Your Bone Density Scan

Your Bone Density

Your bone density will be compared with the bone density expected for a young healthy adult (your T-score) and also with a healthy adult of your own age, gender and ethnicity (your Z-score).

The difference is calculated as a standard deviation (SD) score. This measures the difference between your bone density and the expected value in terms of the natural spread of values in the healthy population.

T scores defined by The WorldHealth Organization:

  • Higher than 1 SD is normal
  • Between -1 and -2.5 SD is defined as mildly reduced bone mineral density
  • Below -2.5 SD is defined as osteoporosis

Z score

  • Below -2 indicates your bone density is lower than it should be for someone of your age.
  • You can enter this score into the Fracture Risk Assessment Tool (FRAX)

The FRAX tool

  • The World Health Organization has developed a 10 year Fracture Risk Assessment Tool to help predict a person's risk of fracture in an age range between 40-90 years.
  • The tool is based on bone mineral density (BMD) and other relevant risk factors such as age and sex.
  • The algorithms that are used give a 10-year probability of hip fracture and a 10-year probability of major fracture in the spine, hip, shoulder or forearm.