Background: Proteinuria in kidney transplant recipients (KTRs) is known to be associated with poor patient and allograft survival. However, the relationship between urinary protein to creatinine ratio (uPCR) or urinary albumin to creatinine ratio (uACR) during the early postoperative period and renal outcome of KTRs is yet to be determined.
Methods: This single center retrospective cohort study included 353 KTRs who underwent kidney transplantation (KT) from 2014 to 2017 and followed up for 1 year or more: living donor KT in 186 KTRs and deceased donor KT (DDKT) in 167 KTRs. Postoperative uPCR and uACR were measured during the immediate postoperative period (< postoperative 7 days) and on postoperative 2-3 weeks as well as 3-6 months. The primary outcome was estimated glomerular filtration rate (eGFR) at 1 year after KT: high eGFR group ≥ 60 mL/min/1.73 m² and low eGFR group < 60 mL/min/1.73 m². The secondary outcome was the incidence of delayed graft function (DGF) in DDKT recipients.
Results: Compared to the low eGFR group, the high eGFR group showed lower uPCR (median [IQR]: 810 [178 - 500] vs. 1220 [640 – 3900] ㎍/㎎Cr; p = 0.007) and lower uACR (342 [165 - 976] vs. 613 [288 - 2509] ㎍/㎎Cr; p = 0.002) during the immediate postoperative period. DDKT recipients with uPCR ≥ 3000 -㎍/㎎Cr during the immediate postoperative period was associated with higher incidence of DGF (DDKT recipients with uPCR < 3000 -㎍/㎎Cr vs. those with uPCR ≥ 3000 -㎍/㎎Cr, 13% vs. 30% [odds ratio 2.87]; p = 0.007), and lower eGFR before discharge (75 [56 – 92] vs. 60 [41 – 84]mL/min/1.73 m2; p = 0.001) compared to KTRs with uPCR < 3000 ㎍/㎎Cr. Linear logistic regression analysis showed that KTRs with higher uPCR at postoperative 3-6 months showed lower eGFR at 1 year after KT. Rejection within 6 months and higher uPCR at postoperative 3-6 months were identified as predictors of low eGFR at 1 year after KT.
Conclusions: Our results suggest that uPCR during the immediate postoperative period and postoperative 3 - 6 months may be potential predictors of post-KT 1 year renal outcome.