Category: Bone Densitometry or Body Composition

1 - Appendicular Intracellular Water Index Measured by Bioelectric Impedance Spectroscopy (BIS) as a Potential Surrogate for DXA-measured Appendicular Lean Mass

Introduction: Proposed consensus definitions of sarcopenia include lean mass measurement; thus generally requiring a whole body DXA. As this is not available everywhere and is not portable, there are situations where sarcopenia assessment is impractical. Consequently, we evaluated the potential of a mobile tool, bioelectric impedance spectroscopy (BIS), to assess muscle mass for sarcopenia determination. We hypothesized that BIS-measured appendicular intracellular water index (as a surrogate for muscle mass) corrected by height (aICW/ht2) would correlate well with ALM/ht2 and potentially allow establishment of a sarcopenia cut-point for aICW/ht2.

This study included 76 community-dwelling older individuals (61 women, 15 men) who had lean mass measured by BIS and DXA. Grip strength, gait speed, and jumping mechanography were also performed. The European working group sarcopenia definition was utilized. BIS aICW was calculated using limb length and intracellular water resistance and aICW/ht2 was compared to DXA-measured ALM/ht2 by linear regression. In a subset of 61 women, a aICW/ht2 cut-point of 6.5 was chosen as this value captured 70% of women below the published ALM/ht2 cut-point. T-tests were used to compare those below this aICW cut-point, but above ALM (group NS) to the group below the ALM cut-off (group S) and the group above both the ALM and the aICW cut-point (group N).

Participant mean (±SD, range) age was 80.4 years (± 6.1, 70-92) and the mean BMI was 25.8 kg/m2 (± 4.5, 18-44). The average age in the female subgroup was 79.9 years (± 5.9, 70-92) and the BMI was 25.9 kg/m2 (± 4.8, 18-44). aICW and ALM were highly correlated (R2 = 0.78) as were aICW/ht2 and ALM/ht2 (R2 = 0.67) (p < 0.0001). In the women, when applying the EWGSOP DXA ALM sarcopenia cut-point and arbitrarily selecting a comparable aICW limit, 70% with low ALM/ht2 were identified (n = 7), while 10 women were below the aICW cut-off but above the ALM criteria (group NS). These subjects differed from group N, with lower jump power (p = 0.02) and a trend towards lower grip strength (p = 0.056). Furthermore, numerically lower mean values were observed in group NS than group S for gait speed and grip strength.

BIS aICW is highly correlated with DXA-measured ALM directly and when height adjusted. An aICW cut-point of 6.5 identified most (70%) of these women who had low ALM/ht2. Many of the those with low aICW yet above the EWGSOP sarcopenia ALM/ht2 cut-off were lower functioning compared to the non-identified group, suggesting this might represent women with a relatively high DXA measured lean mass, but low muscle mass. These pilot data support further evaluation of BIS as a sarcopenia diagnostic tool. Additionally further studies should include this evaluation in a larger cohort with a wider range of function and determination of, segmental BIS reproducibility.

Neil Binkley

Professor of Medicine
University of Wisconsin School of Medicine and Public Health
Madison, Wisconsin

Bjoern Buehring

Assistant Professor
University of Wisconsin Osteoporosis Clinical Research Programs
Madison, Wisconsin

Diane Krueger

Research Program Manager
University of Wisconsin Osteoporosis Clinical Research Program
Madison, Wisconsin

Diane Krueger received her Bachelor of Science degree at the University of Wisconsin-Madison. She is an ISCD-certified clinical densitometrist and a certified clinical research coordinator through the Association of Clinical Research Professionals. She has been program manager of the University of Wisconsin Osteoporosis Clinical Research Program since its inception in 1993. Ms. Krueger has extensive clinical research experience in osteoporosis and bone densitometry, having coordinated multiple industry and investigator-initiated studies. In collaboration with the UW Osteoporosis Program, she has published over 70 manuscripts and authored or presented over 100 abstracts. Her service with ISCD has included chairing the Technologist Bone Densitometry Update and Annual Meeting Committees, participating on the Education Council, serving on the Executive Committee and Board as member and officer (Secretary and four Presidential seats). She has been Technologist Bone Densitometry Course faculty since 2006.

Yosuke Yamada

National Institutes of Biomedical Innovation, Health and Nutrition
Shinjuku-ku, Tokyo, Japan

Ellen Siglinsky

Research Specialist
University of Wisconsin Osteoporosis Clinical Research Program
Madison, Wisconsin