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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.

Next Article:

Osteoporosis Glossary

  • Bone Mineral Density - A measurement of the amount of calcium and minerals in bone tissue.
  • Calcium - A mineral in (and vital to) your bones. If your body lacks calcium, it takes it from bones.
  • DEXA (dual energy X-ray absorptiometry) - a test used to measure bone mineral density.
  • Osteoporosis - A decrease in bone density, which increase the risk of fractures.
  • Vitamin D - A vitamin that helps your body absorb calcium.
  • View All Terms

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