title: Dual-energy X-ray absorptiometry diagnostic discordance between Z-scores and T-scores in a young Iranian population.
abstract: 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: 1. MD, MPH, General Physician, Research Fellow, Endocrinology and Metabolism Research Center, Vali-Asr Hospital, Tehran University of Medical Sciences, Tehran, Iran. bh.medstudent@gmail.com.
authors.forename: Behnam
authors.initials: B
authors.lastname: Heidari
authors.affiliation: 2. MD, PhD by Research Student, Endocrinology & Metabolism Research Center, Endocrinology and Metabolism Clinical Sciences Institute, Tehran University of Medical Sciences, Tehran, Iran. patricia.kh@gmail.com.
authors.forename: Patricia
authors.initials: P
authors.lastname: Khashayar
authors.affiliation: 3. MD, PhD, Epidemiologist, Assistant Professor, Rasul-Akram Hospital, Iran University of Medical Sciences Tehran, Iran. mohsen_rez@yahoo.com.
authors.forename: Mohsen
authors.initials: M
authors.lastname: Rezai Homami
authors.affiliation: 4. MD, General Physician, Research Fellow, Endocrinology & Metabolism Research Center, Endocrinology and Metabolism Clinical Sciences Institute, Tehran University of Medical Sciences, Tehran, Iran. ap.medstudent@gmail.com.
authors.forename: Atieh
authors.initials: A
authors.lastname: Pajouhi
authors.affiliation: 5. MD, Associate Professor, Endocrinology & Metabolism Research Center, Endocrinology and Metabolism Clinical Sciences Institute, Tehran University of Medical Sciences, Tehran, Iran. soltania@tums.ac.ir.
authors.forename: Akbar
authors.initials: A
authors.lastname: Soltani
authors.affiliation: 6. MD, Professor,Endocrinology & Metabolism Research Center, Endocrinology and Metabolism Clinical Sciences Institute, Tehran University of Medical Sciences, Tehran, Iran. larijani@tums.ac.ir.
authors.forename: Bagher
authors.initials: B
authors.lastname: Larijani
keywords: Bone Mineral Density; Iran; Osteoporosis; T-scores; Z-scores