DEXA (dual energy x-ray absorptiometry) scans are used to measure bone mineral density (BMD). Using x-rays of different energies permits differentiation between bone and other soft tissue absorption. Measurements are generally performed on the:
lower spine
femur (total and femoral neck)
forearm
T and Z scores
DEXA is used to derive two scores: T and Z
T-score is the number of standars deviations away from a sex-matched adult aged 30 years
Z-score is the number of standard deviations away from the sex and age matched mean
Z-scores are generally used to assess bone mineral density in people under 50 years of age
Diagnosis of osteoporosis is based on the World Health Organisation T-score criteria (Table 1)