title: Predicting the glomerular filtration rate in bariatric surgery patients.
abstract: OBJECTIVE
  Identifying the best method to estimate the glomerular filtration rate (GFR) in bariatric surgery patients has important implications for the clinical care of obese patients and research into the impact of obesity and weight reduction on kidney health. We therefore performed such an analysis in patients before and after surgical weight loss.
  
  
  METHODS
  Fasting measured GFR (mGFR) by plasma iohexol clearance before and after bariatric surgery was obtained in 36 severely obese individuals. Estimated GFR was calculated using the Modification of Diet in Renal Disease equation, the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation using serum creatinine only, the CKD-EPI equation using serum cystatin C only and a recently derived equation that uses both serum creatinine and cystatin C (CKD-EPIcreat-cystC) and then compared to mGFR.
  
  
  RESULTS
  Participants were primarily middle-aged white females with a mean baseline body mass index of 46 ± 9, serum creatinine of 0.81 ± 0.24 mg/dl and mGFR of 117 ± 40 ml/min. mGFR had a stronger linear relationship with inverse cystatin C before (r = 0.28, p = 0.09) and after (r = 0.38, p = 0.02) surgery compared to the inverse of creatinine (before: r = 0.26, p = 0.13; after: r = 0.11, p = 0.51). mGFR fell by 17 ± 35 ml/min (p = 0.007) following surgery. The CKD-EPIcreat-cystC was unquestionably the best overall performing estimating equation before and after surgery, revealing very little bias and a capacity to estimate mGFR within 30% of its true value over 80% of the time. This was true whether or not mGFR was indexed for body surface area.
  
  
  CONCLUSIONS
  In severely obese bariatric surgery patients with normal kidney function, cystatin C is more strongly associated with mGFR than is serum creatinine. The CKD-EPIcreat-cystC equation best predicted mGFR both before and after surgery.
authors.affiliation: Department of Medicine, Indiana University School of Medicine, Indianapolis, Ind., USA.
authors.forename: Allon N
authors.initials: AN
authors.lastname: Friedman
authors.forename: Sharon
authors.initials: S
authors.lastname: Moe
authors.forename: William F
authors.initials: WF
authors.lastname: Fadel
authors.forename: Margaret
authors.initials: M
authors.lastname: Inman
authors.forename: Samer G
authors.initials: SG
authors.lastname: Mattar
authors.forename: Zak
authors.initials: Z
authors.lastname: Shihabi
authors.forename: Sara K
authors.initials: SK
authors.lastname: Quinney
mesh_terms: D000328:Adult; D050110:Bariatric Surgery / Q000379:methods*; D001830:Body Surface Area; D001835:Body Weight; D003404:Creatinine / Q000097:blood; D055316:Cystatin C / Q000097:blood; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007472:Iohexol / Q000032:analysis; D007668:Kidney / Q000502:physiology; D007677:Kidney Function Tests; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000601:surgery*; D051436:Renal Insufficiency, Chronic / Q000150:complications
chemical_list: D055316:Cystatin C; D007472:Iohexol; D003404:Creatinine