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UNOS Researchers Present Studies at American Transplant Congress

UNOS staff members authored and will present several studies at the American Transplant Congress (ATC), held May 2-6 at the Pennsylvania Convention Center. UNOS staff members are primary authors of a total of 15 abstracts and are coauthors of an additional six abstracts.

NOTE: Some of these studies were supported wholly or in part by Health Resources and Services Administration contract 234-2005-37011C. The content is the responsibility of the authors alone and does not necessarily reflect the views or policies of the Department of Health and Human Services, nor does mention of trade names, commercial products, or organizations imply endorsement by the U.S. Government.

Below is a listing of studies in which UNOS researchers are primary authors. UNOS staff researchers are indicated with an asterisk.

Relationship of Donor Age and Distance in Deceased Donor Lung Offers in the United States
Embargo until Saturday, May 2 – 5:30 p.m. EDT
Authors: Leah Edwards, Ph.D.*, Liz Robbins Callahan, Esq.*, Wida Cherikh, Ph.D.*, Joseph Rogers, M.D., Kevin Chan, M.D.

Utilization of lungs from deceased donors is considerably lower than utilization of organs such as kidney, liver and heart. The researchers studied utilization of deceased donor lungs recovered between 2009 and 2013, based on donor age and geographic distance between donor and recipient, to identify patterns of organ offers and transplants and identify potential areas for process improvement.

Donors between the ages of 15 and 44 were most likely to have lungs offered for transplant and to result in at least one lung transplanted. As donor age increased beyond 45, progressively fewer transplant offers were made and fewer transplants occurred.

While many lungs were offered to programs beyond a 500-mile radius of the donor location, only seven percent of lungs were transplanted beyond 500 miles. Lungs from infant donors, as well as those from donors age 70 or older, were more likely to be transplanted at more distant programs than lungs from donors of other age groups.

Predictors of Deceased Donor Lung Utilization in the United States
Embargo until Saturday, May 2 – 5:30 p.m. EDT
Authors: Leah Edwards, Ph.D.*, Liz Robbins Callahan, Esq.*, Joseph Rogers, M.D., Kevin Chan, M.D.

Various clinical factors affect the likelihood of acceptance of donor lungs. The researchers developed six classification groups based on lung donor characteristics and compared them to utilization of deceased donor lungs recovered between 2009 and 2013.

The six classification groups resulted in a wide range of utilization rates, from as low as 1.9 percent to as high as 72.8 percent. While the combination of specific factors within the classification groups is important, the groups with highest utilization tended to include brain-death donors and donors of younger age. Two clinical factors (arterial oxygen pressure, and the ratio of arterial oxygen pressure to the fraction of inspired oxygen in the blood) may be modifiable through clinical management of the potential donor, increasing the potential for lung utilization.

Can Post-Transplant C-Peptide Be Used as an Indicator of Pancreas Graft Failure?
Embargo until Sunday, May 3 – 2:15 p.m. EDT
Authors: Robert Carrico, Ph.D.*, Jonathan Fridell, M.D., Jon Odorico, M.D., Robert Stratta, M.D., Kristina Tyler, J.D.*, Silke Niederhaus, M.D., Raja Kandaswamy, M.D., Jonathan Fisher, M.D., Oyedolamu Olaitan, M.D., Muhammad Mujtaba, M.D.

The OPTN/UNOS Pancreas Transplantation Committee is studying clinical measures and endpoints to define the failure of a transplanted pancreas. One suggested measure is a transplant recipient’s post-transplant C-peptide values (a measure of how much insulin a person’s pancreas is producing). The researchers analyzed voluntarily submitted data regarding reported graft failures from seven transplant centers to assess the value of this measure.

Based on the results analyzed, C-peptide is not supported as a primary factor in the definition of graft failure. Currently, transplant centers either declare graft failure at various levels of C-peptide or do not consistently collect and apply the data as a measure of graft function.

Is Transplant Volume Associated with Survival in Pediatric Liver Transplants?
Embargo until Sunday, May 3 – 2:39 p.m. EDT
Authors: Wida S. Cherikh, Ph.D.*, H.B. Kim, M.D., Amber Wilk, Ph.D.*, Christine Flavin, M.P.H.*, Eileen Brewer, M.D.

Center-specific volume (the number of transplants performed at an individual transplant center) has been shown to correlate with outcomes for many procedures in the adult population. The researchers studied the association between transplant volume and survival for liver transplants performed over a 10-year period for recipients younger than age 18. The OPTN/UNOS Pediatric Transplantation Committee has recommended 18 as a minimal transplant volume that demonstrates pediatric liver training and expertise.

During the study period, 97 percent of the liver transplants were performed at 55 “high-volume” programs, defined as a program that performed at least 18 transplants for patients younger than age 18. An additional 42 programs that were categorized as “low-volume” performed 3 percent of the liver transplants for patients younger than 18.

The high-volume programs were associated with statistically significant higher outcomes five years after the transplant, both in graft and patient survival. This finding supports further investigation of minimal experience criteria for physicians and surgeons caring for pediatric liver recipients.

Why are Pancreas Transplant Volumes Declining?
Embargo until Sunday, May 3 – 2:15 p.m. EDT
Authors: Robert Carrico, Ph.D.*, Jonathan Fridell, M.D., Jon Odorico, M.D., Heidi Yeh, M.D., Kristina Tyler, J.D.*, Silke Niederhaus, M.D.

The number of pancreas transplants performed in the United States has declined since the mid-2000s. The researchers analyzed characteristics of waitlisted pancreas candidates, deceased pancreas donors, and pancreas and kidney recipients to assess what may account for the trend.

Despite conjecture that more pancreata are being discarded after recovery for transplantation, the researchers found no major change in discard rates since the year 2000. However, recovery rates have decreased in recent years. In addition, fewer candidates have been added to the pancreas waiting list. This may be due in part to trends in transplant candidacy that may qualify diabetic candidates for a kidney transplant but not a pancreas, such as presence of type II diabetes, higher body-mass index and advanced age.

Sensitization Level at Retransplant Among Non-sensitized Pediatric Recipients of First Deceased Donor Kidney Transplants Not Affected by DR Mismatch Level
Embargo until Sunday, May 3 – 4:24 p.m. EDT
Authors: Wida S. Cherikh, Ph.D.*, Amber Wilk, Ph.D.*, Harrison McGehee, B.S.*, Eileen Brewer, M.D.

Immune sensitization for kidney transplantation, measured by a panel reactive antibody (PRA) level, assesses the likelihood of donor kidneys being biologically incompatible with the recipient due to immune system rejection. Sensitization can often be higher among candidates who received a previous kidney transplant that later failed. The risk of increased sensitization may be higher among recipients who had a greater mismatch among certain human leukocyte antigens (HLA) used to assess initial compatibility between the donor and recipient.

The researchers compared retransplant rates and level of immune system sensitization at first transplant among non-sensitized pediatric and adult kidney recipients over a 20-year period, to study whether HLA-DR mismatch affected sensitization at the time of repeat transplant. For recipients who were non-sensitized at the time of their first transplant, most received a kidney with one to two HLA-DR mismatches. Retransplant rates were similar (about 20 percent) among recipients of a kidney with zero, one or two DR mismatches.

For pediatric recipients, the sensitization level at repeat transplantation was not significantly associated with the level of DR mismatch. By contrast, for adult recipients, the level of DR mismatch was significantly associated with high sensitization for a repeat transplant; as the DR mismatch level increased, the risk of high sensitization also increased.

Results of Broader Sharing of Young Pediatric Liver Donor Lungs and Priority Allocation System for Young Pediatric Lung Candidates
Embargo until Sunday, May 3 – 4:48 p.m. EDT
Authors: Wida S. Cherikh, Ph.D.*, Amber Wilk, Ph.D.*, Gary Visner, D.O., Yulin Cheng*, Stuart Sweet, M.D.

The researchers compared transplant and survival data from periods before and after policy changes implemented in 2010 to increase geographic access and allocation priority for lung candidates younger than age 11.

Among candidates listed after the policy change, pediatric lung candidates did not have a significantly higher risk of death than adult candidates. The likelihood of transplantation for candidates age 5 and younger and those between age 12 and 17 was higher than that for adult candidates, while the likelihood of transplantation for candidates between age 6 and 11 was similar to that of adults. Most recipients age 11 or younger received transplants from donors in the same age group. One-year patient survival was comparable among all the recipient age groups.

Should Only Active Candidates Define the EPTS Top 20% in the New Kidney Allocation System?
Embargo until Sunday, May 3 – 5:12 p.m. EDT
Authors: Darren Stewart, M.S.*, Anna Kucheryavaya, M.S.*, Gena Boyle, M.P.A.*, Mark Aeder, M.D., Richard Formica, M.D.

The Estimated Post-Transplant Survival (EPTS) formula is used to identify kidney transplant candidates’ relative long-term need for a functioning transplant. Candidates with the 20 percent highest EPTS are likely to need a transplant the longest and are thus prioritized for kidneys with the longest estimated function.

An EPTS score is calculated for all adult kidney candidates, whether they are actively eligible for organ offers or are in an inactive status and may be reactivated at any time. The researchers analyzed characteristics of active and inactive candidates to study how the EPTS top 20 percent calculation might differ if limited to active candidates only.

Inactive candidates were less likely to have had a prior transplant than active candidates, but inactive candidates also tended to be older, have spent a longer time on dialysis and were more likely to be diabetic.

If only active candidates’ criteria were used to define the top 20 percent of EPTS, it would result in fewer but slightly healthier candidates receiving priority for high-longevity kidneys. While this change might improve the utility benefit of longevity matching, it may also narrow candidate access to the highest quality kidneys and thus should be considered carefully.

Emerging Strategies to Screen Kidney Offers Based on the Kidney Donor Profile Index (KDPI)
Embargo until Monday, May 4 – 5:30 p.m. EDT
Authors: Darren Stewart, M.S.*, Anna Kucheryavaya, M.S.*, Gena Boyle, M.P.A.*, Robert Metzger, M.D., Mark Aeder, M.D., Richard Formica, M.D.

The Kidney Donor Profile Index (KDPI) is a percentage formula that estimates the potential longevity of donor kidneys based on medical criteria. Kidney transplant programs can establish for each candidate a maximum acceptable KDPI value to be considered for an organ offer. The researchers studied maximum KDPI values entered for more than 9,700 transplant candidates at 142 kidney programs, as well as the centers’ acceptance rates of kidney offers.

While many programs tend to enter the most common values of either 85 percent or 100 percent for all of their candidates, a number of programs appear to be stratifying maximum acceptable KDPI values based on characteristics such as candidate age, local vs. import offers and whether the kidney offer is a zero-antigen mismatch. The researchers suggest that programs that are likely to refuse imported, higher-KDPI kidneys may benefit from setting lower maximum KDPI values for non-local offers. Effective use of this new screening tool can enhance the effectiveness and timeliness of organ placement and reduce kidney discard rates.

Efforts to Improve Living Kidney Donor Follow-up Reporting Have Been Successful
Embargo until Monday, May 4 – 5:30 p.m. EDT
Authors: Jennifer Wainright, Ph.D.*, Mary Amanda Dew, Ph.D., Claudine Lougee, B.A.*, Sarah Taranto*, Lee Bolton, M.S.N., ACNP*, Christie Thomas, M.B., FRCP, FASN, FAHA

In February 2013, the OPTN implemented minimum thresholds for living donor kidney transplant programs to report clinical and laboratory follow-up data on their donors. This information is important to assess potential donor risk and aid in informed consent for living kidney donation. The researchers studied comparable cohorts of follow-up data before and after the thresholds were established.

National rates of timely clinical data increased, from 26.5 percent for living donor kidney transplants performed in 2007 to 71.8 percent for transplants in 2013. Timely submission of lab data similarly increased, from 19.1 percent for transplants performed in 2007 to 66.5 percent for 2013 transplants. Few reports indicated that living kidney donors were unwilling to submit to follow-up.

The percentage of individual transplant programs meeting the reporting thresholds also continued to increase, with 76.1 percent meeting the requirement in 2013 for clinical data and 81.3 percent meeting the requirement for lab data. The majority of programs that missed the 2013 clinical data threshold needed five or fewer additional donor reports to meet it. The dramatic increase demonstrates transplant programs’ commitment and ability to improve follow-up reporting.

Kidney vs. Heart Calculated PRA (CPRA) for Sensitized Heart Candidates: Does Donor Ethnic Distribution Make a Difference?
Embargo until Monday, May 4 – 5:30 p.m. EDT
Authors: Anna Kucheryavaya, M.S.*, Liz Robbins Callahan, Esq.*, Leah Edwards, Ph.D.*

The calculated panel reactive antibody (CPRA) formula, used to assess the likelihood of donor kidney and kidney/pancreas offers being biologically incompatible with the recipient, takes into account the historic ethnic makeup of the kidney deceased donor population. Heart transplant professionals also use the kidney/pancreas CPRA calculator to estimate biological compatibility for some sensitized heart transplant candidates. The researchers studied differences in the ethnic population between kidney and heart donors to determine whether a heart-specific CPRA formula would provide more benefit to heart candidates.

Although there are significant differences in the ethnic distribution of kidney and heart deceased donors, the resulting difference in CPRA calculated values is relatively small. The researchers suggest that continuing to use the existing kidney and kidney/pancreas CPRA formula for heart candidates may be beneficial, to prevent either confusion among transplant clinicians as to which formula to use or potential differences in values for candidates who need both a heart and a kidney.

MELD/PELD 35+ Candidates Benefit from Regional Sharing
Embargo until Tuesday, May 5 – 4:12 p.m. EDT
Authors: Erick Edwards, Ph.D.*, Ann Harper*, Ryutaro Hirose, M.D., David Mulligan, M.D.

In 2013, the OPTN implemented a policy to increase regional access to liver transplants for high-urgency candidates – those with a score of 35 or higher using the Model for End-Stage Liver Disease (MELD) or Pediatric End-Stage Liver Disease (PELD) formula. The researchers studied waiting list and post-transplant outcomes for the one-year period before and after policy implementation.

Post-policy outcomes suggest expectations for the policy have largely been met. The percentage of transplants for candidates with a MELD/PELD of 35 or higher has increased, and the probability of death within 90 days without a transplant has decreased. The overall median distance livers traveled from donor to recipient location increased slightly, and the percentage of regional transplants increased, but organ preservation time remained largely unchanged. Liver discard rates dropped in the post-implementation era. The six-month patient survival rates were similar in the pre- and post-implementation era, as were patient survival rates among recipients with a MELD/PELD of 35 or higher. Longer-term results of the policy will continue to be monitored.

Reasons for Match Offer Refusals and Efforts To Reduce Them in the OPTN/UNOS Kidney Paired Donation Pilot Program
Embargo until Tuesday, May 5 – 5:00 p.m. EDT
Authors: Ruthanne Leishman, RN, M.P.H.*, Darren Stewart, M.S.*, Anna Kucheryavaya, M.S.*, Liz Robbins Callahan, Esq.*, Tuomas Sandholm, Ph.D., Mark Aeder, M.D.

The OPTN Kidney Paired Donation Pilot Program (KPDPP) has arranged more than 125 transplants since its launch in 2010. At the same time, only eight percent of matches identified through the program have resulted in a transplant. The researchers analyzed match offers over a nine-month period that did not result in a transplant, to explore ways to increase the efficiency of matches resulting in transplantation.

More than half the time, a “failed” match had been accepted by the candidate’s transplant hospital but could not proceed due to refusal of another match within the same exchange. Common reasons for refusals of matches included donor-specific antibodies, donor age or medical history, or another transplant opportunity identified for the candidate. Efforts to reduce refusal rates include further investigation of potentially avoidable refusals, optimizing the effectiveness of the program’s tool to pre-select acceptable donor criteria, developing a comprehensive set of program requirements for histocompatibility matching, and potential changes to the algorithm that could alert programs of potential match failures before they proceed.

Association of Transplant Volume and Survival in Pediatric Kidney Transplants
Embargo until Tuesday, May 5 – 5:30 p.m. EDT
Authors: Wida S. Cherikh, Ph.D.*, Amber Wilk, Ph.D.*, Christine Flavin, M.P.H.*, Eileen Brewer, M.D.

Center-specific volume (the number of transplants performed at an individual transplant center) has been shown to correlate with outcomes for many procedures in the adult population. The researchers studied the effect on transplant volume on survival for kidney transplants performed over a 10-year period for recipients younger than age 18. The OPTN Pediatric Transplantation Committee has recommended 12 as a minimal transplant volume that demonstrates pediatric training and expertise.

During the study period, 97 percent of the kidney transplants were performed at “high-volume” programs, defined as a program that performed at least 12 transplants for patients younger than age 18. The remaining 3 percent of the kidney transplants for patients younger than 18 were performed at programs categorized as “low-volume.”

The high-volume programs were associated with statistically significant higher outcomes five years after the transplant, both in graft and patient survival. This finding supports further investigation of minimal experience criteria for physicians and surgeons caring for pediatric kidney recipients.

CPRA Values Are Substantially Increased for Some Candidates Subsequent to Inclusion of Unacceptable C-locus Antigens While Listing Practices Remain Unchanged
Embargo until Tuesday, May 5 – 5:30 p.m. EDT
Authors: Anna Kucheryavaya, M.S.*, Robert Bray, Ph.D., Andrew Miller, Esq.,* Dolly Tyan, Ph.D.

The calculated panel reactive antibody (CPRA) formula, used to assess the likelihood of donor kidney and kidney/pancreas offers being biologically incompatible with the recipient, was amended in 2013 to include unacceptable antigens on the C-locus. Prior to the change, unacceptable C-locus antigens could be reported, but they were not reflected in the overall CPRA calculation. The researchers studied reporting of unacceptable C-locus antigens for kidney candidates and changes in CPRA values before and after the change in the CPRA calculation, to evaluate the impact of the revision.

While the percentage of kidney registrations reported with unacceptable C-locus antigens increased from 2006 to 2011, the rate of reporting has remained stable since the inclusion of these antigens in the CPRA formula. This suggests that many transplant centers did not change their reporting practices after the change. However, the CPRA values for some candidates were substantially increased. Since considerable allocation priority is offered to candidates with elevated CPRA values, accurate reporting of unacceptable antigens and inclusion of all unacceptable antigens into the CPRA calculation may help ensure these candidates receive appropriate consideration for compatible kidney offers.

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