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Kidney and Pancreas Distribution Modeling: Analysis at a Glance

The goals of removing donation service area (DSA) and region from kidney and pancreas distribution are to create more equity in access to transplantation for candidates regardless of where they live, and to ensure that these allocation policies meet the requirements of the OPTN Final Rule. Under current allocation, research performed by the OPTN highlights the candidates’ place of residence or listing as the largest factor related to disparity in kidney allocation1.

The OPTN Kidney and Pancreas Transplantation Committees both have worked to identify alternatives to DSA and region that improve overall equity in geographic distribution. This effort does not affect  other important allocation factors, such as keeping the elevated priority for highly sensitized patients. The goal of this project is to revise the role of geography for kidney, pancreas and combined kidney-pancreas transplants.  Work related to multi-organ priority is out of scope and will be addressed in a future, cross-organ policy project.

Alongside committee clinical and professional experience, the SRTR Kidney-Pancreas Simulation Allocation Model (KPSAM) is an important tool that OPTN committees use when developing changes to organ allocation policy.  The latest SRTR report models proposed replacements of current DSA and region boundaries in kidney and pancreas allocation with single-circle allocation systems of 150, 250, or 500 nautical miles (read about the different modeling input on page 3 of the full report).  Any organs not accepted inside the first circle of allocation would be offered at the national level.

Below are some takeaways from the latest modeling:

  • Nearly all scenarios yielded similar results in terms of effects on subpopulations.
  • Kidney transplant rates remained nearly constant under broader distribution:

o   Rates among pediatric, female, African American, and Latino candidates increased.

o   Rates among highly sensitized (80-99% cPRA) and high dialysis time (> 5 years) candidates increased.

  • Slight decreases were noted in transplant rates for non-metropolitan candidates and no change in percentage of kidney alone transplants. Modeling indicates that candidates in rural areas would have similar rates of transplant compared to candidates in cities.
  • The larger the circle is, the farther distance organs would travel.  This may lead to increased cost and logistic issues for which there is only anecdotal evidence to examine.
  • Kidney-pancreas transplant rates increased across all broader distribution scenarios modeled:

o   In general, the kidney-pancreas transplant rate increased as the circle size increased.

o   Percentages of transplants among African American, and females increased.

o   Rates among highly sensitized (80-98% cPRA) candidates increased.

o   As the pancreas circle size increases, KP transplant counts increased, leading to subsequent decreases in kidney and pancreas alone transplants. This is due to the absolute priority KP candidates are given over kidney and pancreas alone candidates at the current local level.

  • Although the model predicts that pancreas alone transplant rates decrease across each scenario, the Committee notes that the model does not reflect individual program behavior.

Overall:

  • While there was a projected decrease in kidney alone and pancreas alone transplants, when examining the total number of kidney transplants (kidney alone and KP), the total number of transplants varied little across model variations, and almost no change was seen from baseline.
  • As expected, the decrease in kidney alone, and simultaneous increase in kidney-pancreas, saw the largest change in the biggest circles (e.g. 500 NM) and change was minimized in the smaller circles (e.g. 150 NM).
  • Proximity points are considered being added to current candidate characteristics that currently receive points, such as candidate CPRA or ABDR-mismatching in kidney allocation, to weight proximity to the donor in matching potential transplant recipients to deceased donor organs. Higher values of proximity points would indicate that a larger weight, or value, is placed on geography; candidates closer to the donor in proximity would receive more proximity points than candidates further away. It’s also important to note that candidates cannot move from outside the circle to inside the circle, regardless of how many proximity points are assigned.  The function of proximity points is addressed in a prior concept paper.
  • KPSAM results showed that proximity points were successful in reducing travel of the organ inside the circle, but were less impactful in national allocation. However, a relatively small number of organs (10-20 percent) are predicted to occur nationally, which may be an under prediction. Given the limitations of the KPSAM, there is likely a larger number of transplants occurring from acceptances further down the match than sequence #200 that aren’t accounted for in the results due to computational and other modeling limitations.

It is important to note that modeling cannot account for changes in organ acceptance behavior or identify trends over time, and that the output would not reflect instances of transplants for organs accepted past 200 in the sequence of offers.

If you have any questions about the next steps for changing these policies or about the modeling, please contact Scott Castro (scott.castro@unos.org) or Amber Wilk (amber.wilk@unos.org) for kidney questions and Abby Fox (abigail.fox@unos.org) or Read Urban (read.urban@unos.org) for pancreas questions.

Defined Terms

cPRA = calculated panel reactive antibodies

EPTS = estimated post-transplant survival

KPSAM = Kidney-Pancreas Simulation Allocation Model

NM = nautical miles

OPTN = Organ Procurement and Transplantation Network

SRTR = Scientific Registry of Transplant Recipients

 

1Stewart DE, Wilk AR, Toll AE, et al. Measuring and monitoring equity in access to deceased

donor kidney transplantation. Am J Transplant. 2018;00:1–12. https://doi.org/10.1111/ajt.14922.