title: Urine creatinine-based estimates of fat-free mass in community-dwelling older persons: the Rancho Bernardo study.
abstract: OBJECTIVE
  To determine whether a previously developed and externally validated equation using common variables (demographics and weight) that are important determinants of muscle mass to estimate 24-hour urine creatinine excretion rate (eCER) is associated with muscle mass and whether spot urine creatinine (UCr) provides similar estimates of muscle mass.
  
  
  METHODS
  Observational cross-sectional cohort study.
  
  
  METHODS
  The Rancho Bernardo Study, San Diego, California.
  
  
  METHODS
  A total of 1,371 Caucasian, middle class, community-dwelling older adults.
  
  
  METHODS
  Morning spot UCr and fat-free mass (FFM) by dual-energy x-ray absorptiometry were measured. eCER was calculated: eCER (mg/day) = 879.89 + 12.51 × weight (kilogram) - 6.19 × age + 34.51 if black - 379.42 if female. Pearson correlation coefficients and linear regression were used to determine strengths of association of eCER and spot UCr with FFM.
  
  
  RESULTS
  Mean age was 70 years, and 58% were women. eCER was strongly correlated with FFM (r = 0.95, P < .001), a correlation that was superior to that of spot UCr (r = 0.40, P < .001).
  
  
  CONCLUSIONS
  An equation incorporating age, weight, sex, and race to estimate eCER is highly correlated with FFM in community-dwelling older persons and provides a more precise estimate than spot UCr. A simple screening tool for sarcopenia in older persons may allow interventions to maintain or improve muscle mass. Future studies should evaluate whether eCER predicts sarcopenia-related frailty and mortality in older persons.
authors.affiliation: Primary Care Service, VA San Diego Healthcare System, San Diego, California; Division of General Internal Medicine, Department of Medicine, University of California, San Diego, La Jolla, California. Electronic address: sjassal@ucsd.edu.
authors.forename: Simerjot K
authors.initials: SK
authors.lastname: Jassal
authors.affiliation: Division of Epidemiology, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania.
authors.forename: Christina L
authors.initials: CL
authors.lastname: Wassel
authors.affiliation: Division of Epidemiology, Department of Family and Preventive Medicine, University of California, San Diego, La Jolla, California.
authors.forename: Gail A
authors.initials: GA
authors.lastname: Laughlin
authors.affiliation: Division of Epidemiology, Department of Family and Preventive Medicine, University of California, San Diego, La Jolla, California.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Barrett-Connor
authors.affiliation: Division of Nephrology, Department of Medicine, University of California, San Diego, La Jolla, California; Section of Nephrology, Medicine Service, VA San Diego Healthcare System, San Diego, California.
authors.forename: Dena E
authors.initials: DE
authors.lastname: Rifkin
authors.affiliation: Division of Epidemiology, Department of Family and Preventive Medicine, University of California, San Diego, La Jolla, California; Division of Nephrology, Department of Medicine, University of California, San Diego, La Jolla, California; Section of Nephrology, Medicine Service, VA San Diego Healthcare System, San Diego, California.
authors.forename: Joachim H
authors.initials: JH
authors.lastname: Ix
mesh_terms: D000367:Age Factors; D000368:Aged; D001835:Body Weight; D002140:California; D015331:Cohort Studies; D003404:Creatinine / Q000652:urine*; D003430:Cross-Sectional Studies; D005260:Female; D015577:Geriatric Assessment / Q000379:methods*; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal; D015203:Reproducibility of Results; D012737:Sex Factors
chemical_list: D003404:Creatinine