title: A New Equation to Estimate Muscle Mass from Creatinine and Cystatin C.
abstract: BACKGROUND
  With evaluation for physical performance, measuring muscle mass is an important step in detecting sarcopenia. However, there are no methods to estimate muscle mass from blood sampling.
  
  
  METHODS
  To develop a new equation to estimate total-body muscle mass with serum creatinine and cystatin C level, we designed a cross-sectional study with separate derivation and validation cohorts. Total body muscle mass and fat mass were measured using dual-energy x-ray absorptiometry (DXA) in 214 adults aged 25 to 84 years who underwent physical checkups from 2010 to 2013 in a single tertiary hospital. Serum creatinine and cystatin C levels were also examined.
  
  
  RESULTS
  Serum creatinine was correlated with muscle mass (P < .001), and serum cystatin C was correlated with body fat mass (P < .001) after adjusting glomerular filtration rate (GFR). After eliminating GFR, an equation to estimate total-body muscle mass was generated and coefficients were calculated in the derivation cohort. There was an agreement between muscle mass calculated by the novel equation and measured by DXA in both the derivation and validation cohort (P < .001, adjusted R2 = 0.829, β = 0.95, P < .001, adjusted R2 = 0.856, β = 1.03, respectively).
  
  
  CONCLUSIONS
  The new equation based on serum creatinine and cystatin C levels can be used to estimate total-body muscle mass.
authors: Department of Internal Medicine, Seoul National University Bundang Hospital, Seongnam, Republic of Korea.|Seoul National University College of Medicine, Seoul, Republic of Korea.
authors: Sun-wook
authors: SW
authors: Kim
authors: Department of Internal Medicine, Seoul National University Bundang Hospital, Seongnam, Republic of Korea.|Graduate School of Medical Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon, Republic of Korea.
authors: Hee-Won
authors: HW
authors: Jung
authors: Department of Internal Medicine, Seoul National University Bundang Hospital, Seongnam, Republic of Korea.|Seoul National University College of Medicine, Seoul, Republic of Korea.
authors: Cheol-Ho
authors: CH
authors: Kim
authors: Department of Internal Medicine, Seoul National University Bundang Hospital, Seongnam, Republic of Korea.|Seoul National University College of Medicine, Seoul, Republic of Korea.
authors: Kwang-il
authors: KI
authors: Kim
authors: Department of Internal Medicine, Seoul National University Bundang Hospital, Seongnam, Republic of Korea.|Seoul National University College of Medicine, Seoul, Republic of Korea.
authors: Ho Jun
authors: HJ
authors: Chin
authors: Seoul National University College of Medicine, Seoul, Republic of Korea.|Department of Internal Medicine, Seoul National University Hospital, Seoul, Republic of Korea.
authors: Hajeong
authors: H
authors: Lee
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods; D000273:Adipose Tissue / Q000502:physiology; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003404:Creatinine / Q000097:blood*; D003430:Cross-Sectional Studies; D055316:Cystatin C / Q000097:blood*; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000502:physiology*; D012189:Retrospective Studies; D055948:Sarcopenia / Q000097:blood
chemical_list: D055316:Cystatin C; D003404:Creatinine