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Logo of annrheumdAnnals of the Rheumatic DiseasesCurrent TOCInstructions for authors
 
Ann Rheum Dis. Mar 2004; 63(3): 285–289.
PMCID: PMC1754906
Reproducibility of bone mineral density measurement in daily practice
M Lodder, W Lems, H Ader, A Marthinsen, S C C M van Coeverden, P Lips, J Netelenbos, B Dijkmans, and J Roos
Department of Rheumatology, VU University Medical Centre, Amsterdam, The Netherlands. secr.reumatologie/at/vumc.nl
Background: Bone mineral density (BMD) measurements are frequently performed repeatedly for each patient. Subsequent BMD measurements allow reproducibility to be assessed.
Objective: To examine the reproducibility of BMD by dual energy x ray absorptiometry (DXA) and to investigate the practical value of different measures of reproducibility in a group of postmenopausal women.
Methods: Ninety five women, mean age 59.9 years, underwent two subsequent BMD measurements of spine and hip. Reproducibility was expressed as smallest detectable difference (SDD), coefficient of variation (CV), and intraclass correlation coefficient (ICC). Sources of variation were investigated by multilevel analysis.
Results: The median interval between measurements was 0 days (range 0–45). The mean difference (SD) between the measurements (g/cm2) was -0.001 (0.02) and -0.0004 (0.02) at L1-4 and the total hip, respectively. At L1-4 and the total hip, SDD (g/cm2) was ±0.05 and ±0.04 and CV (%) was 1.92 and 1.59, respectively. The ICC at spine and hip was 0.99.
Conclusions: Reproducibility in the postmenopausal women studied was good. In a repeated DXA scan a BMD change exceeding 2√2CV (%), the least significant change (LSC), or the SDD should be regarded as significant. Use of the SDD is preferable to use of the CV and LSC (%) because of its independence from BMD and its expression in absolute units. Expressed as SDD, a BMD change of at least ±0.05 g/cm2 at L1-4 and ±0.04 g/cm2 at the total hip should be considered significant.
Figure 1
Figure 1
Graph of the difference score against the mean score of the two total hip BMD measurements (g/cm2) in postmenopausal women (open diamonds) and children (closed squares). The outermost (solid) lines represent the 95% limits of agreement for postmenopausal (more ...)
Figure 2
Figure 2
Graph of the difference score against the mean score of the two lumbar spine BMD measurements (g/cm2) in postmenopausal women (open diamonds) and children (closed squares). The outermost (solid) lines represent the 95% limits of agreement for postmenopausal (more ...)
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