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DXA scan (dual energy X-ray absorptiometry)

A dual energy X-ray absorptiometry (DXA or DEXA) scan measures your bone density. It can look for signs of fragile (brittle) bones to assess your risk of a fracture (break).

You will meet the radiographer carrying out your procedure to discuss your care. It may differ from what is described here as it will be designed to meet your individual needs.

A DXA scan uses X-ray equipment and a computer to measure the density of your bones.

A DXA scan projects X-rays onto your bones. Some of this radiation travels straight through your bones and a certain amount is absorbed by them. How much is absorbed depends on how dense your bones are. A device called a detector measures how much radiation passes through your bones and it sends the information to a computer. This works out an average bone density score. Your score will be compared with normal measurements for both a young, healthy adult, and to people your own age, size and gender. Low scores indicate that your bones are fragile and more likely to fracture.

Doctors use DXA scans to assess your risk of developing osteoporosis. This is a condition where your bones lose their density and become weak, brittle and more likely to fracture. Your doctor may advise you to have a DXA scan if you fracture a bone after only a minor bump or fall. You may also need to have a DXA scan if you’re at a high risk of osteoporosis. Doctors also use DXA scans to monitor how well you respond to treatment for osteoporosis.

You may need to have a DXA scan if you have another health condition that can affect the density of your bones. These include eating disorders, such as anorexia nervosa, and kidney disease.

A DXA scan is quick and painless, and both adults and children can have the scan.

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Details

  • Preparation Preparing for a DXA scan

    DXA scans are usually done as a hospital outpatient procedure in the imaging or radiology department.

    Your radiographer (a health professional trained to perform imaging procedures) will explain how to prepare for your scan.

    If you usually take any medicines, continue to take them unless your doctor or radiographer tells you not to. However, don't take calcium supplements for at least 24 hours before your scan.

    It's best to wear light clothing that doesn't have any metal fasteners. Your radiographer may ask you to remove any metal jewellery because this can interfere with the scan.

    Your radiographer will discuss with you what will happen before, during and after your scan. This is your opportunity to understand what will happen. You can help yourself by preparing questions to ask about the risks, benefits and any alternatives to the procedure. This will help you to be informed, so you can give your consent for the procedure to go ahead. You may be asked to sign a consent form.

  • Alternatives What are the alternatives to a DXA scan?

    Alternative imaging tests, such as an ultrasound, X-ray or CT scan, can assess your risk of a fracture. However, some of these tests aren't as reliable as DXA scans. Also, CT scans use a larger dose of radiation than DXA scans.

    Blood and urine tests can check the levels of chemicals, such as calcium, that are produced when your body breaks down and forms new bone. This can provide information about factors that might affect your bone strength but they can’t directly diagnose osteoporosis or bone strength.

  • The procedure What happens during a DXA scan?

    The scan will usually take between 10 and 20 minutes.

    Your radiographer may ask you to remove certain items of clothing or to wear a gown. You will lie on a padded table during the scan. Your radiographer may position different parts of your body to improve the images. For example, to assess your hip, he or she may put your foot in a brace that will rotate your hip inwards.

    Your radiographer will operate the scanner from behind a wall or an adjoining room. However, he or she will be able to see, hear and speak to you during the procedure.

    The X-ray machine will slowly pass over your body and send X-rays through the bones that your radiographer is testing. A detector will measure how much X-ray radiation passes through your bones and send this information to a computer. It’s important to lie very still as each bone is scanned. Your radiographer may ask you to hold your breath for a few seconds while he or she takes the X-ray picture. This will help to prevent a blurred image.
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  • Aftercare What to expect afterwards

    You will usually be able to go home when you feel ready.

    Your radiographer will send your scan to a radiologist, who will prepare a report. A radiologist is a doctor who specialises in using imaging methods to diagnose medical conditions. The report will then be forwarded to your GP. This can take several days. Before you go home, ask your radiographer when you can expect to get your results.

    Results of a DXA scan

    The results of the scan are given as a T-score. This is a measure of how your bone density compares with the normal average for young, healthy adults.

    • 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.

    If your T-score indicates that you may have osteopenia or osteoporosis, your GP will give you advice about treatment options. You may be referred to see a specialist, such as a rheumatologist. Your GP will consider both the T-score and other risk factors when he or she gives you advice about treatment to help prevent fractures.

    A DXA scan will also give you a Z-score. This compares your bone density with that of people your own age, size and gender. If your score is lower than the average, you may need to have further tests.

  • Risks What are the risks?

    As with every procedure, there are some risks associated with a DXA 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. However, the dose is very low and roughly a tenth of that used for a chest X-ray. It's one of the lowest doses of radiation used in medical procedures.

    If you’re pregnant

    If you’re pregnant, or think you might be, it's important to let your GP or radiographer know. You might not be able to have a DXA scan as there is a risk that the radiation could harm your unborn baby. However, it depends on why you need a scan. Ask your doctor or radiographer for advice.

  • FAQs FAQs

    I'm a 79-year-old woman and broke my wrist in a recent fall. Do I need to have a DXA scan?

    Answer

    You may need to have a DXA scan but speak to your GP. You may also need to start treatment to help prevent any further breaks (fractures).

    Explanation

    DXA scans can help doctors to spot people who are at high risk of developing osteoporosis and who could benefit from treatment to prevent fractures.

    If you're over 65 (particularly if you're a woman), you already have a greater risk of getting osteoporosis than when you were younger. Having had a wrist fracture also may suggest that you have fragile bones.

    Speak to your GP for advice and information about starting treatment to help prevent fractures.

    What will happen if I'm classed as having osteopenia?

    Answer

    If you have a DXA scan and are diagnosed with osteopenia, your GP is likely to advise you to make some changes to your lifestyle.

    Explanation

    Having osteopenia means you have a lower bone density than normal and could be at risk of developing osteoporosis. If you get a diagnosis of osteopenia after your DXA scan, your GP will probably suggest you make some changes to your lifestyle. These can help to slow down the possible progression to osteoporosis and therefore reduce your risk of fracturing a bone. Your GP may recommend the following lifestyle changes.

    • Include more calcium in your diet. Foods high in calcium include milk, cheese, yoghurt, sardines and green vegetables such as broccoli and cabbage. Your doctor may advise you to take vitamin D supplements too as they help your body to absorb calcium.
    • Carry out regular, low-impact, weight-bearing exercise, such as walking.
    • If you smoke, try to stop.
    • Drink alcohol in moderation. Stick to the recommended daily limits set by the Department of Health. This is no more than two to three units a day for women, and three to four units a day for men.

    Your doctor won't usually prescribe you any medicines if your bone density isn't low enough for you to be diagnosed with osteoporosis. However, you may need to have another DXA scan two to five years later to check if your bones have lost more density.

    Will a scan on my heel show whether I have osteoporosis?

    Answer

    A DXA scan of your heel can help to predict if you will have a fracture (break) but they aren't usually used to diagnose osteoporosis. This is because the bone density in your heel isn't always a good indication of the density in your other bones. A scan of your hip and spine is considered the 'gold standard' for diagnosing osteoporosis.

    Explanation

    A scan of your hip and spine is considered to be the most reliable method to diagnose osteoporosis and to predict the risk of fractures. This is partly because international statistics that enable your risk of fractures to be worked out are based on scans of these bones. Also, a fractured hip is one of the most serious consequences of osteoporosis. The best way to predict it is to scan the hip rather than any other bone.

    Alternative scanners are available that can measure the bone density of your heel and other bones including those in your forearm, finger and hand. These are known as peripheral scans and are sometimes used in screening to see whether you may need further investigations.

    If you have a peripheral scan that shows you have a low bone density, you're likely to need a hip and spine DXA. This will confirm the findings.

    Will I have a repeat DXA scan to check if my treatment for osteoporosis is working?

    Answer

    You will usually only need to have another scan if you fracture a bone after a minor bump or fall.

    Explanation

    If you haven't broken any bones while taking a treatment for osteoporosis, it's thought to be enough evidence that your treatment is working well. It's not usually necessary to have another DXA scan just to check up on your progress.

    If you do fracture (break) a bone while taking a treatment for osteoporosis, your GP may refer you to see a specialist. You might need to have another scan. However, you won't usually have a repeat scan unless you have been on treatment for at least two years (less if you take steroids). This is because it can take up to two years for the treatment to have a beneficial effect on your bones.

    If a repeat scan shows that your bone density is still below normal, you might need to try another type of treatment.

  • Resources Resources

    Further information


    Sources

    • ACR-SPR-SSR practice guideline for the performance of dual-energy X-ray absorptiometry (DXA). American College of Radiology. www.acr.org, published 2013
    • Bone densitometry. Radiological Society of North America. www.radiologyinfo.org, published 22 April 2013
    • Guideline for the diagnosis and management of osteoporosis in postmenopausal women and men from the age of 50 years in the UK. National Osteoporosis Guideline Group. www.shef.ac.uk, published May 2013
    • Osteoporosis: fragility fracture risk. National Institute for Health and Care Excellence (NICE), August 2012. www.nice.org.uk
    • Scans and tests and osteoporosis. National Osteoporosis Society. www.nos.org.uk, published August 2013
    • Osteoporosis. Medscape. www.emedicine.medscape.com, published 4 October 2013
    • ACR appropriateness criteria. American College of Radiology. www.acr.org, published 2010
    • Having a bone density test. National Osteoporosis Foundation. www.nof.org, accessed 4 December 2013
    • Clinician’s guide to prevention and treatment of osteoporosis. National Osteoporosis Foundation. www.nof.org, published 2013
    • ACR-SPR practice guideline for imaging pregnant or potentially pregnant adolescents and women with ionizing radiation. American College of Radiology. www.acr.org, published 2013
    • Osteoporosis management. Map of Medicine. www.mapofmedicine.com, published 16 October 2013
    • Calcium. Food Standards Agency. www.eatwellscotland.org, accessed 5 December 2013
    • Rizzoli R, Boonen S, Brandi ML, et al. Vitamin D supplementation in elderly or postmenopausal women: a 2013 update of the 2008 recommendations from the European Society for Clinical and Economics Aspects of Osteoporosis and Osteoarthritis. Curr Med Res Opin 2013; 29(4):1–9. doi:10.1185/03007995.2013.766162
    • Alcohol labelling. Department of Health. www.dh.gov.uk, published 3 February 2012
    • Osteoporosis – prevention of fragility fractures. NICE Clinical Knowledge Summaries. cks.nice.org.uk, published September 2013
    • Patients. International Society for Clinical Densitometry. www.iscd.org, published 25 November 2013
    • 2013 ISCD official positions – adult. International Society for Clinical Densitometry. www.iscd.org, published 15 August 2013
    • Calculation tool. World Health Organization Collaborating Centre for Metabolic Bone Diseases. www.shef.ac.uk, accessed 5 December 2013
    • Welcome to the QFracture-2012 risk calculator. QFracture. www.qfracture.org/index.php, published 2012
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