Abstract and Introduction
The Organ Procurement and Transplant Network (OPTN) implemented a new heart allocation policy on October 18, 2018. Published estimates of lower posttransplant survival under the new policy in cohorts with limited follow-up may be biased by informative censoring. Using the Scientific Registry of Transplant Recipients, we used the Kaplan–Meier method to estimate 1-year posttransplant survival for pre-policy (November 1, 2016, to October 31, 2017) and post-policy cohorts (November 1, 2018, to October 31, 2019) with follow-up through March 2, 2021. We adjusted for changes in recipient population over time with a multivariable Cox proportional hazards model. To demonstrate the effect of inadequate follow-up on post-policy survival estimates, we repeated the analysis but only included follow-up through October 31, 2019. Transplant programs transplanted 2594 patients in the pre-policy cohort and 2761 patients in the post-policy cohort. With follow-up through March 2, 2021, unadjusted 1-year posttransplant survival was 90.6% (89.5%–91.8%) in the pre-policy cohort and 90.8% (89.7%–91.9%) in the post-policy cohort (adjusted HR = 0.93 [0.77–1.12]). Ignoring follow-up after October 31, 2019, the post-policy estimate was biased downward (1-year: 82.2%). When estimated with adequate follow-up, 1-year posttransplant survival under the new heart allocation policy was not significantly different.
The Organ Procurement and Transplantation Network (OPTN) implemented a new donor heart allocation policy on October 18, 2018. Studies evaluating the impact of this new policy on posttransplant survival contain discrepant findings. Five reports found decreased posttransplant survival under the new policy,[2–6] and two reports found no difference in posttransplant survival.[7,8] Notably, the studies with lower estimates of posttransplant survival in the post-policy era have significantly fewer follow-up observations of post-policy recipients compared with the studies finding unchanged survival.
One proposed explanation for the conflicting results is informative censoring bias. A fundamental assumption of the Kaplan–Meier survival estimator is that censoring is statistically independent of survival time. If censored patients have longer survival times than non-censored patients, the Kaplan–Meier estimator can be biased downward. Transplant programs are required to report recipient deaths faster than routine follow-up appointments for healthy recipients. If a study's data are heavily censored, this differential data submission requirement based on recipient survival status could lead to a lower Kaplan–Meier estimate than the true population survival rate. Studies that reported lower estimates of posttransplant survival in the post-policy era[2–6] have significantly more censoring in their post-policy cohorts than the studies finding unchanged survival.[7,8]
This study uses more complete recipient follow-up data to evaluate the hypothesis that informative censoring biased the estimates of lower posttransplant survival in the new heart allocation system.
American Journal of Transplantation. 2022;22(6):1683-1690. © 2022 Blackwell Publishing