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Estimation of lumbar spine bone mineral density by dual-energy X-ray absorptiometry: standard anteroposterior scans vs sub-regional analyses of whole-body scans

Endocrinology Clinic, Alexandrovska Hospital, Medical University of Sofia, BG 1431 Sofia, Bulgaria

Correspondence: Dr M Boyanov, Endocrinology Clinic, Alexandrovska Hospital, 1 G Sofiiski str, Sofia 1431, Bulgaria. E-mail: boyanov{at}alexandrovska-hospital.bg

Dual-energy X-ray absorptiometry of the lumbar spine (anteroposterior (AP) L₁–L₄ DXA) is one of the standards for testing bone density (BMD). Whole-body (WB) DXA scanning allows analysis of the L-spine (WB–LS). The objective of this study was (i) to predict the AP L₁–L₄ BMD from the WB–LS BMD, and (ii) to compare WB and AP L₁–L₄ T-scores. 132 women participated in the study (age, 50.84±9.69 years; range, 21–74 years). AP L₁–L₄ BMD was measured on a Hologic QDR 4500-A densitometer, and was followed by a WB scan. Linear regression analyses and curve estimations were performed for area, bone mineral content (BMC), BMD and T-scores. Precision errors for BMD from AP scans and WB–LS scans were 1.37% and 1.65%, respectively. The best linear correlations were found for BMD, followed by the T-scores (R = 0.882 and 0.871; p<0.001). A power model for BMC (R² = 0.630) and a model S for BMD and the scanned area (R² = 0.841 and 0.539) were built. Discordant classification between AP L₁–L₄ and WB T-scores was found in 12.73% and 19.09% cases, respectively. WB T-score cut-off values of –2.35 and –0.90 produced the best sensitivity-to-specificity ratio in the diagnosis of lumbar spine osteoporosis and low bone mass. In conclusion, WB–LS analysis may provide data for the indirect estimation of spinal BMD.