title: Worsening renal function defined as an absolute increase in serum creatinine is a biased metric for the study of cardio-renal interactions.
abstract: OBJECTIVE
  Worsening renal function (WRF) during the treatment of decompensated heart failure, frequently defined as an absolute increase in serum creatinine >or=0.3 mg/dl, has been reported as a strong adverse prognostic factor in several studies. We hypothesized that this definition of WRF is biased by baseline renal function secondary to the exponential relationship between creatinine and renal function.
  
  
  METHODS
  We reviewed consecutive admissions with a discharge diagnosis of heart failure. An increase in creatinine >or=0.3 mg/dl (WRF(CREAT)) was compared to a decrease in GFR >or=20% (WRF(GFR)).
  
  
  RESULTS
  Overall, 993 admissions met eligibility. WRF(CREAT) occurred in 31.5% and WRF(GFR) in 32.7%. WRF(CREAT) and WRF(GFR) had opposing relationships with baseline renal function (OR = 1.9 vs. OR = 0.51, respectively, p < 0.001). Both definitions had similar unadjusted associations with death at 30 days [WRF(GFR) OR = 2.3 (95% CI 1.1-4.8), p = 0.026; WRF(CREAT) OR = 2.1 (95% CI 1.0-4.4), p = 0.047]. Controlling for baseline renal insufficiency, WRF(GFR) added incrementally in the prediction of mortality (p = 0.009); however, WRF(CREAT) did not (p = 0.11).
  
  
  CONCLUSIONS
  WRF, defined as an absolute change in serum creatinine, is heavily biased by baseline renal function. An alternative definition of WRF should be considered for future studies of cardio-renal interactions.
authors.affiliation: Department of Medicine, Cardiovascular Division, University of Pennsylvania, Philadelphia, Pa., USA. jeffrey.testani@uphs.upenn.edu
authors.forename: Jeffrey M
authors.initials: JM
authors.lastname: Testani
authors.forename: Brian D
authors.initials: BD
authors.lastname: McCauley
authors.forename: Jennifer
authors.initials: J
authors.lastname: Chen
authors.forename: Michael
authors.initials: M
authors.lastname: Shumski
authors.forename: Richard P
authors.initials: RP
authors.lastname: Shannon
mesh_terms: D000368:Aged; D003404:Creatinine / Q000097:blood*; D005260:Female; D005919:Glomerular Filtration Rate; D006333:Heart Failure / Q000097:blood / Q000150:complications* / Q000628:therapy; D006785:Hospitals, University; D006801:Humans; D007668:Kidney / Q000503:physiopathology*; D007674:Kidney Diseases / Q000097:blood* / Q000150:complications / Q000401:mortality; D007677:Kidney Function Tests / Q000592:standards*; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D010414:Pennsylvania / Q000453:epidemiology; D011379:Prognosis
chemical_list: D003404:Creatinine