title: Why do preemptive kidney transplant recipients have an allograft survival advantage?
abstract: BACKGROUND
  Preemptive kidney transplantation is associated with an allograft survival advantage and is promoted in part because of this association. The basis for the allograft survival advantage in preemptive recipients is unclear. Possibilities include a lead time bias due to the earlier transplantation of patients with preserved native kidney function, less rapid loss of kidney function after transplantation, or the longer patient survival of preemptive recipients.
  
  
  METHODS
  We compared the glomerular filtration rate (GFR) six months after transplantation and the subsequent rate of loss of kidney function as defined by the annualized change in GFR (mL/min/1.73 m2/year) in 5,966 preemptive and 34,997 non-preemptive recipients. Linear regression methods were applied to serial GFR estimates after transplantation to determine the annualized change in GFR. Multiple regression was used to determine the independent effect of preemptive transplantation upon the annualized change in GFR.
  
  
  RESULTS
  The mean GFR six months after transplantation was similar among preemptive (49.5+/-15.7 mL/min/1.73 m2) and non-preemptive (49.2+/-14.7 mL/min/1.73 m2) recipients (P=0.37). In multivariate analysis, preemptive recipients had a slower decline in GFR (0.28 mL/min/year/1.73 m2; 95% confidence interval 0.11, 0.46; P=0.002). However, this difference was of modest clinical significance and would not explain the allograft survival advantage of preemptive transplantation.
  
  
  CONCLUSIONS
  Neither the preservation of native kidney function nor differences in the rate of loss of kidney function explain the superior allograft survival of preemptive recipients. By exclusion, the allograft survival advantage associated with preemptive transplantation may be due to the longer survival of preemptive recipients.
authors.affiliation: Division of Nephrology, St. Paul's Hospital Vancouver, BC, Canada. jgill@providencehealth.bc.ca
authors.forename: John S
authors.initials: JS
authors.lastname: Gill
authors.forename: Marcello
authors.initials: M
authors.lastname: Tonelli
authors.forename: Nathan
authors.initials: N
authors.lastname: Johnson
authors.forename: Brian J G
authors.initials: BJ
authors.lastname: Pereira
mesh_terms: D000328:Adult; D000368:Aged; D002102:Cadaver; D005260:Female; D005919:Glomerular Filtration Rate / Q000502:physiology*; D006085:Graft Survival / Q000276:immunology*; D006801:Humans; D016030:Kidney Transplantation / Q000276:immunology / Q000401:mortality / Q000502:physiology*; D019520:Living Donors; D008297:Male; D008875:Middle Aged; D018579:Patient Selection; D015996:Survival Rate; D014019:Tissue Donors; D014184:Transplantation, Homologous; D016896:Treatment Outcome