Outcomes of Dual Kidney Transplantation from Donors with High Pre-implantation Biopsy Scores

Introduction: The persistent shortage of transplantable kidneys has increased reliance on marginal organs, yet kidneys with advanced chronic lesions on pre-implantation biopsy are frequently discarded. Dual kidney transplantation (DKT) may mitigate this risk by increasing nephron mass, but outcomes of allografts with very high histological scores remain poorly defined. We evaluated kidney transplant outcomes according to transplant type and pre-implantation Karpinski score, with particular focus on DKT using kidneys with combined Karpinski score ≥9. Methods: We conducted a retrospective cohort study of 262 adult deceased-donor kidney transplant recipients undergoing pre-implantation biopsy at a single Italian center between 2014 and 2021. Recipients were stratified into three allocation groups: single kidney transplantation with Karpinski score <9 (SKT <9), DKT with combined Karpinski score <9 (DKT <9), and DKT with combined Karpinski score ≥9 (DKT ≥9). Primary outcomes were post-transplant eGFR and proteinuria during follow-up. Secondary outcomes included delayed graft function (DGF), acute rejection, complications, overall graft failure, all-cause mortality, and death-censored graft failure. Results: Among 262 recipients, 142 received SKT <9, 35 received DKT <9, and 85 received DKT ≥9. DKT donors were older and had higher KDPI/KDRI than SKT donors. Despite greater histological chronicity, recipients of DKT ≥9 grafts did not show inferior renal function at longer-term follow-up, with comparable eGFR and proteinuria at 12 and 36 months. Primary non-function, DGF, biopsy-proven acute rejection, and major complications were similar across groups, although post-transplant thrombotic microangiopathy was more frequent in DKT recipients. Kaplan–Meier analyses showed no significant differences in overall graft failure, all-cause mortality, or death-censored graft failure. In multivariable Cox regression, allocation group was not independently associated with overall graft failure. Conclusion: In this real-world allocation cohort, kidneys with combined Karpinski score ≥9 achieved outcomes comparable to lower-score grafts when allocated as DKT. These findings support the use of DKT as a strategy to safely expand the donor pool and suggest that high histological chronicity should not automatically preclude transplantation when integrated with clinical and functional donor assessment.