 Bone
density scanning, also called dual-energy x-ray
absorptiometry (DXA or DEXA) or bone densitometry,
is an enhanced form of x-ray technology that is
used to measure bone loss. DEXA is today's established
standard for measuring bone mineral density (BMD).
DEXA stands for "dual-energy x-ray absorptiometry,"
and is considered the most accurate test for bone
density. While standard x-rays show changes in bone
density after about 40% of bone loss, a DEXA scan
can detect changes after about a 1% change. A DEXA
scan lasts about 10 minutes, and exposes the patient
to less radiation than a standard chest x-ray (about
the same amount of radiation exposure as taking
a trans-continental flight).
An x-ray (radiograph) is a painless medical test
that helps physicians diagnose and treat medical
conditions. Radiography involves exposing a part
of the body to a small dose of ionizing radiation
to produce pictures of the inside of the body. X-rays
are the oldest and most frequently used form of
medical imaging.
DEXA is most often performed on the lower spine
and hips.
DEXA bone densitometry is most often used to diagnose
osteoporosis, a condition that often affects women
after menopause but may also be found in men. Osteoporosis
involves a gradual loss of calcium, causing the
bones to become thinner, more fragile and more likely
to break.
DEXA is also effective in tracking the effects of
treatment for osteoporosis and other conditions
that cause bone loss.
The DEXA test can also assess an individual’s
risk for developing fractures.
Bone density testing is strongly recommended if
you:
- are
a post-menopausal woman and not taking
estrogen.
- have
a personal or maternal history of hip
fracture or smoking.
- are
a post-menopausal woman who is tall (over
5 feet 7 inches) or thin (less than 125
pounds).
- are
a man with clinical conditions associated
with bone loss.
- use
medications that are known to cause bone
loss, including corticosteroids such as
Prednisone, various anti-seizure medications
such as Dilantin and certain barbiturates,
or high-dose thyroid replacement drugs.
-
have type 1 (formerly called juvenile
or insulin-dependent) diabetes, liver
disease, kidney disease or a family history
of osteoporosis.
-
have high bone turnover, which shows up
in the form of excessive collagen in urine
samples.
- have
a thyroid condition, such as hyperthyroidism.
- have
experienced a fracture after only mild
trauma.
- have
had x-ray evidence of vertebral fracture
or other signs of osteoporosis.
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How
does the procedure work?
The DEXA machine sends a thin, invisible beam
of low-dose x-rays with two distinct energy peaks
through the bones being examined. One peak is
absorbed mainly by soft tissue and the other by
bone. The soft tissue amount can be subtracted
from the total and what remains is a patient's
bone mineral density.
DEXA machines feature special software that compute
and display the bone density measurements on a
computer monitor.
Benefits
- DEXA
bone densitometry is a simple, quick and
non-invasive procedure.
- No
anesthesia is required.
- The
amount of radiation used is extremely
small—less than one-tenth the dose
of a standard chest x-ray.
-
DEXA bone density testing is the most
accurate method available for the diagnosis
of osteoporosis and is also considered
an accurate estimator of fracture risk.
- DEXA
equipment is widely available making DEXA
bone densitometry testing convenient for
patients and physicians alike.
- No
radiation remains in a patient's body
after an x-ray examination.
- X-rays
usually have no side effects.
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The
only sure way to determine bone density and fracture
risk for osteoporosis
is to have a bone mass measurement (also called
bone mineral density or BMD test).
Your doctor can help you determine whether you should
have a BMD test. NOF Guidelines indicate, BMD testing
should be performed on:
•
All women aged 65 and older regardless of
risk factors*
• Younger postmenopausal women with
one or more risk factors (other than being
white, postmenopausal and female).
• Postmenopausal women who present with
fractures (to confirm the diagnosis and determine
disease severity). |
*Note: Medicare covers BMD testing for the
following individuals aged 65 and older:
•
Estrogen deficient women at clinical risk
for osteoporosis
• Individuals with vertebral abnormalities
• Individuals receiving, or planning
to receive, long-term glucocorticoid (steroid)
therapy
• Individuals with primary hyperparathyroidism
• Individuals being monitored to assess
the response or efficacy of an approved osteoporosis
drug therapy. |
Medicare permits individuals to repeat BMD testing
every two years.
There are several ways to measure bone mineral density;
all are painless, noninvasive and safe and are becoming
more readily available. In many testing centers
you don't even have to change into an examination
robe.
The tests measure bone density in your spine, hip
and/or wrist, the most common sites of fractures
due to osteoporosis. Recently, bone density tests
have been approved by the FDA that measure bone
density in the middle finger and the heel or shinbone.
Your bone density is compared to two standards,
or norms, known as "age matched" and "young
normal." The age-matched reading compares your
bone density to what is expected in someone of your
age, sex and size. The young normal reading compares
your density to the optimal peak bone density of
a healthy young adult of the same sex.
The information from a bone density test enables
your doctor to identify where you stand within ranges
of normal and to determine whether you are at risk
for fracture. In general, the lower your bone density,
the higher your risk for fracture. Test results
will help you and your doctor decide the best course
of action for your bone health.
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