Dexamethasone Suppression Test

Overview

The dexamethasone suppression test is a blood test that checks how well your body controls a hormone called cortisol. Cortisol is your body's main stress hormone. It helps you wake up, keeps your blood sugar steady, and helps you cope with illness or stress. Your body normally makes cortisol in a daily rhythm and slows production down when levels are already high. For this test, you take a small measured dose of a man-made steroid tablet (dexamethasone) at a set time, usually late at night. The tablet acts like cortisol and should signal your body to make less of its own. A blood test the next morning shows whether your body 'switched off' as it should. If cortisol stays high, it can be a sign that something is affecting the hormone glands or the signals that control them. The test is one piece of a puzzle. It helps your doctor decide what to check next, but it does not give a diagnosis on its own.

Yes. It is a routine test in hormone (endocrine) clinics and is used whenever doctors need to check whether the body is making too much cortisol. Most people who have the test turn out to have normal results.

Anyone can have the test, at any age. It is most often arranged for adults who have signs of too much cortisol, such as weight gain around the middle, easy bruising, or high blood pressure that is hard to control. It can also be used in children who are gaining weight or growing slowly for no clear reason, and in older adults whose symptoms might at first be blamed on ageing.

Symptoms

Common symptoms

• The test itself has no symptoms. It is arranged because of signs like these.
• Weight gain around the middle of the body, while the arms and legs stay thin.
• A rounder face, sometimes called a 'moon face'.
• Easy bruising and skin that heals slowly.
• Purple or pink stretch marks, often on the tummy, thighs, or breasts.
• Muscle weakness, especially in the thighs and shoulders, making stairs or standing up harder.
• Feeling very tired, or having trouble sleeping.
• High blood pressure or high blood sugar found on a routine check.
• Mood changes, feeling low, or feeling unusually anxious or irritable.
• Periods that become irregular or stop.
• In children: growing more slowly than expected, or putting on weight without a clear reason.

Symptoms in children

• Slower than expected growth, so a child may fall behind on their growth chart.
• Weight gain, especially around the middle and face.
• Feeling very tired or weak during play or sport.
• Changes in mood or behaviour.
• Delayed puberty, or puberty that does not progress as expected.

Symptoms in older adults

• High blood pressure that is hard to control with usual treatment.
• Thin, fragile skin and bruising that appears with very little knocks.
• Muscle weakness that makes getting out of a chair or climbing stairs difficult.
• High blood sugar, or diabetes that suddenly becomes harder to manage.
• Tiredness or low mood that is put down to getting older, when it may be worth checking.
• Bone thinning (osteoporosis) found on a scan.

Causes

Main causes

• The test is done to look for Cushing's syndrome. This is the medical name for having too much cortisol in the body over a long time.
• The most common cause of too much cortisol is taking steroid medicines for another condition, such as asthma, arthritis, or an inflammatory illness. Steroids can be taken as tablets, injections, creams, or inhalers.
• A small non-cancerous growth in the pituitary gland (a pea-sized gland at the base of the brain) can make too much of the hormone that tells the adrenal glands to produce cortisol.
• A growth in one of the adrenal glands (small glands that sit on top of the kidneys) can make extra cortisol.
• Rarely, another part of the body can make the hormone that drives cortisol production.
• Sometimes the test is used to check a lump found on an adrenal gland by chance on a scan, or to look into high blood pressure or bone thinning in a younger person.
• A single abnormal result can also happen for other reasons, including stress, illness, some other medicines, or drinking a lot of alcohol. That is why the test is rarely used alone.

Risk factors

• Taking steroid medicines for more than a few weeks, especially as tablets or injections.
• Having a condition that has needed repeated or high-strength steroid treatment.
• A family history of hormone gland problems or tumours of the pituitary or adrenal glands.
• Having other hormone conditions, such as thyroid problems, that can run alongside these.
• Heavy or long-term alcohol use, which can affect test results.
• Being very unwell or under major stress at the time of testing, which can raise cortisol temporarily.

When to see a doctor

See a doctor urgently if:

• You have several of the signs listed above and they are getting worse quickly.
• You have very high blood pressure with headaches, visual changes, or chest pain. Call your local emergency number for these.
• You take steroid medicines and become very unwell with vomiting, diarrhoea, or severe weakness. Do not stop your steroids suddenly. Get medical help the same day.
• You have a severe reaction to the test tablet.

Book a routine appointment if:

• You have noticed weight gain around the middle, easy bruising, or purple stretch marks over weeks or months.
• You feel persistently tired, weak, or low in mood and cannot explain why.
• Your blood pressure or blood sugar is hard to control.
• Your periods have become irregular or stopped for no clear reason.
• You have been told you may need this test and you want to understand what it involves.
• You are worried about symptoms and would like them checked.

Diagnosis

The dexamethasone suppression test is one part of working out whether your body is making too much cortisol. Your doctor will first ask about your symptoms, your medical history, and any steroid medicines you take, including creams and inhalers. They will examine you and check your blood pressure. The test itself is then arranged, usually at a hospital clinic or a specialist hormone clinic. Sometimes it is done as a short version (an overnight test) and sometimes as a longer version over two days, depending on what your doctor needs to know. The result is always read alongside your symptoms and other tests.

Tests that may be done

• A blood test for cortisol in the early morning, after you have taken the test tablet the night before.
• A blood test for ACTH, the hormone that tells your adrenal glands to make cortisol.
• A late-night saliva sample, to see whether cortisol is falling in the evening as it should.
• A 24-hour urine collection, which measures how much cortisol your body made over a whole day.
• Repeat cortisol tests on more than one day, because a single reading can be misleading.
• Blood tests for blood sugar, salts, and other hormones such as thyroid hormone.
• A scan such as an MRI of the brain or a CT scan of the adrenal glands, if the hormone tests suggest a problem.
• A bone density scan, because long-term high cortisol can thin the bones.

What to expect at your appointment

You will usually be given clear written instructions before the test. You may be asked not to eat for a set number of hours, and you may need to avoid caffeine or alcohol for a day. Tell your doctor and pharmacist about every medicine you take, including ones you buy yourself, because some can affect the result and may need to be paused or timed differently. On the day, you take the tablet at the exact time you are told, then have a blood test the next morning. The blood test feels like a normal blood draw: a tight band, a quick scratch, and a few minutes of pressure afterwards. You may get a small bruise. Some people feel a little flushed or have a mild stomach ache after the tablet. Results usually come back within days to a couple of weeks, and your doctor will explain what they mean and what, if anything, happens next.

Treatment

The dexamethasone suppression test is a test, not a treatment, so there is nothing to 'cure'. What happens next depends entirely on the result. A normal result is good news and usually means no further hormone testing is needed, although your doctor may still look into your symptoms. An abnormal result does not confirm a diagnosis. It usually leads to more tests to find the cause, and treatment is then aimed at that cause.

Self-care at home

• Follow the preparation instructions exactly. The timing of the tablet matters a great deal.
• Write down all your medicines, including creams, inhalers, and anything you buy without a prescription, and show the list to your doctor or pharmacist.
• Avoid alcohol for at least 24 hours before the test unless your clinic tells you otherwise.
• Try to keep your usual sleep and meal routine in the days before testing, since stress and shift work can affect results.
• Don't stop any prescribed medicine on your own. Always check with your doctor or pharmacist first.
• Bring a note of your symptoms and when they started. It helps your doctor interpret the result.
• Drink water normally and eat something after your blood test, especially if you felt faint.
• Ask when and how you will get your results, so you are not left wondering.

Medical treatments

There is no treatment for the test itself. If tests show that your body is making too much cortisol, your specialist team will explain the options. Where a steroid medicine you take for another condition is the cause, the team will usually work with you to lower the dose slowly and safely, or to switch to a different way of taking it. Never change or stop steroids suddenly, because the body needs time to adjust. If a growth on the pituitary or adrenal gland is found, surgery to remove it is often the main option, sometimes followed by radiotherapy. Other medicines can be used in some situations to reduce cortisol production or block its effects, and these are always prescribed and monitored by a specialist. Whatever the cause, the aim is to bring cortisol back to a healthy level and to treat the problems it has caused, such as high blood pressure, high blood sugar, or bone thinning.

When is surgery considered?

Surgery is considered when a scan finds a growth in the pituitary gland or an adrenal gland that is making extra cortisol. An operation to remove the growth can cure the problem in many people. Your specialist team will explain the risks and benefits, what recovery involves, and whether any other treatment is needed afterwards. Not everyone with an abnormal test needs surgery, and many people are treated in other ways.

Living with this condition

Waiting for test results can feel unsettling. Try to keep to your normal routine and remind yourself that one test rarely gives the whole answer. If your results lead to more appointments, keep a simple notebook of your symptoms, your blood pressure or blood sugar readings if you check them, and any questions you want to ask. That makes each appointment easier and helps you feel more in control.

Lifestyle tips

• Keep taking any prescribed medicines exactly as directed unless your doctor tells you otherwise.
• Build gentle activity into your day, such as short walks, to help with mood, sleep, and muscle strength.
• Protect your skin and bones: avoid bumping into things, and ask about vitamin D and calcium if your doctor thinks your bones may be affected.
• Get enough sleep and keep regular hours where you can.
• Limit alcohol, which can affect both cortisol and your test results.
• If you are finding things hard, tell someone. Practical help with shopping, childcare, or work can take real pressure off.

Diet and exercise

There is no special diet that changes cortisol. Eating regular, balanced meals with plenty of vegetables, some protein, and whole grains helps steady your energy and blood sugar. If your blood sugar is high, your doctor may suggest specific changes and may refer you to a dietitian. Gentle, regular movement is helpful. Try walking, swimming, or light strength work with bands or body weight. Build up slowly, because too much too soon can be tiring and can strain weak muscles. A physiotherapist can suggest safe exercises if you feel weak.

Mental health and emotional wellbeing

Hormone changes can affect mood, sleep, and energy, and it is very common to feel worried, low, or irritable while you are being investigated. This is not a sign of weakness, and it is not 'all in your head'. Tell your doctor how you are feeling. Talking therapies, support groups, and practical help can all make a difference. If at any point you feel you cannot keep yourself safe, contact your local emergency number or a crisis support line in your country straight away, and reach out to someone you trust.

Prevention

You cannot prevent the need for a test, but you can make your result more reliable. Follow the preparation instructions closely, be honest about every medicine and supplement you take, and tell your clinic if you have been unwell, had a recent infection, or are under unusual stress. If you take steroid medicines long term, ask your doctor to review your dose regularly. That is the single most useful way to reduce the chance of steroid-related hormone problems.

Screening programmes

The dexamethasone suppression test is not used as a general screening test for healthy people. It is used when there is a reason to check cortisol. If you have a lump on an adrenal gland found by chance, or a family history of hormone gland problems, your doctor may suggest checks. Ask them what is right for you.

Complications

If left untreated

• If the test shows a real problem and it is not followed up, long-term high cortisol can raise the risk of type 2 diabetes and high blood pressure.
• Bones can become thin and break more easily.
• Muscles can become weak, making everyday tasks harder.
• The immune system can be weakened, so infections happen more often or heal slowly.
• Mood can be affected, with low mood, anxiety, or trouble sleeping.
• Periods can stop, and fertility can be affected.
• The test itself has very few risks: a small bruise or sore arm from the blood test, and occasionally a mild upset stomach or flushing after the tablet. A serious allergic reaction is very rare.

Long-term outlook

The outlook is good for most people. Many people who have this test get a normal result and need no further hormone treatment. If a problem is found, it can usually be treated, often very successfully, especially when it is caught early. Treatment may take time and involve a specialist team, but the aim is to bring your hormones back into balance and to help you feel like yourself again. Most people are glad they had the test, because it gives clear answers and a plan.

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