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Excess demand for donor organs has stimulated nationally organized efforts to maximize organ donation. With respect to deceased donation, Spain has served as the benchmark.[1, 2] For example, in the year 1999, Spain boasted the highest deceased donor rate of 33.6 donors per million population (pmp), which was 57% higher than the US rate of 21.5 donors pmp.
Although the number of deceased donors available for transplantation is ultimately limited by the death rate of the population, only a fraction of deaths eventually result in successful donation, and the limitations to increased donation must be closely examined in each particular system. For example, a particular donor system may be limited by cultural, experiential, legal, or logistical factors. One example of a predominantly cultural limitation exists in Japan, where popular religious beliefs have retarded the development of deceased donor transplantation despite a medically advanced culture. In contrast, Spain, aided by a centrally organized effort, has created a culture favorable for donation, which includes presumed consent legislation as well as efficient protocols for the identification, referral, and management of potential organ donors.
When a donation system overcomes structural barriers, the primary factor limiting donation becomes donor quality as perceived within a transplant community. Donation systems have classically been measured by the number of donors pmp. It is obvious that organ utilization is an important aspect of this measure, and usage is dependent on the perceived quality of the organ versus the perceived need.
Although donor quality encompasses a wide variety of factors, advanced donor age is a pervasive risk factor influencing organ quality and utilization.[6, 7] Although outcomes are generally poorer, the recent achievement of acceptable outcomes has allowed the progressive expansion of the donor pool to include a larger portion of older donors.[8-10]
A prior comparative analysis of deceased donor utilization rates in Spain and the United States concluded that the primary difference accounting for the rapid growth of donation in Spain in the decade from 1989 to 1999 was Spain's rapid acceptance of older transplant donors. For example, in 1999, donors older than 60 years constituted 30.3% of the donor population in Spain but only 13.3% in the United States. This follow-up study compares the US and Spanish donor experiences for the following decade (1999-2009) with the aim of better understanding the implications of the Spanish experience for increasing the donation rate in the United States.
MATERIALS AND METHODS
Data for the analysis were derived from publicly available archives and previously published reports. Data for deceased donor organ activity in Spain were obtained from the National Transplant Organization Web site,13 and data from the US Scientific Registry of Transplant Recipients were requested. Population estimates for United Network for Organ Sharing (UNOS) regions were derived from publicly available US Census population estimates for individual states. Data for US consent rates for organ donation and donor death circumstances were obtained from a publicly available source. Age distributions for different countries were available online.
JMP 8.0 for Macintosh from SAS was used for curve fitting and statistical analysis. The statistical analysis used least squares analysis and the whole model test.
Both Spain and the United States experienced rapid growth in deceased donor organ donation between the years 1989 and 1999. Although donation rates in both countries grew, the rate in Spain clearly grew more rapidly and increased from 14.3 to 33.6 donors pmp (135%), whereas the rate in the United States increased from 16.2 to 20.9 donors pmp (29%; Fig. 1). The following decade, 1999-2009, saw flattened growth in Spain: the rate increased from 33.6 to 34.4 donors pmp, and this constituted a 2.4% increase in donation over the decade. In contrast, the rate in the United States increased 25.8% from 20.9 to 26.3 donors pmp.
A subanalysis of growth by age groups demonstrated continued discordance in the distribution of donor ages between Spain and the United States. For example, the Spanish age group of 15 to 30 years produced fewer donors in 2009, with the rate dropping from 6.6 to 2.5 donors pmp (−62%), whereas the US donation rate for the age subgroup of 15 to 30 years increased slightly from 5.8 to 6.7 donors pmp (15.5%; Fig. 2B). A more striking discordance in growth was evidenced by the growth in the number of Spanish donors older than 70 years, which increased from 3.8 to 8.8 donors pmp (a 132% increase). In contrast, the rate in the United States increased from only 1.0 to 1.3 donors pmp (Fig. 2F).
The differences in donation rates by age groups have resulted in dramatic differences in the age compositions of the donor pools in Spain and the United States. For example, in 2009, donors who were 60 to 70 years old represented 19.5% of donors in Spain and only 11.4% of donors in the United States. Even more remarkable is the differential percentage of donors older than 70 years, who currently account for 25.4% of Spanish donors and 4.4% of US donors.
Growth in deceased donor utilization was also analyzed by the Organ Procurement and Transplantation Network region for the decades spanning 1990 to 2009. Regional growth in deceased donor donation ranged from −6% (region 6) to 112% (region 2; Fig. 3A). To determine whether regional differences in growth were associated with greater utilization of older donors, the growth percentage (1990-2009) was plotted against the percentage of donors aged 65 or older in 2009 in each UNOS region. In 2009, the percentage of donors older than 65 years ranged from 2.5% to 15.6%. When the percentage growth was plotted against the utilization rate for older donors, a strong and significant association was identified (P < 0.01; Fig. 3B).
Finally, because organs from older donors are placed more often into older recipients, the overall change in the age distributions of donors and recipients was examined for both decades (Fig. 4). For liver transplantation, although growth in donation occurred for all age groups (Fig. 4B), the recipient pool grew disproportionately among the older age groups, with a spike for the age group of 50 to 59 years. A similar pattern occurred in kidney transplantation: there was a rightward shift in the distribution of recipient ages that peaked for the age group of 50 to 59 years (Fig. 4D). When net contributions between donor and recipient distributions were compared, a significant deficit between the utilization of older donor organs and the transplantation of older recipients became apparent.
Although transplantation has undoubtedly lengthened the lifespan and improved the quality of life for thousands of patients, high success rates have encouraged listing for many patients previously thought to be too old or to have excessive medical comorbidities for successful transplantation. Increased access, coupled with limited donor organ availability, has resulted in long wait lists of medically complex patients, many of whom die waiting for an organ. Unfortunately, recipient demand has increased faster than the donor organ supply, and this has exacerbated the shortage.
In response to the worsening shortage, those interested in increasing organ donation have looked for guidance from Spain, which has long been considered the gold standard for organ donation. The phrase Spanish model describes the organizational structure in place to facilitate organ donation in Spain, and it encompasses an entire system starting with presumed-consent legislation followed by efficient methods for donor identification, management, and procurement.[17-19] In 1999, the organ donation rate was 33.6 pmp in Spain versus 21.5 pmp in the United States. A prior analysis of the differences between Spain and the United States3 suggested that a major factor in this difference could be attributed to greater utilization of older donors by Spanish transplant centers rather than structural differences in the organ procurement systems.
From 1999 to 2009, Spanish deceased donor organ donation increased only 2.4% from 33.6 to 34.4 donors pmp. This flattening of Spanish growth occurred despite the increasingly aggressive utilization of donors older than 70 years, who now account for 25.4% of all Spanish deceased donors. Donor age group comparisons of the 2 countries continue to show striking dissimilarities for all donors older than 60 years because these represent just 17.7% of United States donors and 44.9% of Spanish donors.
It is important to recognize that the reported donation rate represents donors from whom at least 1 organ has been procured. This does not reflect the effective donation rate, which represents donors from whom at least 1 organ has been used for transplantation. In Spain, the effective donation rate in 2009 was 29.9 donors pmp, whereas the overall organ donation rate was 34.4 donors pmp (13% of procurements resulted in no organs being transplanted). Furthermore, it is also apparent from the Spanish literature that the percentage of unsuccessful donors is rising because the age of the donor population has risen.[11, 20] Nevertheless, it is clear that the potential resource of older deceased donors is much more effectively used in Spain versus the United States. Increasing donation after cardiac death is another avenue on which both countries have focused in recent years; however, there are no data available to adequately assess the contribution of donors after cardiac death to the overall donation rates and the age distribution. Because of the small number of these donors, it would be expected that their contribution would be small.
Although overcoming structural barriers has benefited the Spanish transplant system, the primary driver for the success of Spanish donation is the greater willingness to use older donors. In fact, Spain may be encountering the natural limits of donation as currently practiced, and it is a concern that the donation rate in the younger age groups has fallen dramatically despite the Spanish model. The decrease in young donors likely reflects positive public health changes in Spanish culture. For example, motor vehicle accidents as a cause of death before donation decreased 72.5% between 2000 (n = 278 or 20.7%) and 2010 (n = 68 or 5.7%). A similar though less pronounced pattern has occurred in the United States: the rate of donors with a motor vehicle accident as the cause of death decreased 34.7% between 2000 (n = 1449 or 24.2%) and 2010 (n = 1255 or 15.8%).
In sum, these growth curves suggest that although Spain is nearing the maximum donor yield under current conditions, the United States continues to have significant unrealized growth potential largely based on increased utilization of older donors. This relationship between older donor utilization rates and growth in donation in the United States is apparent when the growth in donation is analyzed by UNOS regions. Some of the differences seen in the regional utilization patterns of older donors may depend on the perceived need for organs and the degree of competition among centers.[22-24]
An increased acceptance of older donors in the United States closer to the rates of utilization in Spain would help to alleviate the acute shortage of donor organs, shorten waiting times, and potentially allow transplantation earlier in the disease process. Presumably, the primary limiting factor for older donor utilization in the United States is poorer recipient outcomes when older donor organs are transplanted.[25-28] National recipient outcome data for Spain are not available for determining the outcomes of the usage of older donors in that country, but it would be surprising if the outcomes were substantially better than those in the United States. One limitation of this study and similar prior studies comparing differences in donation rates in large populations is the assumption that the donor populations are roughly equal in composition. For example, it may be that an older donor in Spain is generally healthier than a similarly aged donor in the United States; however, multiple confounding variables, such as access to care and rates of obesity, diabetes, and hypertension in the population of older donors, may also be in play. An example might be a differential prevalence of hypertension or obesity between the Spanish and American populations, which would have a downstream effect on the average deceased donor organ quality.[11, 29] Furthermore, differences in the age distributions for the 2 populations (16.5% aged 65+ in Spain versus 12.3% aged 65+ in the United States) may account for a small amount of the variation. Certainly, the issues of differential donor quality and accurate measurements of donors in the elderly deceased donor population warrant further study.
Potential explanations accounting for different donation practices may include center-based result reporting as currently practiced in the United States (which may unduly penalize aggressive centers by insufficiently accounting for the risk of older donors), the cost of the utilization of these organs not being fully reimbursed, the lack of recipient education regarding the potential benefits of using older donors, and concerns about legal liability. In addition to the reluctance of recipient centers to accept these organs for fear of poorer outcomes, older donors may in fact never be reported to procurement organizations because of community perceptions that advanced donor age (>75 years) is a contraindication to donation. Whatever the underlying reason may prove to be, measures addressing the underlying limitations could be the most effective for increasing the overall US deceased donor donation rate to the levels achieved in Spain.