Tests for Cushing's syndrome (Investigation of Cushing's syndrome (hypercortisolism))
A step-by-step set of hormone tests used to find out whether your body is making too much of the stress hormone cortisol, and if so, why.
✓ Medically reviewed by a GMC-registered consultant · last reviewed September 2026 · next review September 2027 · how we review
In short
- These tests answer two questions in turn: is cortisol too high, and if so, what is causing it.
- No single test is definitive, so abnormal results are usually repeated or combined before any diagnosis is made.
- Several common things (alcohol, depression, obesity, the pill, pregnancy) can raise cortisol falsely, so careful interpretation matters.
- If steroid medicines are the cause, the answer is often in your medicines list rather than in a scan.
A plain-English summary. The detail — including risks and recovery — is below.
At a glance
A general guide. Your specialist will give you advice for your situation.
Can confirm or rule out genuine cortisol excess rather than relying on symptoms alone
Testing without first reviewing steroid medicines, since exogenous steroids are the most common cause and may make further tests misleading.
Most tests are quick and usually not painful. Blood tests take minutes; saliva and urine collections are done in your own time at home.
A named endocrinologist who explains the whole set of results, not just one number.
Most tests are quick and usually not painful. Blood tests take minutes; saliva and urine collections are done in...
Individual blood, saliva or urine results usually return within days, though your team may wait for several before...
If a test is borderline it is often repeated. Confirming or excluding Cushing's syndrome commonly takes more than...
You move to cause-finding tests (blood ACTH, then scans), which add further appointments before a clear answer.
What does investigating Cushing's syndrome involve?
Cushing's syndrome means your body is exposed to too much cortisol, a hormone that helps you handle stress and control blood sugar, blood pressure and weight. Too much of it over time can cause weight gain around the middle, a rounder face, thin skin that bruises easily, high blood pressure, raised blood sugar and low mood. The most common cause is taking steroid medicines (such as prednisolone) for a long time; less often the body itself overproduces cortisol because of a small growth in the pituitary gland (called Cushing's disease) or in an adrenal gland.
There is no single test that gives the answer. Instead, an endocrinologist works through the question in stages. The first stage simply asks: is cortisol genuinely too high? This usually uses two of these tests: an overnight dexamethasone suppression test, one or two late-night saliva samples, or a 24-hour urine collection. The second stage, only if cortisol is high, works out the cause using blood ACTH levels and scans.
The tests are sensitive but not perfect. Several everyday things can push cortisol up without true Cushing's syndrome, including heavy alcohol use, depression, severe obesity, poorly controlled diabetes, pregnancy and the combined contraceptive pill or oral HRT. This is why one abnormal result is rarely enough on its own and why the process can feel slow.
Types, options & approaches
There may be different ways to do this. The right approach depends on the clinical question and your circumstances.
Options at a glance
These are the main approaches described in this guide. The right option depends on the diagnosis, your goals and what your clinician thinks is safe.
Overnight dexamethasone suppression test
You take a 1 mg dexamethasone tablet at about 11pm and have a blood cortisol test the next morning. Normally the tablet switches cortisol off; in Cushing's syndrome it often...
Late-night salivary cortisol
You spit into a small tube late at night at home, usually on two separate nights. Cortisol should be at its lowest then, so a high level is a useful warning sign.
24-hour urinary free cortisol
You collect all your urine over a full day into a container. It measures the total cortisol your body releases, but it can miss milder cases.
Low-dose dexamethasone suppression test
A longer version using small doses of dexamethasone over two days, sometimes used when the simpler tests are unclear.
Preparing for your test
- Bring an up-to-date list of all your medicines, including steroid tablets, inhalers, creams, joint injections, the contraceptive pill and HRT, as several affect the results.
- Tell your endocrinologist if you might be pregnant, as pregnancy changes cortisol levels and how tests are read.
- Mention heavy alcohol use, shift work, recent severe stress, depression or poor sleep, because these can raise cortisol without true Cushing's.
- Some medicines (for example certain epilepsy drugs, rifampicin, fluoxetine) may need reviewing 4 to 6 weeks beforehand; never stop anything without advice.
- For saliva tests, avoid eating, brushing your teeth, smoking or vaping shortly before the sample, and follow the timing instructions exactly.
- For urine collections, follow the start and stop times carefully and avoid drinking very large amounts of fluid, which can distort the result.
- Ask whether to take dexamethasone at the precise time stated, as timing strongly affects the test.
What happens
Most of these tests are done as an outpatient and many are started at home. For the overnight test you swallow a single tablet at night and attend for a morning blood test. For saliva tests you collect samples yourself at home and return them. For a urine collection you are given a large container and instructions on exactly which day to use.
If the first-stage tests confirm that cortisol is high, you will usually have a blood test for ACTH and may then need a scan of the pituitary gland (an MRI) or the adrenal glands (a CT). A small number of people need a specialist hospital test such as inferior petrosal sinus sampling, which is done by a radiologist to pinpoint where excess ACTH is coming from.
Throughout, your endocrinologist is looking at the pattern across several tests rather than any single number, and will explain what each result does and does not mean.
Is this test right for me?
A good consultation should explore whether it's the right choice for you now — including reasons to wait or consider something else.
May not be suitable if…
- Testing without first reviewing steroid medicines, since exogenous steroids are the most common cause and may make further tests misleading.
- Relying on a single random cortisol blood test, which does not diagnose or exclude Cushing's syndrome.
- Testing during acute severe illness, major stress or untreated depression, when results are hard to interpret.
- Using a 24-hour urine test alone in mild cases, where it often misses the diagnosis.
Delay or rearrange if…
- You are acutely unwell, in hospital or under major physical stress, which raises cortisol.
- You are drinking heavily or have untreated depression, until these are addressed where possible.
- You are on a short course of steroids or recently had a steroid injection.
- You might be pregnant, until your endocrinologist advises how to proceed.
- Key medicines that interfere with the test have not yet been reviewed.
Alternatives to discuss
- No testing if symptoms are clearly explained by steroid medicines, with a medicines review instead.
- Watchful waiting with repeat testing later if early results are borderline.
- Treating contributing factors first (alcohol, depression, blood sugar) and retesting.
- Referral to a different specialty if symptoms point elsewhere.
Before you decide
Use this as a shared-decision checklist. The aim is not just “can this be done?”, but whether it is right for you, now, with the risks and alternatives clearly understood.
What matters most to me?
Think about symptoms, daily life, work, caring responsibilities, sport, fertility, travel, appearance and anxiety — the right choice depends on your priorities, not just the medical facts.
What are all my options?
Ask about waiting, monitoring, medicines, rehabilitation, a smaller or larger procedure, a different test, NHS referral, or a second opinion where that would help.
What would make me pause?
Active infection, pregnancy, unstable medical problems, smoking, medicines that increase bleeding, poor support at home, or feeling pressured are all reasons to slow down and get tailored advice.
What happens if I do nothing today?
For some problems, waiting is safe; for others, delay can make treatment harder. A good consultation should explain the trade-off in plain English.
Benefits
- Can confirm or rule out genuine cortisol excess rather than relying on symptoms alone
- Helps separate true Cushing's syndrome from common look-alike causes
- Identifies whether the cause is steroid medicines, the pituitary gland or an adrenal gland
- Guides the right treatment and avoids unnecessary surgery
- Provides a baseline to monitor against if treatment is started
Risks & complications
- Inconvenience of repeated tests, early starts and home collections
- Bruising or discomfort from blood tests
- Borderline or unclear results that need repeating
- False positives from alcohol, depression, obesity, pregnancy, the pill or HRT
- False negatives that miss mild or cyclical cortisol excess, so testing may be repeated over time
- Anxiety and uncertainty while waiting through several rounds of testing
- Incidental findings on scans (for example a small adrenal lump) that need further checks
- Complications from specialist hospital tests such as petrosal sinus sampling, which your team will explain separately
- A short-lived flushed feeling or, very rarely, an allergic reaction to test medicines used in some protocols
The biggest pitfall is reading a single abnormal result as a diagnosis. Cortisol naturally rises with stress, illness, alcohol, depression and some medicines, and the contraceptive pill or oral HRT can push results up by raising a carrier protein in the blood. Ask your endocrinologist how many tests will be used, what could be causing a false result in your case, and what the plan is if results disagree.
Published figures to discuss
Test accuracy varies and depends heavily on choosing the right test and ruling out look-alike causes. The figures below come from reviews of screening tests and describe how often each test correctly flags true cases (sensitivity) and how often it correctly clears people without the condition (specificity). They are not guarantees for any individual.
| Figure | Reported range | How to interpret it | Source / confidence |
|---|---|---|---|
| Overnight 1mg dexamethasone test — true cases detected | Sensitivity reported above 95%, with specificity around 70-80% | Very good at not missing cases, but a fair number of false positives, so abnormal results are confirmed with another test. | The investigation of Cushing syndrome (review) — PMCpmc.ncbi.nlm.nih.govPublished figure |
| Late-night salivary cortisol — accuracy | Meta-analysis sensitivity around 92% and specificity around 96% | Useful first-line test; usually repeated on two nights and combined with another test. | The investigation of Cushing syndrome (review) — PMCpmc.ncbi.nlm.nih.govPublished figure |
| 24-hour urinary free cortisol — clearing healthy people | Specificity reported around 40-50% in some reviews | Can read high in people without Cushing's (for example with high fluid intake), so it is of limited value in mild cases. | The investigation of Cushing syndrome (review) — PMCpmc.ncbi.nlm.nih.govPublished figure |
These are literature figures, not a personalised prediction. Your own risks and likely benefits depend on your circumstances, your health, and how your care is carried out and followed up.
What happens afterwards
There is no physical recovery from these tests. What matters afterwards is how the results fit together and what the next step is, which often means more than one appointment.
- Feeling that the process is slow and step-by-step rather than giving one quick answer
- Being asked to repeat a test that came back borderline
- Mild bruising at blood-test sites
- Some uncertainty while waiting for the full set of results
Aftercare
- Keep a note of which tests you have done and when, so nothing is repeated unnecessarily.
- Restart any medicines exactly as advised if you were asked to pause them for a test.
- Follow timing instructions precisely for any repeat saliva, urine or tablet tests.
- Ask for your results to be explained in plain terms, including what is still uncertain.
- Tell your team if your symptoms change or worsen while testing continues.
- Make sure you know who to contact about results and the next appointment.
- Full, up-to-date medicines list (including pill, HRT, steroids, inhalers, creams)
- Note of any recent steroid injections into joints or skin
- Record of alcohol intake and sleep/shift pattern to share
- Pregnancy possibility checked and mentioned
- Clear written instructions for each home test
- Contact details for results and queries
⚠ Get urgent help if…
- Severe headache with vision changes, especially if a pituitary problem is suspected
- Very high blood pressure with chest pain, breathlessness or severe headache
- Signs of a serious infection (high fever, feeling very unwell), as high cortisol can mask illness
- Severe muscle weakness, marked swelling, or rapid unexplained weight change
- Low mood with thoughts of harming yourself, which needs urgent help
- If you take steroid medicines, any sudden severe illness, vomiting or collapse, which can signal a steroid emergency
Who to contact: your clinician, clinic or test provider first (keep their number to hand). For urgent advice when you can't reach them, call NHS 111. In an emergency, call 999.
General guidance — it doesn't replace the specific advice your specialist gives you.
Results & realistic expectations
A normal set of results makes Cushing's syndrome unlikely, though if symptoms continue your endocrinologist may repeat testing later, as some cases come and go. Abnormal results that agree across more than one test point towards genuine cortisol excess, and the cause-finding tests then guide treatment.
No single result proves or disproves the condition. The tests describe hormone levels at points in time; they cannot, on their own, tell you the cause or guarantee what will happen next. That is why the pattern across several tests, read alongside your symptoms and medicines, matters more than any one number.
Hormone levels can change over time, so a normal result now does not rule out a problem developing later, and a confirmed diagnosis usually needs ongoing monitoring. If symptoms persist despite normal tests, repeat testing months later is common because mild or cyclical Cushing's can be missed at first.
Related tests, treatments or support
These tests are often done alongside checks for the consequences of high cortisol, such as blood pressure, blood sugar (HbA1c), bone density and salt levels. If a cause is confirmed, scans of the pituitary or adrenal glands and, occasionally, specialist sampling tests are added to complete the picture.
Follow-up & long-term care
You will normally have a follow-up appointment, or several, to review results together. If the diagnosis is confirmed you will be referred for the appropriate treatment (for example pituitary or adrenal surgery, or a review of steroid medicines) and kept under endocrine follow-up.
- If a diagnosis is confirmed, regular review of cortisol and related blood tests
- Monitoring of blood pressure, blood sugar and bone health
- Review of any steroid medicines that may be contributing
- Repeat testing over time if results are borderline or symptoms persist
Repeat, follow-on and what comes next
- Borderline results are common and frequently lead to repeat testing.
- Some people need testing on more than one occasion because cortisol excess can be mild or come and go.
- If cortisol is confirmed high, further cause-finding tests and scans are usually needed before any treatment.
Ask what happens if the result is unclear or needs repeating, and what is included if further tests or follow-up are needed.
What good aftercare looks like
- A named endocrinologist who explains the whole set of results, not just one number.
- A clear written plan for any repeat tests, with exact timing instructions.
- Prompt onward referral and monitoring if a cause is confirmed.
- Honest acknowledgement of uncertainty when results are borderline, with a safety net for review.
What affects the cost
Costs vary a great deal between people and providers, and we don't publish prices. What matters is understanding what drives the cost and making sure your quote is complete. The main things that affect it:
- Number and type of tests needed (saliva, urine, blood, dexamethasone protocols)
- Endocrinology consultation time and follow-up appointments
- Laboratory and reporting fees, including repeat tests for borderline results
- Any scans required (MRI pituitary or CT adrenal) if cortisol is confirmed high
- Specialist hospital tests such as petrosal sinus sampling in selected cases
- Whether more than one round of testing is needed over time
- The endocrinology consultation fee and likely number of follow-ups
- Which tests are included and the cost of each laboratory test
- Whether repeat testing for borderline results is included
- The cost of any scans if cortisol is confirmed high
- What happens, and what it costs, if results are inconclusive
- Who reports the results and how they are explained to you
On the NHS? Investigation of suspected Cushing's syndrome is normally done on the NHS by an endocrinologist; private testing may be used for speed or a second opinion but should follow the same stepwise approach.
You're entitled to your total cost in writing — including reports, follow-up and what happens if the result is inconclusive — before you decide.
Consent traps and marketing red flags
These are not small details. They are often where patients lose choice, time to reflect, or realistic expectations.
Consent traps
- Being given a diagnosis on the strength of one abnormal test.
- No discussion of how the pill, HRT, alcohol, depression or pregnancy could affect results.
- No clear plan for what happens if results disagree or are borderline.
- Pressure to proceed to scans or surgery before cortisol excess is properly confirmed.
Marketing red flags
- Private clinics offering a single 'cortisol test' as a definitive check for Cushing's.
- Promising a quick yes/no answer when the proper process is stepwise.
- Bundling unnecessary scans before cortisol excess is confirmed.
- Downplaying the common false-positive causes.
Choosing a specialist safely
- Check the specialist is on the GMC Specialist Register for this area.
- Make sure they work at a CQC-registered service, and look for membership of the relevant Royal College or professional body.
- You're entitled to time to consider and to have your questions answered before you agree — the specialist who looks after you should explain it, not a salesperson.
- Be wary of pressure: time-limited offers or deposits taken before you've had time to think are red flags, not bargains.
- You're entitled to your total cost in writing — including any follow-up — before you decide.
Questions to ask your medical professional
Take this to your consultation. A good specialist will welcome every one of these.
- Which tests are you using to confirm whether my cortisol is high, and why those?
- Could any of my medicines, alcohol intake, mood or pregnancy be affecting the results?
- What will you do if my results disagree with each other or come back borderline?
- If cortisol is confirmed high, what are the next steps to find the cause?
- What happens if all the tests are normal but my symptoms continue?
- Who do I contact about my results and the next appointment?
- Are you on the GMC Specialist Register for this area, and which Royal College or professional body are you a member of?
- Will you be the specialist who carries out my test, and who looks after me afterwards?
- What are the risks for someone like me, and how often do your own patients have a problem or need it repeated or redone?
- What does a realistic result look like — and what can this test not achieve?
- What are my options, including waiting, doing nothing for now, or choosing a different approach?
- Can I have written information, results and aftercare instructions in a format I can use, including any accessibility or communication support I need?
- What is the total cost in writing, including any follow-ups, and how much time do I have to decide?
Frequently asked questions
Why do I need so many different tests?
Can the contraceptive pill or HRT affect my results?
Is high cortisol on one test the same as having Cushing's syndrome?
Do the tests hurt?
Will I need a scan?
Can I have this investigated privately?
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How we made this page
Medically reviewed by a GMC-registered consultant. Written in plain English, checked against NHS, NICE, GMC and relevant Royal College / specialist-society guidance, and kept under review. No clinic paid to appear on this page, and we publish no pricing. This is general information to help you prepare — it is not a substitute for advice from your own clinician. How we review our guides →
Source hierarchy: UK regulator and NHS/NICE guidance first, then relevant Royal College or specialist-society guidance, then peer-reviewed evidence for procedure-specific figures where available.
Sources & standards: NHS — Cushing's syndrome Society for Endocrinology — What is endocrinology? The investigation of Cushing syndrome (review) — PMC Cushing's syndrome: stepwise approach to diagnosis — PMC Late-night salivary cortisol as a screening test — PMC
Reviews reflect patients' experience of care, not clinical outcomes. For procedure volumes and outcome data see PHIN.
Last medically reviewed 2026-09-21. Spotted something wrong or out of date? Report an error in this guide.
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