Reproducibility of bone mineral density measurement in daily practice
- M C Lodder1,
- W F Lems1,
- H J Ader2,
- A E Marthinsen1,
- S C C M van Coeverden3,
- P Lips4,
- J C Netelenbos4,
- B A C Dijkmans1,
- J C Roos5
- 1Department of Rheumatology, VU University Medical Centre, Amsterdam, The Netherlands
- 2Department of Clinical Epidemiology and Biostatistics, VU University Medical Centre, Amsterdam, The Netherlands
- 3Department of Paediatrics, VU University Medical Centre, Amsterdam, The Netherlands
- 4Department of Endocrinology, VU University Medical Centre, Amsterdam, The Netherlands
- 5Department of Nuclear Medicine, VU University Medical Centre, Amsterdam, The Netherlands
- Correspondence to:
Dr M C Lodder
Department of Rheumatology, VU University Medical Centre, Room 4A42, PO Box 7057, 1007 MB Amsterdam, The Netherlands;
- Accepted 28 April 2003
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.
- BMD, bone mineral density
- BMI, body mass index
- CV, coefficient of variation
- DXA, dual energy x ray absorptiometry
- ICC, intraclass correlation coefficient
- LSC, least significant change
- SDD, smallest detectable difference