"Long-term effects of center volume on transplant outcomes in adult kidney transplant recipients"

Abstract

Background: The influence of center volume on kidney transplant outcomes is a topic of ongoing debate. In this study, we employed competing risk analyses to accurately estimate the marginal probability of graft failure in the presence of competing events, such as mortality from other causes with long-term outcomes. The incorporation of immunosuppression protocols and extended follow-up offers additional insights. Our emphasis on long-term follow-up aligns with biological considerations where competing risks play a significant role.

Methods: We examined data from 219,878 adult kidney-only transplantations across 256 U.S. transplant centers (January 2001-December 2015) sourced from the Organ Procurement and Transplantation Network registry. Centers were classified into quartiles by annual volume: low (Q1 = 28), medium (Q2 = 75), medium-high (Q3 = 121), and high (Q4 = 195). Our study investigated the relationship between center volume and 5-year outcomes, focusing on graft failure and mortality. Sub-population analyses included deceased donors, living donors, diabetic recipients, those with kidney donor profile index >85%, and re-transplants from deceased donors.

Results: Adjusted cause-specific hazard ratios (aCHR) for Five-Year Graft Failure and Patient Death were examined by center volume, with low-volume centers as the reference standard (aCHR: 1.0). In deceased donors, medium-high and high-volume centers showed significantly lower cause-specific hazard ratios for graft failure (medium-high aCHR = 0.892, p<0.001; high aCHR = 0.953, p = 0.149) and patient death (medium-high aCHR = 0.828, p<0.001; high aCHR = 0.898, p = 0.003). Among living donors, no significant differences were found for graft failure, while a trend towards lower cause-specific hazard ratios for patient death was observed in medium-high (aCHR = 0.895, p = 0.107) and high-volume centers (aCHR = 0.88, p = 0.061).

Conclusion: Higher center volume is associated with significantly lower cause-specific hazard ratios for graft failure and patient death in deceased donors, while a trend towards reduced cause-specific hazard ratios for patient death is observed in living donors.

Fig 1

Cause-specific survival rates of patient death (solid lines) not from kidney graft failure and graft failure (dotted lines) by center volume groups (low, medium, medium-high and high-volume centers) for: (A) Deceased donors: Five-Year Graft Survival was 84.15% for low-volume, 83.36% for medium volume, 84.73% for medium-high volume, and 83.25% for high-volume centers. Five-Year Patient Survival was 86.43% for low-volume, 87.33% for medium volume, 88.65% for medium-high volume, and 86.71% for high-volume centers. (B) Living donors: Five-Year Graft Survival was 89.68% for low-volume, 90.39% for medium volume, 90.89% for medium-high volume, and 90.48% for high-volume centers. Five-Year Patient Survival was 92.89% for low-volume, 93.30% for medium volume, 93.66% for medium-high volume, and 93.17% for high-volume centers. (C) Diabetic patients: Five-Year Graft Survival was 86.44% for low-volume, 86.11% for medium volume, 87.59% for medium-high volume, and 87.32% for high-volume centers. Five-Year Patient Survival was 82.25% for low-volume, 82.55% for medium volume, 84.75% for medium-high volume, and 83.75% for high-volume centers. (D) KDPI > 85%: Five-Year Graft Survival was 73.52% for low-volume, 71.08% for medium volume, 74.13% for medium-high volume, and 73.04% for high-volume centers. Five-Year Patient Survival was 75.97% for low-volume, 76.60% for medium volume, 80.91% for medium-high volume, and 79.31% for high-volume centers. (E) Re-transplants: Five-Year Graft Survival was 81.76% for low-volume, 80.43% for medium volume, 82.33% for medium-high volume, and 79.88% for high-volume centers. Five-Year Patient Survival was 89.21% for low-volume, 89.25% for medium volume, 89.98% for medium-high volume, and 88.95% for high-volume centers.

Fig 2

Forest Plots for Patient Outcomes Stratified by Center Volume: (A) Adjusted Cause-specific hazard ratios (aCHR) for Five-Year Graft Failure by CRA. Low volume center is reference standard (HR: 1.0). Deceased Donors: Medium-volume aCHR = 1.0005 (95%CI = 0.950–1.063; p = 0.863), Medium-high volume aCHR = 0.892 (95%CI = 0.841–0.946; p<0.001), High-volume aCHR = 0.953 (95%CI = 0.893–1.017; p = 0.149); Living Donors: Medium-volume aCHR = 0.968 (95%CI = 0.860–1.089; p = 0.589), Medium-high volume aCHR = 0.897 (95%CI = 0.796–1.012; p = 0.077), High-volume aCHR = 0.90 (95%CI = 0.798–1.014; p = 0.085); Diabetic Patients: Medium-volume aCHR = 0.96 (95%CI = 0.871–1.058; p = 0.406), Medium-high volume aCHR = 0.848 (95%CI = 0.768–0.936; p = 0.001), High-volume aCHR = 0.881 (95%CI = 0.787–0.986; p = 0.027); KDPI>85% donors: Medium-volume aCHR = 1.096 (95%CI = 0.914–1.314; p = 0.325), Medium-high volume aCHR = 0.999 (95%CI = 0.832–1.2; p = 0.992), High-volume aCHR = 0.997 (95%CI = 0.813–1.221; p = 0.974); Re-transplants: Medium-volume aCHR = 1.052 (95%CI = 0.904–1.224; p = 0.513), Medium-high volume aCHR = 0.969 (95%CI = 0.83–1.131; p = 0.686), High-volume aCHR = 1.101 (95%CI = 0.937–1.294; p = 0.241); (B) Adjusted Cause-specific hazard ratios (aCHR) for Five-Year Patient Death by CRA. Low volume center is reference standard (HR: 1.0). Deceased Donors: Medium-volume aCHR = 0.956 (95%CI = 0.899–1.017; p = 0.157), Medium-high volume aCHR = 0.828 (95%CI = 0.776–0.884; p<0.001), High-volume aCHR = 0.898 (95%CI = 0.836–0.965; p = 0.003); Living Donors: Medium-volume aCHR = 1.006 (95%CI = 0.881–1.150; p = 0.925), Medium-high volume aCHR = 0.895 (95%CI = 0.0.781–1.024; p = 0.107), High-volume aCHR = 0.88 (95%CI = 0.77–1.006; p = 0.061); Diabetic Patients: Medium-volume aCHR = 0.964 (95%CI = 0.885–1.05; p = 0.396), Medium-high volume aCHR = 0.826 (95%CI = 0.755–0.905; p<0.001), High-volume aCHR = 0.928 (95%CI = 0.84–1.025; p = 0.14); KDPI>85% donors: Medium-volume aCHR = 0.981 (95%CI = 0.813–1.182; p = 0.838), Medium-high volume aCHR = 0.776 (95%CI = 0.64–0.941; p = 0.01), High-volume aCHR = 0.787 (95%CI = 0.634–0.977; p = 0.03); Re-transplants: Medium-volume aCHR = 0.989 (95%CI = 0.812–1.204; p = 0.91), Medium-high volume aCHR = 0.94 (95%CI = 0.77–1.149; p = 0.548), High-volume aCHR = 0.963 (95%CI = 0.777–1.193; p = 0.73).