Bone densitometry scan - When a DEXA (DXA) scan is used

DEXA (DXA) scans are used to measure bone density and assess the risk of bone fractures.

They're often used to help diagnose bone-related conditions such as osteoporosis (or the risk of developing it).

Total body DEXA scans can also be used to measure body composition (the amount of bone, fat and muscle in the body). This type of scan is routinely used in children, but is still a research application in adults.

Identifying bone conditions

Unlike ordinary X-ray images, DEXA scans can measure very small reductions in bone mineral density. This makes it possible to diagnose osteoporosis in its early stages before fractures occur.

A DEXA scan also uses a low dose of radiation, which means the risks to health are much lower than standard X-rays.

Doctors use the results of DEXA scans to help them decide whether treatment for low bone mineral density is needed.

This may include making lifestyle changes to help improve your bone health, such as:

• eating a healthy, balanced diet that's high in calcium
• spending more time in the sun to help increase your levels of vitamin D
• regularly doing weight-bearing exercise, such as walking or running

When a DEXA scan is recommended

A DEXA scan may be recommended if you have an increased risk of developing a bone condition such as osteoporosis. Your risk is increased if you:

• have had a fracture after a minor fall or injury
• are a woman who has had an early menopause, or you've had your ovaries removed at a young age (before 45) and haven't had hormone replacement therapy (HRT)
• are a post-menopausal woman and you smoke or drink heavily, have a family history of hip fractures or you have a body mass index (BMI) of less than 21
• are a man or a woman with a condition that leads to low bone density, such as rheumatoid arthritis   
• are a woman who has large gaps between periods (more than a year)
• are a man or a woman taking oral glucocorticoids for three months or more (glucocorticoids are used to help treat inflammation, but can also cause weakened bones)

Limitations

A DEXA scan isn't the only way of measuring bone strength or fragility. Other risk factors need to be taken into consideration, such as family history and medication use, to determine who's at risk of developing bone fractures.

All of the risk factors will need to be considered before a DEXA scan is recommended and before any treatment is started.

Some people will need to have a DEXA scan to confirm that their risk of developing bone fractures is high enough to need treatment. For others, particularly the elderly, the risk of fracture may be so high that there's no need for them to have a DEXA scan before treatment is prescribed.

Interpreting the results of a DEXA scan can sometimes be difficult. For example, it may not be easy to interpret the results of a scan of the spine when someone has a degenerative condition, such as osteoarthritis. Sometimes, spinal abnormalities or a previous spinal fracture can give a false result.

A DEXA scan won't show whether low bone mineral density is due to osteoporosis (too little bone) or osteomalacia (too little calcium in bone, usually due to a lack of vitamin D).