Abstract and Introduction
Abstract
Background: We investigated 10-year trends in deceased donor kidney quality expressed as the kidney donor risk index (KDRI) and subsequent effects on survival outcomes in a European transplant population.
Methods: Time trends in the crude and standardized KDRI between 2005 and 2015 by recipient age, sex, diabetic status and country were examined in 24 177 adult kidney transplant recipients in seven European countries. We determined 5-year patient and graft survival probabilities and the risk of death and graft loss by transplant cohort (Cohort 1: 2005–06, Cohort 2: 2007–08, Cohort 3: 2009–10) and KDRI quintile.
Results: The median crude KDRI increased by 1.3% annually, from 1.31 [interquartile range (IQR) 1.08–1.63] in 2005 to 1.47 (IQR 1.16–1.90) in 2015. This increase, i.e. lower kidney quality, was driven predominantly by increases in donor age, hypertension and donation after circulatory death. With time, the gap between the median standardized KDRI in the youngest (18–44 years) and oldest (>65 years) recipients widened. There was no difference in the median standardized KDRI by recipient sex. The median standardized KDRI was highest in Austria, the Netherlands and the Basque Country (Spain). Within each transplant cohort, the 5-year patient and graft survival probability were higher for the lowest KDRIs. There was no difference in the patient and graft survival outcomes across transplant cohorts, however, over time the survival probabilities for the highest KDRIs improved.
Conclusions: The overall quality of deceased donor kidneys transplanted between 2005 and 2015 has decreased and varies between age groups and countries. Overall patient and graft outcomes remain unchanged.
Introduction
In order to meet the demand for kidneys for transplantation, which continues to exceed the current supply,[1,2] an increasing number of marginal kidneys are being utilized.[3,4] Marginal kidneys have been associated with worse graft survival outcomes.[5] The kidney donor risk index (KDRI), derived from 10 deceased donor factors, provides an estimate of how long a deceased donor kidney allograft can be expected to function relative to the ‘median’ deceased donor kidney retrieved in the USA in the previous calendar year.[6] The KDRI has now been validated in several European countries.[7–9] Lower KDRI scores represent a higher estimated graft survival time, whereas higher KDRI scores represent a lower estimated graft survival time.[10] A deceased kidney donor in 2017 with a standardized KDRI score of 1.5 equates to 1.5 times higher relative risk of allograft failure compared with the ‘median’ deceased donor kidney from 2016. Given that the KDRI is standardized to the median donor of the previous year, the reference group is changing on an annual basis and, as a consequence, a donor represented by a KDRI of 1.5 in 1 year may not be the same as a donor represented by a KDRI of 1.5 in previous years. By standardizing the KDRI over a number of years to the same reference donor, i.e. the median deceased donor in a chosen year, one has a quantitative measure with which to assess the quality of deceased donor kidneys in a given population and across populations over time.
Using data from kidney and transplant registries in seven European countries we investigated the trends in the quality of transplanted deceased donor kidneys between 2005 and 2015, expressed as KDRI scores and standardized to a reference KDRI score. We identified annual trends in standardized KDRI scores over a 10-year period by recipient sex, recipient age group, recipient diabetic status and country of transplantation. Furthermore, we assessed patient and graft survival outcomes by KDRI quintile over time.