A bone mineral density (BMD) test measures your bone density and compares it to the young adult mean, or the average bone density of a healthy young adult. Using the BMD test, your physician gets a result called a T score. Your physician uses your T score to determine your risk for osteoporosis.

• Normal bone density is a T score within 1 standard deviation (SD) of the young adult mean.
• Low bone mass is a T score 1 to 2.5 SD below the young adult mean.
• Osteoporosis is a T score that is 2.5 SD or more below the young adult mean.
• Severe osteoporosis is a T score more than 2.5 SD below the young adult mean in a person who has already had a bone fracture.