To the Editor:
We are grateful to Safer et al.  for commenting on the methodology used in our recent study , and for defining sarcopenia. The validity of segmental bioelectrical impedance analysis (BIA) for assessing skeletal muscle mass and the significance of low muscle function in the diagnosis of sarcopenia are important issues.
Safer et al. argued that segmental BIA might not be appropriate for measuring muscle mass, referring to two previous papers from Japan and Europe. The BIA system used in these studies is different from that used in our recent study . We used multifrequency BIA with a tetrapolar eight-point tactile electrode system (InBody 720; Biospace, Tokyo, Japan), a newly developed direct segmental multifrequency BIA (DSM-BIA) system. Unlike conventional BIA equipment, which often takes only partial measurements and therefore relies upon formulas to estimate whole body composition, this technique employs the assumption that the human body is composed of five interconnecting cylinders and takes direct impedance measurements from the various body compartments. Of the BIA devices developed over the years, the DSM-BIA system has been thus shown to be superior in the estimation of body composition . Ling et al. recently demonstrated excellent agreement between DSM-BIA and dual energy X-ray absorptiometry (DEXA) for the estimation of lean body mass in both sexes in a large general middle-aged population (n = 484) .
In our recent report, no significant correlations were observed between the skeletal muscle mass and Child-Pugh classification (p = 0.278). To rule out the possibility that BIA overestimated muscle mass in patients with overhydration, including massive ascites and edema, which are often found in patients with Child-Pugh C liver disease, we further divided 74 Child-Pugh C patients into three groups according to the degree of ascites fluid retention (no ascites; 24, mild to moderate ascites; 24, massive ascites; 26), and compared skeletal muscle mass among them. Consequently, skeletal muscle mass in the massive ascites group (92.2 ± 12.2) was significantly lower than that in the no ascites group (102.9 ± 15.5; p = 0.0286; Figure 1). Therefore, the effect of overhydration on overestimation of BIA might be, if any, minimum in using this device, and the deterioration of liver function caused by liver cirrhosis accompanied the decrease in skeletal muscle mass in Child-Pugh C patients. A recent report demonstrating that lean body mass was highly correlated with good method agreement using DEXA as the reference test in 104 stable peritoneal dialysis patients (r = 0.95, p < 0.0001) strongly supports the accuracy of DSM-BIA, even in overhydrated patients . DSM-BIA is superior to DEXA in its simplicity, portability, lower cost, and absence of radiation exposure. Taking these findings into consideration, DSM-BIA can be viewed as the gold standard for assessing sarcopenia.
Evaluation of muscle function, in addition to muscle mass, would indeed be important for diagnosing sarcopenia. As for muscle function in patients undergoing liver transplantation, we are now conducting a prospective study, as described in our recent paper. The interim analysis shows that skeletal muscle mass is strongly correlated with grip strength (data not shown); therefore, misclassification of subjects in our recent report would be, if any, almost negligible.
T. Kaido* and S. Uemoto
Division of Hepato-Biliary-Pancreatic and Transplant Surgery, Department of Surgery, Graduate School of Medicine, Kyoto University, Kyoto, Japan
*Corresponding author: Toshimi Kaido, email@example.com
The authors of this manuscript have no conflicts of interest to disclose as described by the American Journal of Transplantation.