||Bone mineral density (BMD) measurements are
frequently performed repeatedly for each patient. Subsequent
BMD measurements allow reproducibility to be
assessed. Previous studies have suggested that reproducibility
may be influenced by age and clinical status.
The purpose of the study was 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 three distinct groups of
subjects: healthy young volunteers, postmenopausal
women and patients with chronic rheumatic diseases.
Two hundred twenty-two subjects underwent two subsequent
BMD measurements of the spine and hip. There
were 60 young healthy subjects, 102 postmenopausal
women and 60 patients with chronic rheumatic diseases
(33 rheumatoid arthritis, 10 ankylosing spondylitis and
10 other systemic diseases). Forty-five patients (75%)
among the third group were receiving corticosteroids.
Reproducibility was expressed as the smallest detectable
difference (SDD), coefficient of variation (CV), least
significant change (LSC) and intraclass correlation
coefficient (ICC). Sources of variation were investigated
by linear regression analysis. The median interval between
measurements was 0 days (range 0–7). The mean
difference (SD) between the measurements (g/cm2) was
)0.0001 (±0.003) and )0.0004 (±0.002) at L1-L4 and
the total hip, respectively. At L1-L4 and the total hip,
SDD (g/cm2) was ±0.04 and ±0.02, CV (%) was 2.02
and 1.29, and LSC (%) 5.60 and 3.56, respectively. The
ICC at the spine and hip was 0.99 and 0.99, respectively.
Only a minimal difference existed between the groups.
Reproducibility in the three groups studied was good. In
a repeated DXA scan, a BMD change, 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 ±0.04 g/cm2 at L1-L4 and
±0.02 g/cm2 at the total hip should be considered significant.
This reproducibility seems independent from
age and clinical status and improved in the hips by
measuring the dual femur.