Background: Dual-energy X-ray Absorptiometry (DXA) is considered the gold standard for non-invasive
measurement of bone mass. T-scores and Z-scores are used to present the results of bone mass. The present
study was designed to evaluate the discordance between T-scores and Z-scores calculated at a same level and its
relation with age, gender and body mass index (BMI) in a representative sample of normal population.
Methods: This cross-sectional study was conducted as a part of a comprehensive survey, Iranian Multicenter
Osteoporosis Study (IMOS), designed to assess bone health among healthy adults. Each individual underwent
both L1–L4 antero-posterior lumbar spine and hip DXA scan. The difference between the T- and Z-scores
measured at each of the four skeletal sites was then calculated.
Results: A -1.21 to 1.21 point difference was noted in the Z- and T- scores measured at each site. While the
difference between the T- and Z-scores was less than 0.5 SD in most of the cases, the difference was higher than
1 SD in about 5% of the subjects.
Conclusion: Standardization of Z-score definition and calculation techniques as well as developing an ethnicity-matched
reference population is needed to improve the reliability of DXA-generated Z-scores
