title: The relative effects of fat versus muscle mass on cystatin C and estimates of renal function in healthy young men.
abstract: BACKGROUND
  It is well known that plasma creatinine concentration is affected by muscle mass, while some studies have suggested cystatin C is affected by body mass index (BMI). Our aim was to assess the effects of lean versus fat mass on cystatin C and creatinine derivative equations in estimating glomerular filtration rate (GFR) in healthy young men.
  
  
  METHODS
  Three groups of participants were studied: those classified as normal (BMI 18-25 kg/m(2) with body fat <30%); muscular subjects (BMI >30 kg/m(2) and body fat <20%); and obese subjects (BMI >30 kg/m(2) and body fat >30%). All underwent diethylenetriamine pentaacetic acid GFR, bio-electrical impedance and dual-energy X-ray absorptiometry body composition analysis, measurement of plasma cystatin C, creatinine and high-sensitivity C-reactive protein and completed a diet record.
  
  
  RESULTS
  Cystatin C was highest in the obese group (0.77 mg/L; 95% confidence intervals [CI] 0.69-0.77) and creatinine was highest in the muscular group (90.1 μmol/L; 95% CI 84.3-96.0). On multivariate analysis, body fat and GFR (P = 0.003) were significant determinants of cystatin C; muscle mass and age affected creatinine significantly (P = 0.02). Using cystatin C equations, Le Bricon and Hoek showed significantly lower estimated GFR in the obese group but performed reasonably well within 50%, 30% and 20% of GFR. Creatinine equations showed significant underestimations of GFR for the muscular group.
  
  
  CONCLUSIONS
  Body fat is a significant determinant of cystatin C while creatinine concentration is highly affected by muscle mass and age. Body composition plays an important role in the interpretation of renal function. Cystatin C equations are still accurate in predicting GFR in our healthy male group without chronic kidney disease.
authors.affiliation: Biochemistry Department, Medlab South Ltd, PO Box 25-091, Christchurch 8013, New Zealand.
authors.forename: Janice S C
authors.initials: JS
authors.lastname: Chew-Harris
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Florkowski
authors.forename: Peter M
authors.initials: PM
authors.lastname: George
authors.forename: Jane L
authors.initials: JL
authors.lastname: Elmslie
authors.forename: Zoltan H
authors.initials: ZH
authors.lastname: Endre
mesh_terms: D015502:Absorptiometry, Photon; D000273:Adipose Tissue / Q000502:physiology*; D000293:Adolescent; D000328:Adult; D001823:Body Composition; D015992:Body Mass Index; D002097:C-Reactive Protein / Q000032:analysis; D003404:Creatinine / Q000097:blood*; D055316:Cystatin C / Q000097:blood*; D017097:Electric Impedance; D005919:Glomerular Filtration Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000502:physiology*; D009765:Obesity / Q000097:blood* / Q000503:physiopathology; D004369:Pentetic Acid
chemical_list: D055316:Cystatin C; D004369:Pentetic Acid; D002097:C-Reactive Protein; D003404:Creatinine