title: Impact of the analysis of a bone density reference range on determination of the T-score.
abstract: 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 (PBMD(R)) and the age-independent standard deviation (SD(R)) were calculated. These data, plus derived T-score thresholds, were compared with equivalent values (PBMD(YN), SD(YN)) determined from BMDs of a subgroup of young normals. Choice of regression curve caused a variation of 0.044 g/cm(2) in spinal PBMD(R) and 0.015-0.022 g/cm(2) in the hip. The variation in calculated SD(R) 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. PBMD(R) and PBMD(YN) varied by less than 1% at the spine or hip. Although the difference between SD(R) and SD(YN) was < or =7% for the hip sites, SD(R) was 0.022 g/cm(2) > SD(YN) 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.
authors.affiliation: Department of Medical Technology & Physics, Sir Charles Gairdner Hospital, Perth, Western Australia. price@cyllene.uwa.edu.au
authors.forename: Roger I
authors.initials: RI
authors.lastname: Price
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Walters
authors.forename: Robert W
authors.initials: RW
authors.lastname: Retallack
authors.forename: N Kathryn
authors.initials: NK
authors.lastname: Henderson
authors.forename: Deborah
authors.initials: D
authors.lastname: Kerr
authors.forename: Sarah
authors.initials: S
authors.lastname: Henzell
authors.forename: Satvinder
authors.initials: S
authors.lastname: Dhaliwal
authors.forename: Richard L
authors.initials: RL
authors.lastname: Prince
mesh_terms: D015502:Absorptiometry, Photon; D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001315:Australia; D015519:Bone Density; D005260:Female; D006615:Hip; D006801:Humans; D008875:Middle Aged; D015233:Models, Statistical; D010024:Osteoporosis / Q000175:diagnosis; D012016:Reference Values; D012044:Regression Analysis; D013131:Spine / Q000737:chemistry