dual-energy x-ray absorptiometry diagnostic discordance between z-scores and t-scores in a young iranian population

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.