Redefining sarcopenia: tomographic muscle mass measurements correlated to urinary creatinine excretion and glomerular filtration rate
Lisa Westenberg1,3, Marcel Zorgdrager2, Tim DA Swaab2, Marco van Londen3, Stephan JL Bakker3, Henri GD Leuvenink1, Alain R Viddeleer2, Robert A Pol1.
1Department of Surgery, Division of Transplant Surgery, University Medical Center Groningen, Groningen, Netherlands; 2Department of Radiology, Medical Imaging Center, University Medical Center Groningen, Groningen, Netherlands; 3Department of Internal Medicine, Division of Nephrology, University Medical Center Groningen, Groningen, Netherlands
Introduction: Determining the presence of sarcopenia is important when assessing whether a patient is fit for surgery. Imaging with computed tomography (CT) has proven to be one of the most accurate and objective methods for assessment of muscle mass, but consensus on cut-off values for sarcopenia is lacking. The purposes of this study were to assess age-, sex-, and body mass index (BMI)-specific reference values of muscle mass in a large healthy Caucasian population and to correlate skeletal muscle index (SMI) to 24-hour urinary creatine excretion rate (24-hr UCE), estimated glomerular filtration rate (eGFR), and measured glomerular filtration rate (mGFR).
Methods: Between 2002 and 2019, 964 healthy subjects from the University Medical Center Groningen were included in this study. Skeletal muscle area (SMA) was determined from an axial CT slice at vertebral level L3 and included psoas, paraspinal and abdominal wall muscles. SMA, SMI and skeletal muscle radiation attenuation (SMRA) were analysed and subsequently age-, sex- and BMI-specific reference values were calculated. SMI was correlated to 24-hr UCE, eGFR and mGFR.
Results: Mean subject age was 53 ± 11 years and 50% were male. Subjects were stratified by sex and age. The reference values for low muscle mass (calculated as two standard deviations below the mean) of SMI in males were 38.8 cm2/m2 for 20-29 years, 39.2 for 30-39 years, 39.9 for 40-49 years, 39.0 for 50-59 years, 37.0 for 60-69 years, and 36.8 for 70-79 years. For females, reference values of SMI were 37.5 cm2/m2 for 20-29 years, 35.5 for 30-39 years, 32.8 for 40-49 years, 33.2 for 50-59 years, 31.3 for 60-69 years, and 31.5 for 70-79 years. 24-hr UCE and SMI were significantly correlated (r = 0.54, p < 0.001) and Bland-Altman plot showed no bias between these two methods of assessing muscle mass (mean = 0.001, SD = 0.95, p = 0.98). eGFR showed no statistically significant correlation with SMI, but SMI and mGFR were positively correlated, r = 0.46 p <0.001.
Conclusion: This study provides age-, sex-, and BMI-specific reference values for skeletal muscle parameters at level L3, that can be used as reference data in clinical practice and future studies assessing the presence of sarcopenia. It also shows a strong, positive correlation between CT derived SMI values and 24-hr UCE.
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