The following table contains the World Health
Organization's definitions of osteoporosis based on
bone density T-scores.
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 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.
Low bone density values may be caused by other problems,
Your bone density value may also be compared to
other people of your age, sex, and race. This is called your Z-score. It is
given in standard deviations (SD) from the average value for your age
- A negative (–) value means that your bones
are thinner (lower bone density) and weaker than most people in your age group.
The more negative the number is, the less bone density you have compared with
others in your age group.
- A positive (+) value means that your
bones are thicker and stronger than most people in your age group.
What Affects the Test
Reasons you may not be able to
have the bone density test or why the results may not be helpful include:
- Inability to be correctly positioned during the
- Having a broken bone in the past. This can cause
falsely high bone density results.
- Arthritis of your spine. In this case, the changes
caused by arthritis in the spine may not make the spine the best place to
measure for osteoporosis.
- Metal implants from hip
replacement surgery or hip fracture.
- Having an X-ray test
barium within 10 days of the bone density test.