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A new allocation plan for renal transplantation
A New Allocation Plan for Renal Transplantation F.L. Delmonico, W.E. Harmon, M.I. Lorber, J. Goguen, H. Mah, J. Himmelfarb, G. Lipkowitz, S. Valliere, L. Bow, E.L. Milford, and R.J. Rohrer
T
HE New England Region is a microcosm of the Organ Procurement and Transplantation Network (OPTN), with differing ethnic cultures and degrees of urbanization, and a large number of transplant programs and patients served. Since September 1996, an experimental method of kidney allocation, devised with the approval of UNOS and its Region 1 transplant centers, has been used for the distribution of renal allografts. The 16 transplant centers of UNOS Region 1 are located in all six New England states, and they are represented by two organ procurement organizations (OPOs), the New England Organ Bank (NEOB: 14 centers) and the Northeast Organ Procurement Organization (NEOPO: 2 centers). A UNOS Region 1 trial of renal allocation was conducted in two time periods: between September 3, 1996, and September 2, 1997; and after subsequent alterations were made in the plan, from December 1, 1997, to March 1998. There was a 3-month hiatus of data collection (September to December 1997) as Region centers and UNOS considered modifications to the plan, implemented in December 1997. The objective of the plan was to allocate cadaver donor renal allografts throughout the entire Region by a single list, based upon HLA matching, time waiting, and population distance points. The experimental plan was designed to provide a balance between increasing the opportunity for those patients listed with long waiting times and promoting local donor availability.
METHODS Each list of Regional candidates was formulated by assigning a maximum of 8 points for time waiting, a maximum of 8 points for population distance between the donor hospital and the potential recipient hospital, and HLA match points (7, 5, 2, or 0 as per the standard UNOS algorithm) based upon of the degree of B/DR mismatch. Time waiting points were defined by the following exponential formula:
@x^2/9# 1 @y 2 8^2/64# 5 1, where x 5 waiting time in years with a maximum of 3 years; and y 5 waiting points with a maximum of 8 points. The curve used in the calculation was the right lower quadrant of an ellipse. Waiting time did not commence until the candidate had begun dialysis. Transplant candidates who were on the list as of March 4, 1996 (the date Region 1 voted to approve the experimental plan) and who were not on dialysis were able to retain waiting time accumulated prior to that date. Thereafter, candidates who were previously on 0041-1345/99/$–see front matter PII S0041-1345(98)01660-1
the list, or candidates who were subsequently placed on the list, would not receive waiting-time points unless they had initiated dialysis. To establish population distance as the other principal basis for equitable distribution of renal allografts, the population within the distance from each donor site to each recipient site (initially using transplant center zip codes from tables in the UNOS database) was calculated. For recipient candidates at a given transplant center, the distance from the donor hospital was the radius of a circle. When zip codes were later found to be an unreliable measure of distance, populations within the circle of the given radius were computed by UNOS using a house-by-house program called Atlas GIS, Strategic Mapping, Inc. (James Strawn, UNOS). Population data was obtained from the 1990 United States census. The total population within this circle from the donor site to the recipient centers was the basis for population distance points (popdp) awarded to all patients at that transplant center. If the population within the circle from the donor site to the transplant center exceeded 5 million, the popdp was 0. The curve used in the calculation of popdp was the left lower quadrant of an ellipse, ranging from a maximum of 8 points for a very small population distance radius, to 0 points for 5 million or more population within the circle, computed for each donor. An additional 4 points were awarded to a T-cell crossmatchnegative patient with a panel reactive antibody (PRA) level of $80%, and to pediatric patients. Thus, the total number of points that could conceivably be accumulated with each donor was 27 for an adult-sensitized recipient and 31 for a pediatric-sensitized recipient. The candidate with the highest point total was offered the first available kidney from a Region 1 donor. If two patients had the same point accumulation to the fourth decimal place, the kidney was awarded to the patient with the longest waiting time.
RESULTS
During the first 12 months of the trial, there were 181 organ donors and 362 renal allografts recovered, respectively. Sixty-one percent (220) were allocated by the Region 1 plan. The total number of kidneys imported and exported by UNOS mandatory share was 72 and 68, respectively.
From the UNOS Region 1 Renal Data Committee. Address reprint requests to Francis L. Delmonico, MD, Medical Director, New England Organ Bank, One Gateway Center, Newton, MA 02458-2803. © 1999 by Elsevier Science Inc. 655 Avenue of the Americas, New York, NY 10010
358
Transplantation Proceedings, 31, 358–359 (1999)
A NEW RENAL ALLOCATION PLAN
359
Allocation by Waiting Time and Population Distance Points
Revised Allocation by HLA Points
The total number of kidneys transplanted to patients with .3 years time waiting was 100 (46%) and .2.5 to 3 years waiting was 29 (13%). However, the total number of kidneys transplanted to patients with the maximum population distance points was only 72 (33%). Thus, although the plan achieved a favorable distribution of kidneys to patients with longer waiting times (nearly 60%), the other equally important objective of promoting local donor availability (only 33% of the allocated kidneys with maximum popdp) was not as effectively accomplished (also see HLA data below, which had an unanticipated impact upon the relative weight of popdp). Furthermore, the percentage of kidneys exported by the UNOS mandatory share far exceeded the anticipated number as the plan was conceived (nearly 20%).
Only 1 patient received 7 HLA points, and with the deletion of the other B/DR MM considerations, no other HLA points were awarded.
Allocation by HLA Points
The total number of patients who received an allograft with 5 or 2 HLA points (1 or 2 B/DR MM) was 119 (55%). Only 3 patients received 7 HLA points. Thus, minor B/DR differences were unexpectedly consequential to allocation, and they represented a change in the approach from the Region’s previous system of allocation. METHOD REVISIONS
Following review of the first year data (between September 3, 1996, and September 2, 1997), initially by the Region 1 Renal Data Committee and subsequently by representatives of all Region 1 transplant centers, the UNOS Board approved the following recommended adjustments in the plan as of December 1, 1997: a maximum of 10 popdp by a linear formula: a maximum of 8 points for time waiting by linear correlation; and the retention of only 7 HLA points for 0 B/DR MM (2- and 5-point categories deleted). REVISION RESULTS
During the first 3 months of the revised plan, the number of kidney organ donors and renal allografts recovered were 64 and 109, respectively. The percentage of kidneys allocated by the plan was 71.6% (total 78), an increase of 10% from the first-year plan. The percentage of kidneys exported by UNOS mandatory share (0 mismatch phenotypic or payback) fell from 20% to 16.5%. Allocation by Waiting Time and Population Distance Points
The total number of kidneys transplanted to patients with .3 years time waiting was 25 (32%) and .2.5 to 3 years waiting 22 (28%). Thus, the percentage of patients with long waiting time receiving a kidney was similar to that of the first-year plan (59% vs 60%). Moreover, the percentage of kidneys transplanted to patients with the maximum popdp was also similar (33% vs 35%). However, the percentage of patients receiving a kidney with no popdp fell substantially, from 15% to 4%.
DISCUSSION
The objectives of this allocation strategy were to achieve a sharing of kidneys across an entire Region, while addressing a balance between transplantation for those listed with long waiting times and promoting local organ donor availability. Progress toward these goals was accomplished. Approximately 60% of the renal allografts have been allocated to Region 1 recipients with long waiting times (.2.5 years) by both the initial and the revised experimental plan. Meanwhile, the revision intended to enhance local donor availability by increasing popdp to 10 points by a linear correlation also increased the allocation of kidneys to patients within the circle of 5 million population density. Only 4% of renal allografts allocated by the revised plan (vs 15% in the initial trial) were given to patients with 0 popdp. New England urban programs have suggested that promoting local donor availability enhances organ donation efforts within their area. Although this perspective might be difficult to substantiate by a compilation of scientific data, the alternative of emphasizing equity by time waiting as the only component of allocation could otherwise result in the following: (1) threaten the existence of renal transplant centers in rural areas; (2) create an inequity for patients by forcing them to travel long distances for a standard treatment that should be available in their locale; (3) promote a misperception regarding fairness that might provoke patients and their centers to seek allocation solutions through state legislation; and (4) precipitate the formation of additional OPOs within a Region for the sole purpose of achieving an allocation advantage. All of these alternative scenarios were obviated by the Region 1 plan. The mean preservation time was reduced from approximately 18 to 16 hours when comparing the preservation times prior to and following the implementation of the Region 1 plan. Importantly, the rates of immediate and delayed graft function following transplantation were unchanged. Another end point was to determine whether the disparity in wait times between centers with large lists (.100 candidates) and those with smaller lists (,50 candidates) would be brought together. Although the wait time increased for all centers as the shortage of cadaver donor renal allografts persisted, the extreme differences prevalent in wait times between state locales before the plan were reduced. CONCLUSION
Finally, we have described our initial experience and successful evolution of a formula-based system for organ allocation, which balances legitimate competing priorities. This novel plan, conceived within the transplant community itself, suggests that a heterogeneous region of multiple transplant centers can implement a plan of allocation that successfully provides for an ever-increasing number of patients.
T
HE New England Region is a microcosm of the Organ Procurement and Transplantation Network (OPTN), with differing ethnic cultures and degrees of urbanization, and a large number of transplant programs and patients served. Since September 1996, an experimental method of kidney allocation, devised with the approval of UNOS and its Region 1 transplant centers, has been used for the distribution of renal allografts. The 16 transplant centers of UNOS Region 1 are located in all six New England states, and they are represented by two organ procurement organizations (OPOs), the New England Organ Bank (NEOB: 14 centers) and the Northeast Organ Procurement Organization (NEOPO: 2 centers). A UNOS Region 1 trial of renal allocation was conducted in two time periods: between September 3, 1996, and September 2, 1997; and after subsequent alterations were made in the plan, from December 1, 1997, to March 1998. There was a 3-month hiatus of data collection (September to December 1997) as Region centers and UNOS considered modifications to the plan, implemented in December 1997. The objective of the plan was to allocate cadaver donor renal allografts throughout the entire Region by a single list, based upon HLA matching, time waiting, and population distance points. The experimental plan was designed to provide a balance between increasing the opportunity for those patients listed with long waiting times and promoting local donor availability.
METHODS Each list of Regional candidates was formulated by assigning a maximum of 8 points for time waiting, a maximum of 8 points for population distance between the donor hospital and the potential recipient hospital, and HLA match points (7, 5, 2, or 0 as per the standard UNOS algorithm) based upon of the degree of B/DR mismatch. Time waiting points were defined by the following exponential formula:
@x^2/9# 1 @y 2 8^2/64# 5 1, where x 5 waiting time in years with a maximum of 3 years; and y 5 waiting points with a maximum of 8 points. The curve used in the calculation was the right lower quadrant of an ellipse. Waiting time did not commence until the candidate had begun dialysis. Transplant candidates who were on the list as of March 4, 1996 (the date Region 1 voted to approve the experimental plan) and who were not on dialysis were able to retain waiting time accumulated prior to that date. Thereafter, candidates who were previously on 0041-1345/99/$–see front matter PII S0041-1345(98)01660-1
the list, or candidates who were subsequently placed on the list, would not receive waiting-time points unless they had initiated dialysis. To establish population distance as the other principal basis for equitable distribution of renal allografts, the population within the distance from each donor site to each recipient site (initially using transplant center zip codes from tables in the UNOS database) was calculated. For recipient candidates at a given transplant center, the distance from the donor hospital was the radius of a circle. When zip codes were later found to be an unreliable measure of distance, populations within the circle of the given radius were computed by UNOS using a house-by-house program called Atlas GIS, Strategic Mapping, Inc. (James Strawn, UNOS). Population data was obtained from the 1990 United States census. The total population within this circle from the donor site to the recipient centers was the basis for population distance points (popdp) awarded to all patients at that transplant center. If the population within the circle from the donor site to the transplant center exceeded 5 million, the popdp was 0. The curve used in the calculation of popdp was the left lower quadrant of an ellipse, ranging from a maximum of 8 points for a very small population distance radius, to 0 points for 5 million or more population within the circle, computed for each donor. An additional 4 points were awarded to a T-cell crossmatchnegative patient with a panel reactive antibody (PRA) level of $80%, and to pediatric patients. Thus, the total number of points that could conceivably be accumulated with each donor was 27 for an adult-sensitized recipient and 31 for a pediatric-sensitized recipient. The candidate with the highest point total was offered the first available kidney from a Region 1 donor. If two patients had the same point accumulation to the fourth decimal place, the kidney was awarded to the patient with the longest waiting time.
RESULTS
During the first 12 months of the trial, there were 181 organ donors and 362 renal allografts recovered, respectively. Sixty-one percent (220) were allocated by the Region 1 plan. The total number of kidneys imported and exported by UNOS mandatory share was 72 and 68, respectively.
From the UNOS Region 1 Renal Data Committee. Address reprint requests to Francis L. Delmonico, MD, Medical Director, New England Organ Bank, One Gateway Center, Newton, MA 02458-2803. © 1999 by Elsevier Science Inc. 655 Avenue of the Americas, New York, NY 10010
358
Transplantation Proceedings, 31, 358–359 (1999)
A NEW RENAL ALLOCATION PLAN
359
Allocation by Waiting Time and Population Distance Points
Revised Allocation by HLA Points
The total number of kidneys transplanted to patients with .3 years time waiting was 100 (46%) and .2.5 to 3 years waiting was 29 (13%). However, the total number of kidneys transplanted to patients with the maximum population distance points was only 72 (33%). Thus, although the plan achieved a favorable distribution of kidneys to patients with longer waiting times (nearly 60%), the other equally important objective of promoting local donor availability (only 33% of the allocated kidneys with maximum popdp) was not as effectively accomplished (also see HLA data below, which had an unanticipated impact upon the relative weight of popdp). Furthermore, the percentage of kidneys exported by the UNOS mandatory share far exceeded the anticipated number as the plan was conceived (nearly 20%).
Only 1 patient received 7 HLA points, and with the deletion of the other B/DR MM considerations, no other HLA points were awarded.
Allocation by HLA Points
The total number of patients who received an allograft with 5 or 2 HLA points (1 or 2 B/DR MM) was 119 (55%). Only 3 patients received 7 HLA points. Thus, minor B/DR differences were unexpectedly consequential to allocation, and they represented a change in the approach from the Region’s previous system of allocation. METHOD REVISIONS
Following review of the first year data (between September 3, 1996, and September 2, 1997), initially by the Region 1 Renal Data Committee and subsequently by representatives of all Region 1 transplant centers, the UNOS Board approved the following recommended adjustments in the plan as of December 1, 1997: a maximum of 10 popdp by a linear formula: a maximum of 8 points for time waiting by linear correlation; and the retention of only 7 HLA points for 0 B/DR MM (2- and 5-point categories deleted). REVISION RESULTS
During the first 3 months of the revised plan, the number of kidney organ donors and renal allografts recovered were 64 and 109, respectively. The percentage of kidneys allocated by the plan was 71.6% (total 78), an increase of 10% from the first-year plan. The percentage of kidneys exported by UNOS mandatory share (0 mismatch phenotypic or payback) fell from 20% to 16.5%. Allocation by Waiting Time and Population Distance Points
The total number of kidneys transplanted to patients with .3 years time waiting was 25 (32%) and .2.5 to 3 years waiting 22 (28%). Thus, the percentage of patients with long waiting time receiving a kidney was similar to that of the first-year plan (59% vs 60%). Moreover, the percentage of kidneys transplanted to patients with the maximum popdp was also similar (33% vs 35%). However, the percentage of patients receiving a kidney with no popdp fell substantially, from 15% to 4%.
DISCUSSION
The objectives of this allocation strategy were to achieve a sharing of kidneys across an entire Region, while addressing a balance between transplantation for those listed with long waiting times and promoting local organ donor availability. Progress toward these goals was accomplished. Approximately 60% of the renal allografts have been allocated to Region 1 recipients with long waiting times (.2.5 years) by both the initial and the revised experimental plan. Meanwhile, the revision intended to enhance local donor availability by increasing popdp to 10 points by a linear correlation also increased the allocation of kidneys to patients within the circle of 5 million population density. Only 4% of renal allografts allocated by the revised plan (vs 15% in the initial trial) were given to patients with 0 popdp. New England urban programs have suggested that promoting local donor availability enhances organ donation efforts within their area. Although this perspective might be difficult to substantiate by a compilation of scientific data, the alternative of emphasizing equity by time waiting as the only component of allocation could otherwise result in the following: (1) threaten the existence of renal transplant centers in rural areas; (2) create an inequity for patients by forcing them to travel long distances for a standard treatment that should be available in their locale; (3) promote a misperception regarding fairness that might provoke patients and their centers to seek allocation solutions through state legislation; and (4) precipitate the formation of additional OPOs within a Region for the sole purpose of achieving an allocation advantage. All of these alternative scenarios were obviated by the Region 1 plan. The mean preservation time was reduced from approximately 18 to 16 hours when comparing the preservation times prior to and following the implementation of the Region 1 plan. Importantly, the rates of immediate and delayed graft function following transplantation were unchanged. Another end point was to determine whether the disparity in wait times between centers with large lists (.100 candidates) and those with smaller lists (,50 candidates) would be brought together. Although the wait time increased for all centers as the shortage of cadaver donor renal allografts persisted, the extreme differences prevalent in wait times between state locales before the plan were reduced. CONCLUSION
Finally, we have described our initial experience and successful evolution of a formula-based system for organ allocation, which balances legitimate competing priorities. This novel plan, conceived within the transplant community itself, suggests that a heterogeneous region of multiple transplant centers can implement a plan of allocation that successfully provides for an ever-increasing number of patients.