T-score: The number of standard deviations (SD) the patient is below or above the mean value for young (30 years) normal subjects (peak bone mass). The T-score is a good predictor of the fracture risk
Z-score: The number of SD the patient is below or above the mean value for age-matched normal subjects. The Z-score indicates whether or not the BMD is appropriate for age. A low Z-score is predictive of an underlying secondary cause other than age or menopause.
Absolute BMD: The actual BMD expressed in g/cm 2 . This is the value that should be used to calculate changes in BMD during longitudinal follow-up.