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Osteoporosis health centre

Bone densitometry scan - Introduction

NHS Choices Medical Reference

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A DEXA scan is a special type of

X-ray

that measures bone density. DEXA stands for dual energy X-ray absorptiometry.

DEXA scans, also known as DXA scans, bone density scans or bone densitometry scans are most commonly used to diagnose osteoporosis (where the bones become weak and fragile and more likely to break). They can also be used to assess the risk of osteoporosis developing.

A DEXA bone scan can also help detect other bone-related conditions, such as osteopenia (very low bone mineral density) and osteomalacia (softening of the bones caused by a vitamin D deficiency). In children, osteomalacia is known as rickets.

Osteoporosis

You may need to have a DEXA scan if you are at risk of developing osteoporosis.

Osteoporosis can affect people of both sexes and all ages, although older, post-menopausal women are particularly at risk. This is because after the menopause the level of the hormone oestrogen falls, resulting in a decrease in bone density.

The denser your bones, the stronger and less likely they are to fracture (break). Osteoporosis does not cause any symptoms until a bone is broken.

In the past it was difficult to measure bone density and identify those at risk of developing osteoporosis, until a fracture occurred.

However, by using bone densitometry techniques, such as bone density scans, it is now possible to measure bone density before fractures occur.

Read more about when DEXA scans are used.

Measuring bone density

During a DEXA scan, X-rays will be passed through your body. Some radiation will be absorbed by the bone and soft tissue, and some will travel through your body.

Special detectors in the DEXA scanner measure how much radiation passes through your bones and this information is sent to a computer.

The measurements will be compared to the normal range for bone density in a healthy adult and someone of the same gender and ethnicity.

Read more about how DEXA scans are carried out.

Safety

A DEXA scan is a quick and painless bone scan and is more effective than a normal X-ray in identifying low bone density. It also uses a much lower level of radiation than a standard X-ray.

A DEXA scan uses the equivalent of less than 10% of one day's exposure to natural background radiation. By comparison, a chest X-ray uses the equivalent of about five days' exposure to natural background radiation.

Despite being very safe procedures, DEXA scans and X-rays are not recommended for women who are pregnant. X-rays are not considered to be safe to use during pregnancy because they can cause damage to an unborn child.

Read more about your health during pregnancy.

Medical Review: December 19, 2011
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