When supply doesn’t meet demand

The continuing shortage of donor organs has rekindled the debate to modify or change Australia’s allocation model. Annie May reports.

Does Australia need a new kidney allocation scheme to address the current shortage of deceased donor kidneys for transplantation? And if so, should that scheme be utility-based?

These are the question that Dr Wai Lim, from Sir Charles Gairdner Hospital’s department of renal medicine, wants people – from healthcare workers to policy makers to the wider community – to ask.

Lim himself does not have a definitive answer to either question, but he is certain a discussion has to happen.

Renal transplantation improves survival of patients with end-stage kidney disease (ESKD), however, Lim says the challenge is the disparity between availability of deceased donor kidneys and potential recipients.

In Australia, the proportion of potential recipients aged 65 years and over awaiting renal transplantation has increased by 21 per cent between 2005 and 2008.

Deceased donor rates in Australia have remained low at 11 donors per million population (pmp) in 2009, compared with 34 pmp in Spain, 24 pmp in the USA and 17 pmp in the UK.

However, there has been an increase in acceptance of older donor kidneys in Australia, with the number of deceased donors aged at 55 years or over increasing from 134 in 2001–2003 to 241 in 2007–2009. This increase saw older donor kidneys representing 34 per cent of overall donations.
While partially offset by the reduction in mortality associated with reduced wait-list time, Lim says kidneys from older donors are associated with inferior graft outcomes including late graft loss, chronic allograft nephropathy and higher risk of cardiovascular mortality.

“Donor kidneys are a scare resource, and unless the number of donors increases they will continue to become more scarce,” Lim told Nursing Review.

“Given this, there is concern surrounding the allocation of donor kidneys, especially younger donor kidneys, to elderly potential recipients. Many older recipients will die with functioning grafts, a proportion of which may have continued to function for a considerable period in younger recipients.
“As older recipients have shorter life expectancies, adopting an allocation strategy that better matches the life expectancy of the donor kidney with that of the recipient may be appropriate.”

Allocation strategies include the concept of donor–recipient age-matching and the creation of a kidney allocation score (KAS) to improve the utility of deceased donor kidneys.

Allocation of deceased donor kidneys according to donor–recipient age-matching avoids the allocation of younger donor kidneys to older recipients and older donor kidneys to younger recipients according to a single donor and recipient age cut-off value.

A KAS is determined from the following components: life years from transplant (LYFT, which is the estimated survival a recipient of a specific donor kidney may expect to receive compared to remaining on dialysis); dialysis time (DT, time spent on dialysis allows candidates to gain priority based upon the length of time they have been receiving this treatment); and Donor Profile Index (DPI, which measures donor quality).

In Australia, the initial allocation of deceased donor kidneys occurs at a national level, involving all potential recipients on the wait list. Around 20 per cent of available deceased donor kidneys are allocated according to the Interstate Exchange Program, where the kidneys are shipped to potential recipients who are highly sensitized and with zero to two HLA-mismatches.

However, the majority of the deceased donor kidneys are allocated locally according to primarily HLA-matching and time on dialysis. Although older donor kidneys are associated with shorter graft survival and poorer post-transplant graft function, donor issues such as age are not explicitly considered in the allocation algorithm, says Lim.

“Some age matching still occurs, because a younger healthier potential recipient near the top of the list may decline a marginal kidney, and retain their place on the waiting list until a younger kidney becomes available.”

In an article published in Nephrology, Lim and fellow authors said it remained unclear whether the implementation of utility-based allocation models would achieve a better balance between utility and equity.

“While kidney transplantation is more cost effective than dialysis, it will take considerable time for the expected lower long-term cost to offset the high initial cost associated with transplantation. In older recipients who are more likely to die with a functioning graft, the expense of transplantation may not be justified, on an economic basis, especially with a high-quality donor kidney.”

Although age-matching allocation is simple to implement, Lim says chronological age can be a poor measure of physiological age. As a result, allocation policy based solely on age-matching could disadvantage a number of healthy older potential recipients.

“As age is not the sole determinant of allocation, KAS may be a more equitable means to allocate deceased donor kidneys. However, this will be difficult to implement in clinical practice. Reliance of LYFT may disadvantage certain ‘high-risk’ groups, such as indigenous, who will have a higher predicted graft loss, resulting in a lower LYFT.

“Although a combination of LYFT with factors such as dialysis time and donor quality has been suggested, the optimum weighting of these or other factors in the allocation model remains uncertain.

However, whether LYFT will achieve a better balance between utility and equity compared with age-matching remains debatable. In order to consider using KAS in kidney allocations in Australia, LYFT will need to be derived and validated using a combination of historical datasets from ANZDATA and local transplanting centres.

“Compared with Australia’s current allocation policy, the authors state that alternative utility-based allocation models (age-matching or KAS) will “no doubt lead to an improvement in transplant graft life.” But this maybe at the expense of transplant equity as older potential recipients are less likely to be offered younger donor kidneys.”

Compared with KAS, age-matching is an easier model to implement and if this is integrated with the country’s current allocation model, which takes into account the degree of sensitisation, HLA-matching and time on dialysis. Lim says it may achieve a better balance between transplant utility and equity compared with either model alone. In Australia, the number of older potential recipients far exceeds that of older donors.

In 2008, there were 123 older potential recipients (aged 65 years and over) on the wait list compared with the availability of only 60 older donor kidneys (aged 65 years and over).

Although there is a large discrepancy between the number of available donor kidneys and wait-listed potential recipients across all donor and recipient age groups, there is a lesser difference at the extremes of donor and recipient age under 35 and over 65 years.

“One potential option of assimilating age-matching into the current allocation model may be to consider age-matching at the younger age group, for example all donor kidneys aged under 35 years must be allocated to potential recipients aged under 35 years, while acknowledging that a proportion of younger recipients will continue to receive older donor kidneys.”

Lim is clear in stating he is unsure what model would be best, however he says the conversation needs to start.

“Optimising the use of our limited pool of deceased donor kidneys needs to be considered a priority.

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