Bone Density (DEXA)
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:
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.
