Osteoporosis defined as a T-score -2.5 SD or lower.

• A. -1 SD or higher
• B. -2.0 SD or higher
• C. -3.0 SD or higher
• D. -2.5 SD or lower

Answer: (D)

Bone mineral density is summarized with a T-score, which measures how far a person’s density deviates from the young healthy adult mean in standard deviation units. Osteoporosis is defined as a T-score of -2.5 or lower because fracture risk rises substantially when bone density falls 2.5 standard deviations below that young reference. Values above this threshold do not meet the osteoporosis criteria; densities from about -1.0 to -2.5 are labeled osteopenia, indicating lower density and higher fracture risk but not the osteoporosis cut-off. A T-score of -3.0, for example, would still be categorized as osteoporosis by the same criterion (-2.5 or lower), since it lies beneath the threshold.