Bone Density Test
What is a bone density test?
A bone density test is used to measure bone mineral content and density. It may be
done using X-rays, dual-energy X-ray absorptiometry (DEXA or DXA), or a special CT
scan that uses computer software to determine bone density of the hip or spine. For
various reasons, the DEXA scan is considered the "gold standard" or most accurate
This measurement tells the healthcare provider whether there is decreased bone mass.
This is a condition in which bones are more brittle and prone to break or fracture
A bone density test is used mainly to diagnose osteopenia and osteoporosis. It is
also used to determine your future fracture risk. The testing procedure typically
measures the bone density of the bones of the spine, lower arm, and hip. Portable
testing may use the radius (1 of the 2 bones of the lower arm), wrist, fingers, or
heel for testing, but is not as precise as the nonportable methods because only one
bone site is tested.
Standard X-rays may show weakened bones. But at the point when bone weakness can be
seen on standard X-rays, it may be too far advanced to treat. Bone densitometry testing
can find decreasing bone density and strength at a much earlier stage when treatment
can be beneficial.
Bone density test results
A bone density test determines the bone mineral density (BMD). Your BMD is compared
to 2 norms—healthy young adults (your T-score) and age-matched adults (your Z-score).
First, your BMD result is compared with the BMD results from healthy 25- to 35-year-old
adults of your same sex and ethnicity. The standard deviation (SD) is the difference
between your BMD and that of the healthy young adults. This result is your T-score.
Positive T-scores indicate the bone is stronger than normal; negative T-scores indicate
the bone is weaker than normal.
According to the World Health Organization, osteoporosis is defined based on the following
bone density levels:
- A T-score within 1 SD (+1 or -1) of the young adult mean indicates normal bone density.
- A T-score of 1 to 2.5 SD below the young adult mean (-1 to -2.5 SD) indicates low
- A T-score of 2.5 SD or more below the young adult mean (more than -2.5 SD) indicates
the presence of osteoporosis.
In general, the risk for bone fracture doubles with every SD below normal. Thus, a
person with a BMD of 1 SD below normal (T-score of -1) has twice the risk for bone
fracture as a person with a normal BMD. When this information is known, people with
a high risk for bone fracture can be treated with the goal of preventing future fractures.
Severe (established) osteoporosis is defined as having a bone density that is more
than 2.5 SD below the young adult mean with one or more past fractures due to osteoporosis.
Secondly, your BMD is compared to an age-matched norm. This is called your Z-score.
Z-scores are calculated in the same way, but the comparisons are made to someone of
your age, sex, race, height, and weight.
In addition to bone densitometry testing, your healthcare provider may recommend other
types of tests, such as blood tests, which may be used to find the presence of kidney
disease, evaluate the function of the parathyroid gland, evaluate the effects of cortisone
therapy, and/or assess the levels of minerals in the body related to bone strength,
such as calcium.
Why might I need a bone density test?
A bone density test is mainly done to look for osteoporosis (thin, weak bones) and
osteopenia (decreased bone mass) so that these problems can be treated as soon as
possible. Early treatment helps to prevent bone fractures. The complications of broken
bones related to osteoporosis are often severe, particularly in the elderly. The earlier
osteoporosis can be diagnosed, the sooner treatment can be started to improve the
condition and/or keep it from getting worse.
A bone density testing may be used to:
- Confirm a diagnosis of osteoporosis if you have already had a bone fracture
- Predict your chances of fracturing a bone in the future
- Determine your rate of bone loss
- See if treatment is working
There are many risk factors for osteoporosis and indications for densitometry testing.
Some common risk factors for osteoporosis include:
- Post-menopausal women not taking estrogen
- Advancing age, women over 65 and men over 70
- Family history of hip fracture
- Using steroids long-term or certain other medicines
- Certain diseases, including rheumatoid arthritis, type 1 diabetes mellitus, liver
disease, kidney disease, hyperthyroidism, or hyperparathyroidism
- Excessive alcohol consumption
- Low BMI (body mass index)
What are the risks of a bone density test?
Bone densitometry testing uses a low dose of radiation. You may want to ask your healthcare
provider about the amount of radiation used during the procedure and the risks related
to your particular situation. It is a good idea to keep a record of your radiation
exposure, such as previous CT scans and other types of X-rays, so that you can tell
your healthcare provider. Risks associated with radiation exposure may be related
to the cumulative number of X-ray exams and/or treatments over a long period.
If you are pregnant or think that you may be, you should tell your healthcare provider.
Radiation exposure during pregnancy can lead to birth defects.
There may be other risks depending on your specific medical condition. Be sure to
discuss any concerns with your healthcare provider before the procedure.
Certain factors or conditions may interfere with a bone density test. These include
- Metal jewelry or other metal objects
- Body piercing
- A barium X-ray within 10 to 14 days of testing
- Calcified arthritic sclerosis of the posterior vertebrae
- Calcified abdominal aortic aneurysm
- Healed bone fractures
- Metallic clips from previous stomach surgery
How do I get ready for a bone density test?
- Your healthcare provider will explain the procedure to you and ask if you have any
- You will be asked to sign a consent form that gives your permission to do the test.
Read the form carefully and ask questions if anything is not clear.
- Generally, no prior preparation, such as not eating or not taking medicine, is needed.
You may be told to stop taking calcium supplements 24 to 48 hours before your bone
- Tell the technologist if you are pregnant or think you may be.
- Based on your medical condition, your healthcare provider may give you other instructions
on what to do before bone density testing.
What happens during a bone density test?
This test may be done on an outpatient basis or as part of your stay in a hospital.
Procedures may vary depending on your condition and your healthcare provider's practices.
Generally, it follows this process:
- In some cases, you may stay dressed but will be asked to remove all metallic objects,
such as belt buckles, zippers, coins, keys, jewelry, dental appliances, and eye glasses.
In other cases, you will be given a gown to wear so that no buttons, zippers, or hooks
will interfere with the imaging process.
- You will be positioned on an X-ray table, lying flat on your back. Your legs will
be supported on a padded box which helps to flatten the pelvis and lumbar spine.
- Under the table, a photon generator will pass slowly beneath you, while an X-ray detecting
camera passes above the table parallel to the photon generator beneath. Together,
they project pictures of the lumbar spine (lower back) and hip bones onto a computer
screen. You will be asked to stay very still and may be asked to hold your breath
for a short time in order to get a very clear picture.
- The radius, a bone in your forearm, or your heel may be scanned depending on your
healthcare provider's request. The computer will calculate the amount of photons that
are not absorbed by the bones to determine the bone mineral content. The bone mineral
density will then be calculated by the healthcare provider.
The entire scan takes about 30 minutes. A portable scan that checks only your forearm,
finger, hand, or foot, takes a bone density reading in a few minutes.
While the bone densitometry procedure itself causes no pain, the movements of the
body parts being examined may cause some discomfort or pain, particularly if you have
recently had surgery or an injury. The technologist will use all possible comfort
measures and complete the procedure as quickly as possible to reduce any discomfort
What happens after a bone density test?
There is no special type of care after a bone density test. You may go back your usual
diet and activities, unless your healthcare provider advises you differently.
Before you agree to the test or the procedure make sure you know:
- The name of the test or procedure
- The reason you are having the test or procedure
- What results to expect and what they mean
- The risks and benefits of the test or procedure
- What the possible side effects or complications are
- When and where you are to have the test or procedure
- Who will do the test or procedure and what that person’s qualifications are
- What would happen if you did not have the test or procedure
- Any alternative tests or procedures to think about
- When and how will you get the results
- Who to call after the test or procedure if you have questions or problems
- How much will you have to pay for the test or procedure