title: Serum creatinine and functional limitation in elderly persons.
abstract: BACKGROUND
  Creatinine is a commonly used measure of kidney function, but serum levels are also influenced by muscle mass. We hypothesized that higher serum creatinine would be associated with self-reported functional limitation in community-dwelling elderly.
  
  
  METHODS
  Subjects (n = 1,553) were participants in the Study of Physical Performance and Age-Related Changes in Sonomans, a cohort to study aging and physical function. We explored three strategies to account for the effects of muscle mass on serum creatinine.
  
  
  RESULTS
  We observed a J-shaped association of creatinine with functional limitation. Above the study-specific mean creatinine (0.97 mg/dL in women and 1.15 mg/dL in men), the unadjusted odds ratio of functional limitation per standard deviation (0.20 mg/dL in women and 0.23 mg/dL in men) higher creatinine was 2.27 (95% confidence interval [CI] 1.75-2.94, p < .001) in women and 1.42 (95% CI 1.12-1.80, p = .003) in men. This association was inverted in persons with creatinine levels below the mean. Adjustment for muscle mass did not have an important effect on the association between creatinine and functional limitation. These associations remained after multivariable adjustment for demographics and health conditions but were statistically significant only in women.
  
  
  CONCLUSIONS
  In elderly adults, higher creatinine levels are associated with functional limitation, consistent with prior literature that has demonstrated reduced physical performance in persons with kidney disease. However, the association of low creatinine levels with functional limitation suggests that creatinine levels are influenced by factors other than kidney function and muscle mass in the elderly.
authors.affiliation: Department of Epidemiology, School of Public Health, University of California, Berkeley, USA. michelleodden@berkeley.edu
authors.forename: Michelle C
authors.initials: MC
authors.lastname: Odden
authors.forename: Michael G
authors.initials: MG
authors.lastname: Shlipak
authors.forename: Ira B
authors.initials: IB
authors.lastname: Tager
mesh_terms: D000203:Activities of Daily Living; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D015415:Biomarkers / Q000097:blood; D015992:Body Mass Index; D015331:Cohort Studies; D016001:Confidence Intervals; D003404:Creatinine / Q000097:blood*; D003430:Cross-Sectional Studies; D005260:Female; D006304:Health Status; D006801:Humans; D007677:Kidney Function Tests; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D051346:Mobility Limitation; D009043:Motor Activity; D016017:Odds Ratio; D011336:Probability; D012307:Risk Factors; D012680:Sensitivity and Specificity; D012737:Sex Factors
chemical_list: D015415:Biomarkers; D003404:Creatinine