Expanding the Kidney Donor Pool
Heidi M. Schaefer, MD
Kidney transplantation has been well-documented to increase survival and improve quality of life over conventional dialysis therapies.
In fact, patients who receive a kidney transplant will live an estimated 10 years longer than they would if they remained on dialysis (N Engl J Med. 1999;341:1725-1730).
Unfortunately, because of considerable and ongoing disparities between supply and demand, most patients with end-stage renal disease (ESRD) will never receive a kidney transplant.
According to United Network for Organ Sharing (UNOS) data, 83,095 candidates are on the active waiting list for kidney transplantation in the United States (www.unos.org/data/, accessed December 21, 2010. And of the 21,423 kidney transplants performed between January and September 2009, 16,520 were from deceased donors and 4,903 from living donors.
The current enduring critical shortage of available organs has led the transplant community to consider strategies to expand the donor pool, both through the use of non-standard-criteria donors and paired live-donor kidney exchange.
Categories of diseased donors
As the clinicians who provide care to ESRD patients eligible for kidney transplant, nephrologists have an obligation to understand the various categories of deceased donors and the respective clinical outcomes associated with each type.
Such understanding will enable us to give transplant candidates sound advice regarding the acceptance of a potential organ. The standard criteria donor (SCD), usually a young person without hypertension or diabetes who fulfills the criteria for brain death, is used as a benchmark against which to measure the efficacy of expanded-criteria donors (ECDs) and donors after cardiac death (DCDs).
ECD kidneys are defined as coming from a donor aged 60 years or older or from a donor aged 50-59 years having two of the following three criteria: (1) death due to cerebrovascular accident, (2) pre-existing hypertension, and (3) terminal serum creatinine greater than 1.5 mg/dL.
An ECD kidney has a 70% greater risk for failure compared with an SCD kidney (Am J Transplant. 2003;3 Suppl 4:114-125). Nevertheless, studies led by Ojo and Stratta (J Am Soc Nephrol. 2001;12:589-597 and Ann Surg. 2004;239:688-697, respectively) as well as others have shown that ECD allograft recipients experience improved survival compared with suitable candidates who remain on dialysis.
This improvement in survival may not be applicable to all patient populations; older patients, nondiabetic patients, recipients of retransplants, and candidates with prolonged wait times benefit most (JAMA. 2005;294:2726-2733 and Am J Transplant. 2007;7:1140-1147).
Another approach has been to use DCDs. These are donors who do not meet the criteria for brain death but whose cardiac function ceased before the organs were procured. Although an increase in delayed graft function (requiring dialysis therapy within the first week of transplantation) has been noted in the previously cited studies by Ojo and Stratta as well as others (Am J Transplant. 2007;7:122-129), DCD kidney recipients have survival comparable to that of SCD kidney recipients.
The availability of both ECD and DCD kidneys has resulted in an increase in the number of deceased donors used for kidney transplantation over the past several years, but significant wait times persist. According to UNOS, the median wait time for transplant in 2004 was 1,219 days.
Another strategy that has emerged as a viable modality and received considerable attention in the media is the use of kidney paired donation (KPD). KPD allows ESRD patients whose live donor is incompatible because of blood type or HLA crossmatch to participate in an exchange of donors.
Two types of exchanges have occurred: “swaps,” in which two or more donor-recipient pairs exchange donors, and “chains,” in which an altruistic donor initiates a series of transplants with the last paired donor in the chain donating a kidney to an unpaired recipient on the deceased-donor waiting list.
Most recently, Rees et al reported a nonsimultaneous, extended altruistic-donor chain (NEAD) that ultimately led to 10 kidney transplants (N Engl J Med. 2009;360:1096-1101). The use of NEAD chains has raised several controversial issues, not the least of which is the possibility that a coregistered donor will back out after his or her recipient has received a transplant. There is also concern about shipping live-donor kidneys from one transplant center to another, generating cold ischemia time that would not have been a factor if both surgeries had occurred at one hospital.
A new pilot program
Despite these issues, multiregional KPD programs have been successful (Transplantation. 2008;86:1744-1748), and simulation studies have shown that a national KPD system would have a significant impact on kidney transplantation (Am J Transplant. 2007;7:2361-2370). In the fall of 2009, UNOS implemented a KPD pilot program involving several experienced centers. The goal of the program was to work through logistical difficulties before rolling out the full system in 2010.
To further inform nephrologists on the expanding options of kidney donation available to their eligible ESRD patients, the Program Committee of the National Kidney Foundation 2010 Spring Clinical Meetings has incorporated two educational sessions into its kidney transplant course.
Entitled “Trends in Kidney Transplantation: What's Hot in 2010,” the course will be offered on April 13, 2010, at the Walt Disney World Swan and Dolphin in Orlando. Nationally recognized experts in the field will discuss patient considerations and who may benefit from the acceptance of non-SCD kidneys.
Of particular interest, Michael A. Rees, MD, PhD, a pioneer in KPD and head of the Alliance for Paired Donation (one of the participants of the UNOS pilot program), will discuss navigation through kidney-exchange programs. A computerized question-and-answer session will enable audience participation, and a spirited and insightful exchange of ideas will be encouraged.
Dr. Schaefer is Assistant Professor of Medicine at Vanderbilt University School of Medicine in Nashville.