https://www.endocrine.org/clinical-practice-guidelines/primary-adrenal-insufficiency
3. Cortisol test. Lab Tests Online UK. https://labtestsonline.org.uk/tests/cortisol-test
4. Cortisol: test information. University Hospitals of North Midlands NHS Trust Pathology. https://www.uhnm.nhs.uk/hospitals-and-services/pathology/tests/cortisol/
5. Addison's disease. NHS. https://www.nhs.uk/conditions/addisons-disease/
6. Cushing's syndrome. NHS. https://www.nhs.uk/conditions/cushings-syndrome/