Bone Mineral Density
How It Feels
A bone mineral density test does not cause
pain. If you have back pain, it may be uncomfortable to lie still on a table
during the scan.
During a bone mineral density (BMD) scan, you are
exposed to a very low dose of radiation. A BMD scan is not recommended for
pregnant women because of the radiation exposure to the unborn baby.
A bone mineral density (BMD) test measures
the density of minerals (such as
calcium) in your bones using a special
computed tomography (CT) scan. Results are usually available in 2 to 3
Results of bone mineral density tests can be reported in
Your T-score is your BMD compared to the
average score of a healthy 30-year-old. It is expressed as a standard deviation
(SD), which is a statistical measure of how closely each person in a group is
to the average (mean) of the group. The average BMD is determined by measuring
the bone density of a large group of healthy 30-year-olds (young adult
reference range). BMD values are then reported as a standard deviation from the
mean of this reference group. Almost all 30-year-old people have a BMD value
within 2 standard deviations of this mean.
- A negative (-) value indicates that you have
thinner bones (lower bone density) than an average 30-year-old. The more
negative the number is, the less bone density you have compared with an average
- A positive (+) value indicates that your bones are
thicker and stronger than an average 30-year-old.
The following table contains the World Health
Organization's definitions of osteoporosis based on
bone mineral density T-scores.
Bone mineral density
Less than 1 standard deviation (SD) below the young
adult reference range (more than -1)
| Low bone mass (osteopenia): |
1 to 2.5 SDs below the young adult reference range (-1
More than 2.5 SDs below the young adult reference range
(-2.5 or less)
If your bone mineral density test
result is low:
- You may have
osteoporosis. Doctors usually use the lowest T-score
to diagnose osteoporosis. For example, if your T-score at your spine is -3 and
your T-score at your hip is -2, the spine T-score would be used to diagnosis
- You have a higher-than-average chance of breaking a
bone. The more negative your T-score, the greater your chances of breaking a
bone during a fall or from a minor injury. Every change of 1 SD means a twofold
increase in the risk of fracture at that site. For example, if you have a
T-score of -1, your chances of having a broken bone are 2 times greater than if
your T-score was 0.