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Bone mineral density (BMD) measurement using dual-energy X-ray densitometry (DXA) has long been established as the gold standard in the screening of osteoporosis. BMD measurement provides two indices: the [i]Z[/i]-score and the [i]T[/i]-score. The [i]Z[/i]-score is the number of standard deviations that the individual measurement differs from the mean value of the healthy population, matched for race, age and sex. Accordingly, the [i]T[/i]-score is the number of standard deviations that the individual measurement differs from the mean peak bone density of the healthy young population, matched for race and sex. The manufacturers, when setting normative data, take into account three races, meaning the Caucasian, Black and Asian populations. It is becoming apparent, however, that, within the same race, there are significant differences across different countries. This important issue is highlighted in the article by Noon and colleagues in the latest issue of [i]Osteoporosis International[/i] [1]. The authors have assessed the [i]Z[/i]-scores of women participating in three different clinical studies conducted in the UK, using the manufacturer’s US normative data. In all three studies, the mean [i]Z[/i]-scores were above 0, meaning that the normal BMD of the UK women is higher than that of the US women.


  • George Creatsas
    2nd Department of Obstetrics and Gynecology, Aretaieion Hospital, Athens, Greece


  1. Noon E, Singh S, Cuzick J, et al. Significant differences in UK and US female bone density reference ranges. Osteoporosis Int 2010; January 9. E-pub ahead of print.
  2. Lunt M, Felsenberg D, Adams J, et al. Population-based geographic variations in DXA bone density in Europe: the EVOS Study. European Vertebral Osteoporosis. Osteoporosis Int 1997;7:175-89.
  3. Kaptoge S, da Silva JA, Brixen K, et al. Geographical variation in DXA bone mineral density in young European men and women. Results from the Network in Europe on Male Osteoporosis (NEMO) study. Bone 2008;43:332-9.
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