Bone Scans and Bone Health Screenings
When should you get a bone density scan, and why?
Interpreting Your DEXA Bone Scan Results: T-Scores and Z-Scores
DEXA scores are reported as "T-scores" and "Z-scores."
- The T-score is a comparison of a person's bone density with that of a healthy 30-year-old of the same sex.
- The Z-score is a comparison of a person's bone density with that of an average person of the same age and sex.
Lower scores (more negative) mean lower bone density:
- A T-score of -2.5 or lower qualifies as osteoporosis.
- A T-score of -1.0 to -2.5 signifies osteopenia, meaning below-normal bone density without full osteoporosis.
Multiplying the T-score by 10% gives a rough estimate of how much bone density has been lost.
Z-scores are not used to formally diagnose osteoporosis. Low Z-scores can sometimes be a clue to look for a cause of osteoporosis.
DEXA Bone Scans: What Your T-Score Means
Being told your bones are thin is cause for concern, but not alarm. If your T-score is low, what can you expect?
First of all, unless you're a woman past menopause or a man older than 50, your risk of fracture is very low. In these groups, even with a T-score less than -2.5, bones are usually strong and treatment isn't recommended.
On the other hand, if you've been told you have osteoporosis, take it seriously. Feeling fine is no protection at all: fractures of the spine can be silent and painless. "Anyone with osteoporosis should be on some kind of treatment," according to Baker.
For those with osteopenia (T-score between -1.0 and -2.5), the picture gets confusing. It's harder to predict fracture risk in this group of people. Focusing too closely on the T-score can be a mistake. "The DEXA T-score is not a perfect predictor for bone health or fracture risk," says Rhee.
Actually, bone density (measured by T-score) is only one aspect of fracture risk. Your risk factors (see above) can be just as important. Using both the T-score and risk factors for fracture leads to better predictions.
The World Health Organization is developing a formula using risk factors in combination with the T-score to determine 10-year fracture risk. "We'll probably see this coming into use in the next few years," says Rhee.