DXA (Dual X-ray
Absorptiometry) scans are used for determining
bone density and thus for diagnosis bone conditions such as
osteoporosis and
osteopenia. The work in much the same way as traditional X-rays – you lay under machine while it scans you. The process is quick, taking around 3 minutes, and completely painless. In fact it’s safer than even low-dose X-rays as less radiation is involved. (DXA was formerly referred to as DEXA.)
Who Will Be Scanned? If you are sent for a DXA scan, it is likely that you will be in one of the following at risk groups:
Post-menopausal women (whether naturally post-menopausal – having gone through “the change” – or surgically, having had a
hysterectomy) –
hormonal changes reduce the protection your
body gives to your bones
Long-term steroid users – people who have had long-term exposure to oral
corticosteroids such as Prednisolone (typically chronic
asthmatics and
emphysemics) tend to lose bone density
Ballet dancers (we had a lot of referrals from Birmingham Royal Ballet when I worked in Bone Densitometry) – partly due to the stress their exercises put onto their bones, and partly due to dietary concerns
People who suffer from eating disorders such as
anorexia nervosa People with a history of bone fractures
People with a family history of
osteoporosis (Women have a higher risk of osteoporosis and osteopenia due to
endocrine reasons, especially lower
testosterone levels. It’s highest instance is in women over 65.)
Evidence of
low bone density may also come from machines that measure the bone density in your foot (though some professionals question the value of this type of scan), or evidence may be seen on an X-ray. If so your doctor will probably refer you for a DXA scan.
How is your bone density determined? Unless a special request for a full body
scan has been made (or in some cases with children), the scan area is your hips and lower back area. This is because the signs of osteoporosis appear there first, so there’s no need to scan the whole body. As mentioned above, the process is quick and painless. The scan results will be reported by a radiologist.
For crucial points in your skeletal structure –
vertebrae L1, L2 etc and both femoral necks – the scan will produce a “T score” and a “Z score”. 1.0 is the average figure for a T
score with a normal range within a certain distance of that average at either side. The Z score is adjusted for age, as your bone density tends to go down as you get older. If your bone density is too low (or, rarely, too high) you may be seen by an additional bone expert (an endocrinologist with a special interest in metabolic bone disorders). The most basic treatment for prevention of bone mineral density loss is calcium and vitamin D
supplementation, while other drugs such as
Bisphosphonates (Alendronate, Risedronate, etc) may also be prescribed with a particular view to prevention of fractures.
That’s really all you need to know if you’re going to have a DXA scan, though normally the hospital will send you an information leaflet before your scan. It’s quick, painless, you don’t need to fast for it, and you can even have this scan if you’re pregnant or in a cast (unless it’s a whole body or possibly above knee cast). It really is one of the simplest, safest types of imaging you could possibly have. So if you were worried… don’t be!
More abstracts about the DXA scans