DEXA Bone Density

If you are pregnant, or think you may be pregnant, or are breastfeeding, please be sure to let your technician know PRIOR to undergoing any radiology procedure.

What is a DEXA scan and what does it measure?

DEXA stands for “dual emission x-ray absorptiometry”. It is a test that measures the density of bones. In general, the more dense the bone, the stronger it is, and the less likely it is to break. The DEXA is also capable of calculating body mass fat/muscle percentages.

How does a DEXA scan work?

A DEXA scan uses low energy x-rays. (The dose of radiation used is less than a normal x-ray test.) A machine sends x-rays from two different sources through the bone being tested. Bone blocks a certain amount of the x-rays. The more dense the bone is, the less x-rays get through to the detector. By using two different x-ray sources rather than one it greatly improves the accuracy measuring the bone density.

The amount of x-rays that comes through the bone from each of the two x-ray sources is measured by a detector. This information is sent to a computer which displays the bone’s density as an image, and calculates a score of the average density of the bone. A low score indicates that the bone is less dense than it should be “thin” and is more prone to fracture if you have an injury.

How is a DEXA scan performed?

You lie on your back on a pad and are asked to keep still while an x-ray detector (the scanner) comes over the area to be tested. An x-ray machine under the couch fires x-rays towards the detector. The bones commonly scanned are the vertebra (back bones), hip and wrist. (These are the bones most commonly affected by osteoporosis.) The scan is painless and takes 10-15 minutes. You do not need to do any special preparation prior to a DEXA scan.

Who should have a DEXA scan?

A DEXA scan may be advised if you are at increased risk of developing osteoporosis. Osteoporosis usually causes no symptoms at first. But, if you have osteoporosis, you have an increased risk of breaking a bone after an injury. If a DEXA scan shows that you have osteoporosis, then you may be given advice and treatment to help strengthen your bones. Therefore, a DEXA scan may be advised if you have:

  • A fracture following a minor fall or injury.
  • Loss of height due to fracture of a vertebra (back bone).
  • Taken steroid tablets for three months or more.
  • An early menopause (aged less than 45).
  • A history of periods stopping (amenorrhoea) for more than one year.
  • Other disorders associated with osteoporosis. (i.e. rheumatoid arthritis).
  • A family history of hip fracture on your mothers side.
  • A body mass index of less than 18.5. (That is, if you are very underweight.)
    BMI Calculator

The National Osteoporosis Foundation (NOF) recommends bone density testing for all women over age 65. The NOF also recommends bone density testing for all women under the age of 65 who have one or more risk factors for osteoporosis, not a bone density test is a simple and painless way to help your doctor measure the health of your bones. It may also be used to monitor your rate of bone loss and response to therapy.

Early on, osteoporosis is a silent disease, so you may not see any signs. However, it can eventually lead to broken bones or the disfiguring “dowager’s hump.” The good news is, if osteoporosis is detected early enough, its effects may be prevented.