2.2.1 Quantifying osteoporosis
When bone mineral density (on a DXA scan) is more than 2.5 standard deviations below the mean peak bone mass for a young woman, the individual is said to have osteoporosis.
The T-score is the name for the number of standard deviations a person’s BMD is from the young adult mean. So a T-score of -2.5 is the cut-off for defining osteoporosis by BMD.
However, bone strength is a spectrum and many people without a diagnosis of ‘osteoporosis’ by DXA scan have reduced bone strength. Where DXA results are between 1 and 2.5 SD below the young adult mean, this is called ‘osteopenia’. Because osteopenia is more common, and is associated with reduced bone strength, most people who fracture have osteopenia rather than osteoporosis.
2.2 What is osteoporosis?