The best diagnostic test to assess bone density is a bone mineral density (BMD) test. The most widely recognized bone mineral density test is a DEXA scan. A DEXA scan stands for Dual-Energy X-ray Absorptiometry. This low level x-ray measures the density of three important bone sites and is a completely painless, non-invasive test that takes minutes to complete. At the Virginia Spine Institute, we have an in-house DEXA suite and coordinate imaging when necessary with other appointments. A DEXA scan may be used to evaluate for osteopenia or osteoporosis and as part of surgical planning.
In a DEXA scan, the amount of mineralized tissue within a section of spine or hip is measured. The value is compared to others of the same age and gender, measured as a Z score, and to healthy 30-year olds of the same gender at peak bone mass, measured as a T score. These scores are expressed as a deviation from the average. This indicates how far above or below normal one’s bone quality lies. A decrease in BMD clearly presents great risk of fracture. For each 1-point T-score decrease, the risk of fracture doubles.
The World Health Organization criterion defines osteopenia and osteoporosis as:
- Normal bone density is within one standard deviation of peak bone mass, T score 0 to -1.0
- Osteopenia is when the bone mass is between 1 and 2.5 standard deviations below peak bone mass, T score -1.1 to -2.5
- Osteoporosis is when the bone mass is 2.5 standard deviations below peak bone mass, T score less than -2.5
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