Use of Bioelectrical Impedance Analysis for the Measurement of Appendicular Skeletal Muscle Mass/Whole Fat Mass and Its Relevance in Assessing Osteoporosis among Patients with Low Back Pain: A Comparative Analysis Using Dual X-ray Absorptiometry.

Study Design: Cross-sectional observational study.
Purpose: To compare measurements of appendicular skeletal muscle mass (ASMM) and whole fat mass (WFM) obtained using dualenergy X-ray absorptiometry (DXA) and bioelectrical impedance analysis (BIA) among patients with low back pain (LBP). Moreover, the study investigated the correlation between BIA-based ASMM and DXA-based bone mineral density (BMD). Overview of the Literature: If reliable, BIA may be a useful alternative to DXA as a screening tool for sarcopenia and osteoporosis among patients with LBP.
Methods: Measurements were performed in 130 patients, including BMD of the lumbar spine and femoral neck. The correlation between DXA and BIA as well as between BIA-ASMM and BMD were evaluated.
Results: BIA and DXA were highly correlated in both male and female patients (r =0.73-0.90, p <0.0001). However, BIA consistently overestimated ASMM by 1.5-2.5 kg on an average (p <0.0001) and underestimated WFM (-4.0 to -2.7 kg) on an average (p <0.0001). BIA-based ASMM correlated with BMD of the lumbar spine in both male and female patients (r =0.28-0.37, p ≤0.02) and that of the femoral neck (r =0.34-0.51, p ≤0.005). Regarding the calculated skeletal muscle index (SMI: ASMM/height [m2]) used as a criterion for sarcopenia, BIA-based SMI correlated with BMD of the lumbar spine in male patients (r =0.44, p =0.0004) and that of the femoral neck in female patients (r =0.33, p =0.009).
Conclusions: BIA may be a favorable alternative to DXA as a screening tool for sarcopenia and osteoporosis among patients with LBP. Considering the overestimation of BIA-based ASMM and SMI, we recommend using the cutoff values for sarcopenia of 7.9 kg/m2 for males and 6.1 kg/m2 for females.