Over the past two decades there have been dramatic declines in rates of acute rejection and allograft failures that occur in the first 3–6 months after kidney transplantation (1). These gains in early outcomes have made future improvements more dependent on reductions in the rate of late allograft failure. Whether there has been significant improvement in the rate of late allograft failures is controversial. Using data from the United Network for Organ Sharing (UNOS), Hariharan and colleagues reported substantial improvements in the projected half-lives of kidney allografts, a measure of late allograft failure (2). Subsequently, Meier-Kriesche and colleagues reported that there has been little or no improvement in actual late graft failure (3). These two studies examined transplants carried out on or before 1995.
Few would argue that reducing the rate of late allograft failure depends on maintaining stable allograft function. Surprisingly, few studies have examined long-term kidney function in large numbers of unselected transplant recipients. Single centers rarely have sufficient data, and registry data rarely provide enough detail for accurate assessment of post-transplant function. The UNOS registry, for example, does not record the date the function was assessed, but reports only the ‘last known’ serum creatinine. In the current study, we pooled data from five centers in North America (each of which maintains close, long-term, patient follow-up) to examine trends in long-term kidney allograft function. Specifically, we hypothesized that there has been an improvement in the rate of decline in long-term kidney allograft function over the past two decades (4).