There are uncertainties concerning the optimal threshold value of bone mineral density (BMD) for the diagnosis of osteoporosis using dual-energy X-ray absorptiometry (DXA). The most widely accepted clinical criteria are based on T- and Z-scores, derived statistically from an age-dependent BMD reference range that includes healthy young adults. This study has compared different analyses of BMD data of healthy, nonfractured, adult white females aged 18-90 years, consisting of 953 studied with DXA in the L1-L4 spine and 1018 measured at the hip. Four regression curves were applied to each reference data set; mean, peak BMD (PBMDR) and the age-independent standard deviation (SDR) were calculated. These data, plus derived T-score thresholds, were compared with equivalent values (PBMDYN, SDYN) determined from BMDs of a subgroup of young normals. Choice of regression curve caused a variation of 0.044 g/cm(2) in spinal PBMDR and 0.015-0.022 g/cm(2) in the hip. The variation in calculated SDR between the regressions was minimal (maximum variation, 0.03 SD unit in the spine). A split-linear model was chosen as the best overall fit for both the spine and the hip on the basis of goodness-of-fit and biological plausibility. PBMDR and PBMDYN varied by less than 1% at the spine or hip. Although the difference between SDR and SDYN was less than or equal to7% for the hip sites, SDR was 0.022 g/cm(2) > SDYN for the spine (17% difference). At each hip site, BMD T-score thresholds, derived from regression analysis of the entire reference range (T-R) or from young normals only (T-YN), were not significantly different; however, equivalent spinal values differed by 0.062 g/cm 2 for T = -2.5. The percentage of the Australian female population (AFP) aged 50 yr or older and classified as osteoporotic, using population census data and the split-line-based T-score threshold of T-R = -2.5, was 23% for spinal BMD and 17% for the total hip. For T-YN = -2.5, the values were 36% (spine) and 17% (total hip). The hip BMDs of this study were greater than those of NHANES III in the third, seventh and eighth decades by as much as 0.6 SD. This produced a difference of 0.049-0.077 g/cm(2) for T-YN = -2.5 between the two reference ranges. However, this study is in broad agreement with an Eastern Australian and the U.S. DXA manufacturer's reference range.
Price, R. I., Walters, M. J., Rettalack, R. W., Henderson, N. K., Kerr, D., Henzell, S., Dhaliwal, S., & Prince, R. (2003). Impact of the Analysis of a Bone Density Reference Range on Determination of the T-Score. Journal of Clinical Densitometry, 6(1), 51-62. https://doi.org/10.1385/JCD:6:1:51