DEXA bone density scan

The scan is used to:

• Find out whether bone strength has been lost, as happens in osteoporosis
• Judge the chance of a break in the years ahead, together with your other risk factors
• Help decide if the bones need a protecting treatment
• Track the bones over the years, and what any treatment is doing for them

Little needs organising, but a few points help the scan go smoothly:

• Clothing. Choose clothes that are not bulky around the waist or hips, without metal zips, buttons, clasps, buckles or an underwired bra, which show on the pictures. Depending on the area scanned, you may be able to stay in your own clothes, or you may be given a gown.
• Supplements and medicines. Some units ask you not to take calcium supplements for the 24 hours before the scan, since a tablet still in the gut can upset the reading at the spine. Prescribed medicines can usually be taken as on any other day, and the unit can tell you if in doubt.
• Recent tests. If you have had a barium study, a nuclear medicine scan, or an X-ray with an injection of dye in the two weeks before the scan, let the unit know before the day, whether at booking or after it, as it may suggest a short wait so that the earlier test does not affect the result.
• Pregnancy. The dose of radiation is very low, but the scan is not advised in pregnancy. Tell the unit if there is any chance you are pregnant.

The scan itself is simple. You lie on your back on the scanning table while an arm of the scanner passes slowly over you, usually measuring the lower spine and one hip, and sometimes the wrist; your legs may rest on a foam block for the spine, and a foot be angled slightly inwards so that the hip shows clearly. You need to keep still while it does so. There is no tunnel and no injection, it usually takes 10 to 20 minutes, and you may be able to stay dressed. Some units also make a vertebral fracture assessment on the same machine, to look for breaks in the spine that may have caused no symptoms, and you may lie on your side for it.

Your result is expressed as a score, a comparison between your bone density and the value expected. Its meaning comes from reading it together with your age, your past health and the other things that make a break more or less likely.

Dr Borukhson arranges DEXA scans where they will help, as part of a wider assessment of bone health, and explains what the result means for you and what, if anything, to do about it. The osteoporosis page says more.

A DEXA scan can be arranged through your GP too. Seeing Dr Borukhson, though, often means the scan is arranged more quickly and the result is read by a rheumatologist, who can act on it within the same assessment of your bones.

Once the scan is done you can go home and carry on with your day.

The pictures and measurements are looked at and reported, so you are not usually told the result at the scan itself; it goes to whoever referred you, often within about three weeks. It is commonly read alongside a fracture-risk calculator such as FRAX or QFracture; FRAX, the one that can take a scan result, weighs your age, past breaks, a parent's broken hip, steroid use, whether you smoke and how much alcohol you drink.

What comes next depends on what the scan finds. If the result is reassuring, the next step may be no more than a sensible wait before any further scan. If bone strength is reduced, the talk turns to protecting the bones, which can mean changes to exercise and diet, making sure you have enough calcium and vitamin D, and deciding whether a bone-protecting medicine is the right step for you. For anyone taking, or about to begin, long-term steroid treatment, the result helps decide, together with the dose, any earlier breaks and your other risk factors, whether bone protection should go with the steroids. The understanding your DEXA results page explains the scores, and the osteoporosis page covers treatment; if the scan shows osteoporosis, the warning signs to act on before your next review, and where to take each, are set out under When to seek help in that guide. If you cannot tell how urgent something is, asking is never a mistake.

Is the scan safe, and what dose of radiation does it carry?

It is very safe. The dose of radiation is very low, about what everyone is exposed to from natural surroundings over three days, and far less than most other X-rays. The scan does not hurt, you may be able to keep your clothes on, and you can go home straight afterwards. Pregnancy is the main reason to put it off, so tell the scanning unit if you could be pregnant.

What should I do to get ready for a DEXA scan?

Very little. Meals and drinks need no change. Wear clothes with no metal zips, buttons or clasps anywhere between the chest and the knees, since metal shows up on the pictures. Some units ask you to leave out calcium supplements for the 24 hours before the scan, because a tablet not yet dissolved in the gut can upset the reading at the spine. If you have had a barium study, a nuclear medicine scan, or an X-ray with an injection of dye in the two weeks before your scan, tell the unit before the day, since it may suggest waiting a little.

How are the T-score and the Z-score different?

Each measures your bone density against a reference. The T-score sets it against a healthy young adult and is the score used to look for osteoporosis; the Z-score sets it against people of your own age. A score is one input among several: what counts is the reading placed beside your age, your medical history and anything else that raises your risk, which together give a full sense of your bone health and your chance of a break.

When should the scan be repeated?

It varies. A second scan is not usually needed within two years, because bone changes slowly and a repeat scan within that time seldom shows a meaningful change, and many people wait between two and five years. How long to wait is set by your first result, how likely a break is, any change in your health and whether you are being treated. When scans are used to follow treatment, they are best done at the same hospital and on the same machine, so that any change is measured fairly.

Is a referral needed, or can a DEXA scan be arranged privately?

Your GP can arrange a scan, and a rheumatologist can too. Seeing Dr Borukhson often means the scan is booked more quickly and that a specialist reviews the result and acts on it, as one part of a full assessment of your bone health.