DEXA (dual energy X-ray absorptiometry) scan

Your health expert: Dr Rizwan Rajak , Consultant Rheumatologist
Content editor review by Rachael Mayfield-Blake, November 2023
Next review due November 2026

A DEXA (dual energy X-ray absorptiometry) scan measures the density of your bones, which helps to show how strong they are. It’s used to diagnose osteoporosis (fragile bones) or assess your risk of developing fractures as a result of osteoporosis. A DEXA scan gives your doctor information about how to reduce your risk of breaking a bone.

About DEXA scan

A DEXA scan, also known as a DXA or bone density scan, uses very low levels of X-ray radiation to produce images of your bones. It detects how much radiation is absorbed by your bones, which shows how dense they are. This, plus a fracture risk assessment, is used to predict how likely you are to have a broken bone (fracture) from osteoporosis.

A DEXA scan of your hip and spine is the ‘gold standard’ to diagnose osteoporosis and to predict your risk of breaking a bone. This is because your spine and hip are two of the most common places to break bones if you have osteoporosis.

Another type of DEXA scan is a peripheral DEXA scan. This uses a smaller, portable machine that can measure bone density in your wrist, heel or ankle. It can help to predict your risk of having another fracture although it’s not as good as a standard DEXA scan. But it may give your doctor an idea of whether or not you need to have a full DEXA scan or other tests.

You’ll normally have a DEXA scan at your local hospital. The bone density scan is safe, quick and painless.

Assessment for a DEXA scan

Your doctor or other health professional will refer you for a DEXA scan on the NHS. You may be able to get a DEXA scan at a private hospital or clinic without a referral. But a qualified health professional will need to authorise it. Arrangements vary at different hospitals, so check what your hospital or clinic’s procedures are.

You’ll usually only be invited to have a DEXA scan if your doctor has assessed you as being at risk of osteoporotic fragility fractures. A fragility fracture is when your bones become weakened due to osteoporosis, so that even a minor bump or fall can cause them to break.

Your doctor may ask you to have a fracture risk assessment:

when you reach a certain age – usually 65 and over for women and 75 and over for men
because you’ve previously had a fragility fracture

You may need a DEXA scan at an earlier age if you have certain risk factors. For example, if you:

had an early menopause (before 40)
have a family history of osteoporosis
have a low body mass index (BMI)
are taking steroid tablets

Your doctor will use online tools to calculate your fracture risk. These take into account things that might increase your risk, including your medical history, age, sex, height, weight, and any medicines you take. The calculation also includes lifestyle factors, such as whether or not you smoke, and how much alcohol you drink. This is because these factors also affect your bone density. The tools predict how likely it is that you’ll have a fracture due to osteoporosis in the next 10 years. If your risk is within a certain level, your doctor will advise you to have a DEXA scan.

Preparation for a DEXA scan

You’ll usually have a DEXA scan at an outpatient clinic in your local hospital so you can have the scan and go home the same day. You don’t usually need to do anything before a DEXA scan.

Your hospital will tell you what to wear for a DEXA scan. You may be able to stay in your clothes during the scan if you’re not wearing anything metal. You’ll need to take any keys and wallets out of your pockets and remove any other metal objects, such as glasses, piercings or dental appliances. Or your hospital team may ask you to change into a hospital gown. Let the radiographer know if you’ve had a hip replacement or any spinal surgery.

Your DEXA scan will usually be done by a radiographer (a health professional trained to perform imaging procedures). When you arrive at the hospital, they’ll run through some questions with you. For example, they may check:

the names of any medicines you take
if you’ve had any other scans recently that involved contrast or nuclear medicine (because these can affect the results of your DEXA scan)
if there’s any possibility you may be pregnant
your height and weight

DEXA scan procedure

The scan itself will usually take between 10 and 20 minutes. But allow longer for your appointment because you may need other tests too.

Your radiographer will ask you to lie on your back on a padded table during the DEXA scan. You won’t be enclosed in any way (in a tunnel, for example). The X-ray machine will be underneath you. It sends out invisible beams of radiation, which pass through your bones to a detector that’s positioned above your body. The detector has a long, thin ‘arm’, which will pass up and down the area being tested – usually your hips or spine.

The detector will measure the amount of radiation it receives that has passed through your bones. This information is then used to generate images on a computer monitor, which show how dense your bone is.

It’s important to lie very still while you’re having the DEXA scan. Only change position if your radiographer asks you to.

Sometimes, you may have another scan called a vertebral fracture assessment (VFA). This is done in the same way as a DEXA scan but can check for fractures in your spine. It will take another 5 to 10 minutes.

DEXA scan results

A doctor trained to interpret X-ray images will analyse your DEXA scan results. They’ll send their findings in a report to your GP or the health professional who referred you for the bone density scan. Before you leave your appointment, the radiographer will usually tell you when to expect your results and how to get them. It will generally take a week or two.

You will get two numbers from your DEXA scan: a T-score and a Z-score.

T-score

The T-score compares your bone density to the average for a young, healthy person.

A T-score of between 0 and –1 means your bone density is in the normal range for a young, healthy person.
If your T-score is between –1 and –2.5, your bone density is slightly lower than normal for a young, healthy person. This is known as osteopenia.
A T-score below –2.5 is classed as osteoporosis.

Z-score

The Z-score compares your bone density with that of people your own age.

If you have a low Z-score, particularly if you’re young, it can indicate that there might be something that’s affecting your bone density levels. This might be another condition or medicine that you take.

After a DEXA scan

Your doctor will look at your DEXA scan results together with your fracture risk assessment to decide what to do next. They may ask you to have more tests to assess your bone health. These tests may include blood and urine tests and X-rays.

Osteoporosis treatment

If your DEXA scan results show you have osteoporosis, your doctor will prescribe you medicines. These will help slow down the rate at which you lose bone mass (density) and aim to increase your bone mass. We all lose bone mass as we get older but with osteoporosis, your body breaks down bone faster than it builds it up. Medicines can help to slow down bone loss and help to increase bone density.

Medicines can include bisphosphonates or other types of medicines. The medicine or medicines your doctor recommends will depend on the severity of your osteoporosis and your risk of fractures. Your doctor will usually offer you a review after three to five years to see if these medicines are working for you. You have another DEXA scan after this time, to see if your bone health has improved.

Lifestyle advice

You won’t need to take medicines if you’re diagnosed with osteopenia (unless you have a high fracture risk) or you’re not at risk of developing osteoporosis. But your doctor will suggest some lifestyle changes you can make to help slow down the loss of bone mass and strengthen your bones.

These may include the following.

Eat a healthy, balanced diet, that includes plenty of calcium. Foods high in calcium include milk, cheese, yoghurt, sardines and calcium-fortified breads and cereals.
Get enough vitamin D because this helps your body to absorb calcium. Try to get out in the sun for a short time on a regular basis but take care not to burn your skin. You can get limited amounts of vitamin D from the foods you eat, such as oily fish and egg yolks. Vitamin D supplements can help to boost your levels. The government advises that everyone in the UK should take a daily supplement containing 10 µg (micrograms) of vitamin D from October to March.
Keep active by doing some regular exercise – include daily weight-bearing exercise, such as walking, and some strength training at least two times a week.
If you smoke, try to stop because smoking increases the risk of fragility fractures.
If you drink alcohol, stick to the recommended limits.

Your hospital may ask you to come back for another DEXA scan within the next two years if your results showed you’re at risk of developing osteoporosis.

Risks for a DEXA scan

DEXA is a very safe procedure with no real risk of side-effects or complications.

The scan will expose you to some X-ray radiation. Radiation can be harmful to your body if you have a high dose. But the amount you’re exposed to in a DEXA scan is very low – much less than you’d get in other tests, such as a chest X-ray. But if you’re pregnant or think you might be, it's important to let your doctor or radiographer know. You might not be able to have a DEXA scan because there’s a risk that the radiation could harm your baby.

Alternatives to a DEXA scan

There are other scans and tests that can help to find out how strong your bones are. But they’re not as good at measuring bone-mineral density as a DEXA scan. Other tests include:

a CT scan – this can accurately measure low bone mass, but involves a higher level of radiation than a DEXA scan
an ultrasound scan – this uses sound waves to look at your bone structure and strength
a standard X-ray – this can show if you have any fractures and may reveal if you have weak bones (osteopenia)

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A DEXA scan can check the density of your bones to show how strong they are. It’s a test that doctors use to help diagnose osteoporosis.

For more information, see our section About DEXA scan.

No, a DEXA scan can’t show tumours. But if you have cancer, some treatments can cause your bones to get thinner and less dense (osteoporosis). Some treatments for breast cancer and prostate cancer can cause this, for example. So you might need to have a DEXA scan to check if this is happening to you. You can then get any treatment you might need.

For more information, see our section About DEXA scan.

There isn’t anything you need to do to prepare for a DEXA scan. You’ll have the scan and go home the same day. You may be able to keep your clothes on during the scan if you’re not wearing anything metal, but you might need to wear a hospital gown. Your hospital will check if you’ve had any other scans or surgery recently that may affect the results of your DEXA scan. They’ll also check if you’re pregnant because there’s a risk the radiation could harm your baby.

For more information, see our section on preparation for a DEXA scan.

Your doctor will usually recommend you have a DEXA scan as part of an assessment for osteoporosis at age 65 and older (for women) and 75 and over (for men). They may advise you have it sooner if you’re at risk of osteoporosis or if you’ve had fragility or stress fractures before.

For more information, see our section on assessment for a DEXA scan.

The scan is safe, quick and painless and usually takes between 10 and 20 minutes. You’ll lie on your back on a padded table during the scan. An X-ray machine underneath you will send beams of radiation which pass through your bones to a detector that’s positioned above your body.

For more information, see our section on DEXA scan procedure.

You may be able to keep your bra on but if it’s underwired you may need to take it off. Metal items can show up on the scan and blur the images so you may need to remove them. Ask your hospital for advice.

For more information, see our section on preparation for a DEXA scan.

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