How to Understand Your Results
At first, you may find it difficult to understand your bone
mineral density (BMD) test results. The following information
should help you understand what your test results mean. Of course, it
is always necessary to discuss the meaning of your results with your
doctor or medical professional.
Your first BMD
test tells you the current density of your bones at that specific
time. However, it can not tell you if you have lost bone or are
currently losing bone. The only way to diagnose bone loss is to have a
repeat BMD test, usually two years later. Your doctor or medical
professional can determine whether you are losing bone by comparing the
initial and repeat BMD test results.
There are two scores used by experts to interpret bone density test results, the T-score and the Z-score.
What is a T-score and what does it mean?
The
World Health Organization (WHO) uses T-scores to define normal bone
mass, low bone mass (or osteopenia), and osteoporosis. The T-score
compares your bone density to the average bone density of young healthy
adults of your same gender . By using the diagram below, you can see
how T-scores are used to define the status of your bone health.
What is a Z-score and what does it mean?
A
Z-score compares your bone density to the average values for a person
of your same age and gender. A low Z-score (below –2.0) is a warning
sign that you have less bone mass (and/or may be losing bone more
rapidly) than expected for someone your age. If your Z-score is low,
your medical professional may recommend additional tests to better
understand why your bone mass is so low or she/he may refer you to an
osteoporosis specialist.
What is low bone mass and how is it diagnosed?
Low
bone mass, often called osteopenia, is not a disease but a condition in
which your bone density, or bone thickness, is lower than the average
bone density of young healthy adults of your same gender. Low bone mass
is diagnosed when your T-score is between –1 and –2.5. If you have been
diagnosed with low bone mass, it is important to speak to your doctor
or medical professional about your results and take action to promote
healthy bones.
What is osteoporosis and how is It diagnosed?
Osteoporosis
is a disease that causes bones to become thin and weak, often resulting
in fractures (broken bones) A BMD test can diagnose
osteoporosis when your T-score is –2.5 or below. The lower your bone
mass, the greater your risk for fracture. Osteoporosis can also be
diagnosed if you have a history of fractures without trauma.
What if I have low bone mass or osteoporosis?
If
your BMD test results indicate that you have osteoporosis, your
doctor or medical professional may prescribe a medication for
osteoporosis treatment. If you have low bone mass along with strong
risk factors for osteoporosis and/or fracture, your doctor may decide
to prescribe a medication for osteoporosis prevention. After a
medication is prescribed for you, repeat BMD tests may be used to
monitor how your bones have responded to the treatment.
It
is ideal to have follow-up BMD tests performed on the same machine, at
the same location, as your first bone density test. However, if you are
not able to return to the same location, select a center that has the
same model of DXA machine. This is necessary in order to make accurate
comparisons and to be able to monitor the effectiveness of treatments
for osteoporosis.
Will a BMD test alone tell me my risk for breaking a bone?
The
BMD test measures bone quantity (the amount of bone you have). It will
tell you if you have a low amount of bone (or low bone mass). Low bone
density is one of the best predictors of fracture risk; if your
bone mass is low, you may be at greater risk for breaking a
bone.
However, in addition to your bone density test
results, your doctor or medical professional will also consider several
other factors in order to define your risk for fracture. For example,
the risk of fracture increases with age. Bone quality is a factor that
cannot be measured by a BMD test. In fact bone quality can
not be easily measured with our current technology. Experts believe
that bone quality plays an important role in determining bone
strength. Perhaps differences in bone quality can help explain
why there are some risk factors for fracture that are independent of
one's BMD test results.
The following risk factors for hip fracture are independent of your BMD test results:
- a personal history of fracture (you are more likely to break a bone if you have already broken one)
- family history of maternal hip fracture (if your mother broke her hip, you are at greater risk for a hip fracture)
- low body weight (women weighing less than 127 pounds)
- frailty
- a tendency to fall frequently
- current cigarette smoking.
In
some cases, your doctor or medical professional may recommend
additional tests to better understand your fracture risk. Research is
helping us to better understand other risk factors for fracture that
cannot easily be measured such as bone quality.
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