key: cord-0954541-jfao5rv1
authors: Cooper, Matthew; Leeser, David B.; Flechner, Stuart M.; Beaumont, Jennifer L.; Waterman, Amy D.; Shannon, Patrick W.; Ronin, Matthew; Hil, Garet; Veale, Jeffrey L.
title: Ensuring the need is met: A 50‐year simulation study of the National Kidney Registry’s family voucher program
date: 2020-06-25
journal: Am J Transplant
DOI: 10.1111/ajt.16101
sha: c33a49b8f1e208bb0b89f638d382f0f6c31634a7
doc_id: 954541
cord_uid: jfao5rv1

The National Kidney Registry (NKR) Advanced Donation Program enables living donors the opportunity to donate altruistically, or in advance of a potential recipient's transplant, and to receive a voucher that can be redeemed for a future transplant facilitated by the NKR. Family vouchers allow a donor to identify multiple individuals within their immediate family, with the first person in that group in need of a transplant being prioritized to receive a kidney. An increase in vouchers introduces concerns that demand for future voucher redemptions could exceed the supply of available donors and kidneys. A Monte Carlo simulation model was constructed to estimate the annual number of voucher redemptions relative to the number of kidneys available over a 50‐year time horizon under several projected scenarios for growth of the program. In all simulated scenarios, the number of available kidneys exceeded voucher redemptions every year. While not able to account for all real‐life scenarios, this simulation study found that the NKR should be able to satisfy the likely redemption of increasing numbers of vouchers under a range of possible scenarios over a 50‐year time horizon. This modeling exercise suggests that a donor family's future needs can be satisfied through the voucher program.

of advancements allowing for greater separation of time between donor and recipient surgeries for pairs who are chronologically incompatible. 3 The NKR developed the Advanced Donation Program (ADP) to support KPDs in these increasingly complex scenarios (see Table 1 for definitions). 4 When a patient donates to a recipient before their intended recipient receives a kidney, a voucher is issued, enabling their intended recipient to redeem the voucher and receive a KPD transplant if needed. In the original implementation of the program, the voucher is issued to a single, intended recipient, with known history of disease and an expected future transplant need, and can be redeemed if, and when, a kidney transplant is necessary. Voucher program is expected to increase LDKT while providing additional security to donors and their family members with no increased risk of renal disease. While exciting, this innovation will likely increase the number of vouchers outstanding, raising concerns that demand for future voucher redemptions could exceed the supply of available kidneys to meet that demand. Thus, the goal of this effort is to address this redemption concern through a Monte Carlo simulation model.

A Monte Carlo simulation model 5 was constructed to estimate the annual number of voucher redemptions relative to the number of kidneys available for transplant over a 50-year time horizon under several projected scenarios. Monte Carlo computer simulation models are commonly used in a wide range of fields such as finance, insurance, and transportation to perform risk analyses in complex situations where it is not possible to mathematically calculate future values for important outcome variables and have been applied in projecting availability of donor livers 6 and impact of organ allocation strategies. [7] [8] [9] Our model tracks simulated donors and voucher holders until either a voucher is redeemed, the voucher holder dies, or the voucher "expires" (voucher holder reaches age 85 or another voucher holder from the same family redeems voucher). The flow of the model is depicted in Figure 1 . The simulation model was programmed and run using ASP.NET 4.5.2.

The circle in Figure 1 

Using the base input values discussed above, the simulation model 

Ages of new voucher holders generated each year were randomly 

The simulation model developed for this study is capable of analyz- 

Under this scenario, voucher donors increased at an average rate of 5% per year over the 50 years. Thus, both the NKR liability to meet potential voucher redemptions and the available donor supply are assumed to increase rapidly. Figure 2A illustrates 

In this scenario, the rate of growth in voucher donors increased between 2 and 5 per year, a much lower rate than scenario 1. In this case, the voucher liability increases slowly but so does donor availability. Figure 3A illustrates the 10th percentile coverage ratios by

year. As in scenario 1, there is virtually no risk of insufficient donors to meet the required voucher redemptions. Year 40 exhibits the lowest coverage ratio at 3.71. Figure 3B 

This scenario is considered a worst case since it has voucher liability growing rapidly during the first 25 years followed by rapid decline the next 25 years. This builds significant potential liability early followed by reduced donor availability later when the chances of voucher redemption would be predicted to increase. Figure 4A Thus, the late donor shortage risk associated with this scenario, while higher than for scenarios 1 and 2, is still very low. Figure 6B illustrates that at the 10th percentile level, the number of donors in

year 50 (210) exceeds the number of redemptions (73).

The ongoing kidney donor shortage continues to fuel creative strategies to increase LDKT rates and seek additional protections for living donors. KPD arose as a successful innovation to address incompatibility. Vouchers now address "chronological incompatibility" when the donor wishes to donate years prior to their intended recipient's transplantation. Initially, vouchers were given to individuals with kidney dysfunction in imminent need of transplant, but currently the program includes voucher holders without kidney dysfunction. While the program is promising, the concern regarding insufficient allografts to accommodate these vouchers must be addressed. This simulation study has demonstrated that the expanded voucher program should satisfy the likely redemption of vouchers under a range of possible scenarios over a 50year time horizon. In addition, these improvements to the voucher F I G U R E 4 A, In the rapid growth followed by rapid decline scenario, coverage ratios at the first, fifth, 10th, and 50th percentiles are illustrated (1000 simulations). The coverage ratio is the number of available donors per voucher redemption. A coverage ratio of 2.0 indicates there are twice as many donor kidneys available as there are voucher redemptions in that year. B, In the rapid growth followed by rapid decline scenario, total available donors and voucher redemptions along with the coverage ratio at the 10th percentiles are illustrated (1000 simulations)

program will provide needed protections for potentially more KPD donors.

Ensuring confidence among the transplant community and the general public that kidney donors will be available in the future to meet all requests for voucher redemption is essential. Similar to a bank's capital requirements when a customer wishes to make a with- 

The data that support the findings of this study are available from the corresponding author upon reasonable request.

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