Differences in precision in bone mineral density measured by SXA and DXA: the NOREPOS study

Abstract

The aims were to compare the precision (reliability) in single X-ray (SXA) and dual X-ray (DXA) absorptiometry, and to compare smallest detectable difference (SDD). An additional aim was to examine determinants for precision in bone mineral density (BMD). BMD was measured by SXA (DTX-100, Osteometer) in the forearm and by DXA (Lunar Expert) in the forearm and in the hip. Two measurements were performed at each site/method, and 195 of 207 participants had complete datasets. Participants were aged 47-49 and 71-74 years. The precision was estimated by Root Mean Square Standard Deviation (RMS SD) with 95% Confidence Interval (95%CI) and the corresponding coefficients of variation (CV%). Determinants (age, gender, BMD) were analysed by multiple linear regression with log (SD) and log (CV) as dependent variables. RMS SD tended to be largest in older women and in those with low BMD. RMS SD for SXA and DXA forearm was 4.6 (4.2-5.1) and 6.8 (6.1-7.4) and the corresponding CVs 1.0% and 1.4%. RMS SD for DXA hip was 11.0 (9.9-12.0) with CV 1.2%. To detect a 3% change in BMD one would need two repeated measurements by DXA in the distal forearm at each of two consultations, but only one measurement by SXA in the distal forearm and also only one measurement by DXA in the hip. Precision differed by type of densitometer affecting the number of repeated measurements needed to detect a given BMD difference.

Weight loss and distal forearm fractures in postmenopausal women

“…The reasons for nonparticipation in the BMD measurements were mainly technical and unlikely to be biased. Another strength is that forearm SXA measurements have shown high precision [30]. Further, in contrast to self-reported body weight, our standardized measurements of body weight are likely to provide more accurate estimates of weight change.…”

An example of a successful national research network in epidemiology – The Norwegian Epidemiologic Osteoporosis Studies (NOREPOS)

“…Methodological studies comparing the performance of densitometers used in Tromsø, Hordaland, Nord-Trøndelag and Oslo were carried out (35)(36)(37)(38). In one of these, a total of 16 participants agreed to travel between study sites and had measurements on each of the DXA machines in Tromsø, Bergen and Oslo.…”

Cohort profile: Norwegian Epidemiologic Osteoporosis Studies (NOREPOS)

“…For assessment of regional differences in BMD, the measurement levels of the densitometers had to be comparable. Hence, validation, precision and calibration studies, as well as inter-study comparisons, have been conducted [29][30][31][32]. We designed and carried out a methodological study comparing the performance of densitometers used in Tromsø, Bergen and Oslo.…”

“…We have also examined differences in precision of BMD measured by SXA and DXA [32]. SXA showed better precision than DXA in the forearm, and in order to detect a 3% change in BMD one would need two repeated measurements by DXA in the distal forearm at each of two consultations, but only one measurement by SXA at the same site.…”

“…All BMD measurements followed a similar protocol and have been analyzed with regard to validation, precision and artefacts, as well as inter-study comparisons [14,32,58,59]. Regarding use of data from CONOR and the BMD measurements, potential weaknesses include different age groups at the various study sites.…”