DEXA (dual energy X-ray absorptiometry) scan

Expert reviewer, Mr Roger M Tillman, Consultant Orthopaedic Surgeon
Next review due December 2019

A DEXA (dual energy X-ray absorptiometry) scan measures the density of your bones and how strong they are. You may have one as part of checks for low bone-mineral density – a condition that makes bones more fragile.

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About DEXA scan

Your doctor may suggest a DEXA scan if you’re at particular risk of developing osteoporosis. This is a condition where your bones lose their density and become weak, brittle and more likely to fracture (break). This sort of fracture is called a fragility fracture.

DEXA scans can also help spot osteopenia, a similar but less severe condition, which can develop into osteoporosis over time.

Your doctor may recommend a DEXA scan if you fracture a bone after a minor bump, fall or during an everyday activity, like bending over. They may think your bone density should be checked because you’re at increased risk of osteoporosis because of your age or medical history. Becoming more stooped and losing height are signs of fragile bones.

DEXA scans use X-ray equipment but at very low levels of radiation. They are safe, quick and painless.

A DEXA scan projects X-rays onto your bones, usually in your hip and spine for the best results. It detects how much radiation is absorbed by your bones, which shows how dense they are.

A DEXA scan will normally be carried out at hospital. The procedure may vary depending on your local area and individual needs. Your doctor will explain this to you.

Assessing whether you need a DEXA scan

Your doctor will usually consider how much you’re at risk of fragility fractures before suggesting a DEXA scan, especially if you’re under 50. There are two special online tools that doctors use to calculate this, called FRAX® and QFracture®.

These tools take into account things like your own and your family’s health, your age, height and weight and any medication you’re on. Your lifestyle is important too. Things like smoking, alcohol and lack of physical activity can affect bone density.

The tools then predict how likely it is you’ll develop osteoporosis and fragile bones in the next 10 years. They produce a red (high risk), amber or green (low risk) rating that helps your doctor decide what action to take. You may have a health condition that increases the risk, including:

  • diabetes
  • liver disease
  • respiratory (breathing) problems
  • gastric (stomach) problems
  • eating disorders, such as anorexia nervosa
  • kidney disease
  • blood disorders
  • rheumatology problems like arthritis

Some medication adds to the risk, particularly corticosteroids. Other strong risk factors include the menopause (especially in younger women), and being underweight.

Your doctor may suggest a DEXA scan without first calculating your risk if you’re over a certain age, or have already broken a bone from a minor bump or fall.

Preparing for a DEXA scan

You may have to wait for a month or so before you get an appointment for a DEXA scan. They are usually done as a hospital outpatient procedure in the imaging or radiology department. Arrangements for scans, and how they’re carried out, may vary between hospitals, so you should follow individual instructions.

The scan will be done by a radiographer – a health professional trained to perform imaging procedures. They will explain the procedure. You don’t usually need to make special preparations for a DEXA scan.

Do tell your doctor if you’ve recently had another sort of X-ray, especially if it involved swallowing or being injected with something to show up on the image. For example, you may have had a ‘barium meal’. You may need to wait for a couple of weeks before having a DEXA scan.

You may be able to stay fully dressed during the scan. But make sure you’re not wearing anything that could show up on the image of the area being scanned, like buttons, zips or jewellery. You may have to take everything out your pockets and remove any metal body piercings.

Alternatives to a DEXA scan

A DEXA scan uses X-rays with two different energies. The X-rays pass through the bone being tested to measure its density as accurately as possible.

There are other tests to check how strong your bones are, but they’re not as good at measuring bone-mineral density. For example, a CT scan also uses X-rays to collect images but with higher levels of radiation and less accurate results. An ultrasound uses sound waves to look at bone structure and strength, but you may need a DEXA scan as well. A standard X-ray can check for fractures but can’t show signs of osteoporosis until it’s very advanced.

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What happens during a DEXA scan

The scan will usually take between five and 20 minutes.

You will lie on your back on a padded table during the scan. Unlike some other types of scan, you won’t be enclosed in any way (in a tunnel, for example).

An X-ray machine sends X-rays from two sources through your bones to a detector. This is a thin metal arm that moves up and down over the area being tested, usually your hips or spine.

A DEXA scan of your hip and spine is considered to be the ‘gold standard’ for diagnosing osteoporosis and predicting future fracture risk. This is partly because a fractured hip is one of the most serious consequences of osteoporosis.

The detector measures the amount of radiation that comes through the bone and sends this information to a computer. This shows how dense the bone is.

It’s important to lie very still as each bone is scanned. This ensures the scan produces clear images.

Because DEXA scans use a very low level of radiation, it’s safe for the person doing the scan to stay in the room with you. They may position your body in a certain way to get the best possible image.

What to expect afterwards

A radiologist specially trained to interpret X-ray images will analyse the results. They’ll send their findings in a report to your GP or the doctor who referred you for the scan. Your doctor will discuss the results with you.

Results of a DEXA scan

The results are given as two scores based on your variation from the population average: a T-score and a Z-score.

  • A T-score of between 0 and –1 means your bone density is normal.
  • If your T-score is between –1 and –2.5, you’re classed as having osteopenia. This means your bone density is lower than normal, but you don't yet have osteoporosis.
  • A T-score below –2.5 is classed as osteoporosis.

The Z-score compares your bone density with that of people your own age, weight and sex.

If your scores are low, especially if they indicate that you may already have osteopenia or osteoporosis, your GP will explain possible actions. These may include treatment, lifestyle changes to strengthen your bones or seeing a specialist.

Your doctor may refer you for further tests to see if an underlying health condition is affecting your bone strength. These tests are usually on your blood and urine. They look at your thyroid and kidney functions, your levels of calcium and phosphorus, vitamin D, and testosterone (in men), and a protein called albumin.

General lifestyle advice

If you are diagnosed with osteopenia or at risk of developing osteoporosis, your GP may suggest some lifestyle changes to strengthen your bones.

Smoking, drinking too much alcohol, vitamin D deficiency, calcium deficiency, and lack of activity all increase the risk of osteoporosis. So your GP may recommend the following.

  • Eat a healthy, balanced diet, including plenty of calcium. Foods high in calcium include milk, cheese, yoghurt, sardines and green vegetables like spinach.
  • Get enough vitamin D – it helps your body absorb calcium. If possible, expose your skin to the Sun for 15 minutes several times a week. Include foods like oily fish, eggs and fortified cereals in your diet because these are sources of vitamin D.
  • Do some weight-bearing exercise, such as walking, every day.
  • If you smoke, try to stop.
  • Drink alcohol in moderation. Stay within the government guidelines of no more than 14 units a week.

Your doctor may advise you to take calcium or vitamin D supplements if you cannot get enough of these from your diet. These may be helpful if you’re older, especially if you’re housebound or in residential care. This is because ageing makes it harder to absorb calcium and vitamin D. If you’re pregnant or breastfeeding, you may need extra calcium.

Repeat DEXA scans

You won’t usually have another scan for at least two years. Your doctor may then want to do a further check if your earlier results showed you were at risk of developing osteoporosis.

They may also suggest a repeat scan if you’ve had a fragility fracture – breaking a bone after a minor bump or fall. If you’ve started certain medication, particularly steroids, a scan can check if it’s affecting your bone strength.

You don’t need to keep having scans just to monitor changes in bone density. Your doctor will consider other factors. These include developing a medical condition that increases the risk of osteoarthritis, or if you’ve just been through menopause. But you should have another scan within five years.

If you’ve begun treatment for osteoporosis, it can take two years for this to have a real impact that shows up on a DEXA scan. A common medication, bisphosphonates, may be reviewed after five years of taking it. After two to five years, your doctor may suggest a repeat scan if they think another treatment might work better for you.  

If you do have a repeat scan, ideally it should be carried out using the same machine, for accurate comparison.

Risks of a DEXA scan

As with every procedure, there are some risks associated with a DEXA scan. We haven't included the chance of these happening as they are specific to you and differ for every person. Ask your doctor or radiographer to explain how these risks apply to you.

During the scan you will be exposed to some X-ray radiation, but at a very low dose that is close to natural daily radiation levels.

If you’re pregnant

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 as there is a risk that the radiation could harm your unborn baby.

Frequently asked questions

  • If you're over 65 (particularly if you’re a woman), you’re already at more risk of getting osteoporosis than when you were younger. A wrist fracture may suggest that you have fragile bones.

    Having had a broken wrist, you should speak to your doctor about having a DEXA scan to assess your risk of further fractures. Your doctor may suggest a scan using a peripheral DEXA device. This is a smaller machine that can measure bone density on the periphery of your skeleton, including your wrist. It will give a better idea of whether a full DEXA scan or other tests are necessary.

    Your doctor also advise changes to your diet and lifestyle, as well starting medication, to strengthen your bones and help prevent any further breaks.

  • It depends on your particular circumstances. You may be already seeing a hospital consultant if you’ve had a broken bone, or are attending a fracture clinic. They may suggest a DEXA scan to check how fragile your bones are.

    DEXA scans are carried out at both NHS and private hospitals. Arrangements will vary at different hospitals and in different areas.

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  • Reviewed by Natalie Heaton, Specialist Editor, Bupa Health Content Team, December 2016
    Expert reviewer, Mr Roger M Tillman, Consultant Orthopaedic Surgeon
    Next review due December 2019

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