Creatinine reduction ratio on postoperative day 2 predicts long‐term outcomes after living donor kidney transplantation

Objectives To evaluate the relationship between the creatinine reduction ratio between postoperative days 1 and 2 and post‐transplantation clinical outcomes after living donor kidney transplantation. Methods Clinical data of patients who underwent living donor kidney transplantation at Jichi Medical University Hospital, Tochigi, Japan, between 2006 and 2019 were retrieved. The creatinine reduction ratio between postoperative days 1 and 2 was calculated based on the formula: (Cre1 − Cre2) × 100/Cre1; patients were then classified into either the slow graft function (creatinine reduction ratio between postoperative days 1 and 2 ≤30%) or immediate graft function (creatinine reduction ratio between postoperative days 1 and 2 >30%) group. We carried out the log‐rank test and multivariate Cox proportional hazards regression analyses to assess graft survival and rejection‐free survival, and the unpaired t‐test and multivariate linear regression to assess post‐transplantation estimated glomerular filtration rates. Multivariate analyses used age, sex, dialysis duration, ABO compatibility, donor‐specific antibody positivity and medically complex living donors as explanatory variables. Results Of the 272 patients, 30 and 242 were in the slow graft function and immediate graft function groups, respectively. Multivariate Cox proportional hazards regression analyses showed a significantly higher incidence of overall and death‐censored graft loss in the slow graft function group than the immediate graft function group. The frequency of rejection after 1 week post‐transplantation did not differ within the groups. Post‐transplantation estimated glomerular filtration rates tended to decline earlier in the slow graft function group than in the immediate graft function group; however, the difference was not statistically significant. Conclusions The creatinine reduction ratio between postoperative days 1 and 2 could potentially predict long‐term outcomes after living donor kidney transplantation. Using the creatinine reduction ratio between postoperative days 1 and 2 and other conventional indicators might allow accurate risk classification and appropriate therapeutic interventions.