Feasibility and Accuracy of Bioelectric Impedance Analysis in Estimating Skeletal Muscle Mass in Older Adults with Multiple Myeloma
Authors: Doshi Apoorva , Tucker Abigail , Ravi Gayathri , Bal Susan , Godby Kelly , Evans William , Shankaran Mahalakshmi Shubha , Costa Luciano J. , Williams Grant , Bhatia Smita , Giri Smith 
Published: December 2024

Introduction:
Sarcopenia, the loss of muscle mass and function, is associated with worse outcomes in older adults with cancer. Patients with sarcopenia may benefit from targeted interventions, making accurate assessment of skeletal muscle mass (SMM) crucial. Bioelectric impedance analysis (BIA) is a low-cost method for estimating SMM in older adults. It can be conveniently administered in a clinical setting or at the bedside, offering a practical alternative to more expensive imaging options such as full-body MRI or DEXA scan. Our study aimed to assess the feasibility and accuracy of BIA for estimating SMM in older adults with multiple myeloma (MM) by comparing it with the D3-creatine dilution (D3Cr) method (Shankaran et al JCSM 2018; used as a gold standard).
Methods:
We included older adults (≥ 60 years (y) at diagnosis) with MM undergoing autologous hematopoietic stem cell transplantation at a single institution enrolled in a prospective study. All participants underwent baseline (pre-transplant time point) SMM estimation using the D3Cr method. Participants also underwent BIA on the same day using a single frequency (50 kHz) impedance device (Quantum IV, RJL Systems, MI, USA) with SMM estimated using Sergi's equation, as recommended by the European Working Group on Sarcopenia.
We conducted Bland-Altman analysis to assess and quantify the agreement between the two methods. The differences between the measurements obtained by the two methods were calculated for each patient. The mean difference (MD) was determined, and the standard deviation (SD) of these differences was computed. The limits of agreement (LoA) were defined as the MD ± 1.96 times the SD of the differences. A conservative clinical threshold for an acceptable difference in SMM estimation between the two methods was set at LoA ≤ ±5 kg.
Outlier analysis was performed to understand the variability by reviewing patient charts, imaging reports, and comparing baseline characteristics. A sensitivity analysis was conducted to evaluate if using an alternate BIA equation (Kyle's equation) improved the agreement.
Results:
Of the 43 patients eligible for analysis, 32 (74%) underwent SMM assessments using both BIA and D3Cr methods; 11 (26%) could not undergo BIA analysis, due to the presence of metal hardware in either the spine or both the sides of the body, as per the manufacturer's recommendations. The median age at diagnosis of MM was 66 (IQR: 63 - 70) y; 72% were men, 75% were non-Hispanic Whites, 28% had International Staging System stage 3 and 28% had high risk cytogenetics. The median BMI was 28.2 (IQR: 26.1-32.1) kg/m2 and the median SMM using D3Cr was 30.47 (IQR 22.35-34.38) kg.
As per Bland-Altman analysis, the MD in SMM estimation between BIA and D3Cr was -4.55 kg [LoA: -19.76 kg to 10.66 kg]. Outlier analysis did not identify any systematic differences between outliers and others based on observable characteristics including renal function, BMI and presence of metal hardware. Upon changing the equation to Kyle's equation, the MD was -6.00 kg [LoA: - 20.94 kg to 8.94 kg].
Conclusion:
Our study demonstrated that BIA is not a feasible and accurate option for SMM estimation compared to D3Cr due to a number of reasons. Around one in four patients could not undergo BIA due to contraindications arising from presence of implanted metal hardware in the body. Additionally, Bland-Altman analysis comparing BIA and D3Cr revealed wide limits of agreement which were well outside the clinically acceptable range. Consequently, while BIA is a low-cost and easily administered method, it lacks sufficient clinical utility for accurate SMM estimation compared to the D3Cr method in older adults with MM.