Metformin use in kidney transplant recipients in the United States: an observational study

BACKGROUND/AIMS

Although metformin is contraindicated in patients with increased serum creatinine levels (≥1.5 mg/dl in men, ≥1.4 mg/dl in women) in the United States, its use has not been systematically examined in kidney transplant recipients. We aimed to determine the frequency of metformin use and its associations among kidney transplant recipients, and to assess allograft and patient survival associated with metformin use.

METHODS

In this retrospective cohort study, we linked Scientific Registry of Transplant Recipients data for all incident kidney transplants 2001-2012 and national pharmacy claims (n = 46,914). We compared recipients having one or more pharmacy claims for a metformin-containing product (n = 4,609) and recipients having one or more claims for a non-metformin glucose-lowering agent (n = 42,305).

RESULTS

On average, metformin claims were filled later after transplant and were associated with higher estimated glomerular filtration rates before the first claim. Median serum creatinine (mg/dl) levels before the first claim were lower in recipients with metformin claims than in those with non-metformin claims (1.3 [interquartile range 1.0-1.7] vs. 1.6 [1.2-2.5], respectively; p < 0.0001). Metformin was associated with lower adjusted hazards for living donor (0.55, 95% confidence interval 0.38-0.80; p = 0.002) and deceased donor (0.55, 0.44-0.70; p < 0.0001) allograft survival at 3 years posttransplant, and with lower mortality.

CONCLUSIONS

Despite metformin being contraindicated in renal dysfunction, many kidney transplant recipients receive it, and it is not associated with worse patient or allograft survival.

OPTN/SRTR 2013 Annual Data Report: heart

The number of heart transplants performed annually continues to increase gradually, and the number of adult candidates on the waiting list increased by 34.2% from 2003 to 2013. The heart transplant rate among active adult candidates peaked at 149.0 per 100 waitlist years in 2007 and has been declining since then; in 2013, the rate was 87.4 heart transplants per 100 active waitlist years. Increased waiting times do not appear to be correlated with an overall increase in waitlist mortality. Since 2008, the proportion of patients on life support before transplant increased from 53.4% to 65.8% in 2013. Medical urgency categories have become less distinct, with most patients listed in higher urgency categories. Approximately 500 pediatric candidates are added to the waiting list each year; the number of pediatric transplants performed each year increased from 293 in 2003 to 411 in 2013. Patient survival among pediatric recipients continues to improve; 5-year patient survival for transplants performed from 2001 through 2008 was 70% to 80%. Medicare paid for some or all of the care for 42.2% of all heart transplant recipients in 2012.

Diabetic kidney disease: a clinical update from Kidney Disease: Improving Global Outcomes

The incidence and prevalence of diabetes mellitus (DM) continue to grow markedly throughout the world, due primarily to the increase in type 2 DM (T2DM). Although improvements in DM and hypertension management have reduced the proportion of diabetic individuals who develop chronic kidney disease (CKD) and progress to end-stage renal disease (ESRD), the sheer increase in people developing DM will have a major impact on dialysis and transplant needs. This KDIGO conference addressed a number of controversial areas in the management of DM patients with CKD, including aspects of screening for CKD with measurements of albuminuria and estimated glomerular filtration rate (eGFR); defining treatment outcomes; glycemic management in both those developing CKD and those with ESRD; hypertension goals and management, including blockers of the renin-angiotensin-aldosterone system; and lipid management.

OPTN/SRTR 2013 Annual Data Report: economics

While the costs to Medicare of solid organ transplant are varied and considerable, the total Medicare expenditure of $4.4 billion for solid organ transplant recipients was less than 1 remains one of the most cost-effective surgical interventions in medicine. Heart transplant, the most expensive of the major transplants, is likely cost-effective; SRTR has released an Excel-based tool for investigators to use in exploring this question further. It is likely that most solid organ transplants are cost-effective, given the results presented here and the relatively high cost of heart transplant. However, this must be verified with further study.

OPTN/SRTR 2013 Annual Data Report: pancreas

Pancreas listings and transplants decreased during the past decade, most notably pancreas after kidney transplants. Center-reported outcomes of pancreas transplant across all groups, short-term and long-term, improved during the same period. Changes to the pancreas allocation system creating an efficient, uniform national system will be implemented in late 2014. Pancreas-alone and simultaneous pancreas-kidney (SPK) candidates will form a single match-run list with priority to most SPK candidates ahead of kidney-alone candidates to decrease waiting times for SPK candidates, given their higher waitlist mortality compared with nondiabetic kidney transplant candidates. The changes are expected to eliminate local variability, providing more consistent pancreas allocation nationwide. Outcomes after pancreas transplant are challenging to interpret due to lack of a uniform definition of graft failure. Consequently, SRTR has not published data on pancreas graft failure for the past 2 years. The Organ Procurement and Transplantation Network Pancreas Transplantation Committee is working on a definition that could provide greater validity for future outcomes analyses. Challenges in pancreas transplantation include high risk of technical failures, rejection (early and late), and surgical complications. Continued outcome improvement and innovation has never been more critical, as alternatives such as islet transplant and artificial pancreas move closer to clinical application.

Sirolimus use and cancer incidence among US kidney transplant recipients

Sirolimus has anti-carcinogenic properties and can be included in maintenance immunosuppressive therapy following kidney transplantation. We investigated sirolimus effects on cancer incidence among kidney recipients. The US transplant registry was linked with 15 population-based cancer registries and national pharmacy claims. Recipients contributed sirolimus-exposed time when sirolimus claims were filled, and unexposed time when other immunosuppressant claims were filled without sirolimus. Cox regression was used to estimate associations with overall and specific cancer incidence, excluding nonmelanoma skin cancers (not captured in cancer registries). We included 32,604 kidney transplants (5687 sirolimus-exposed). Overall, cancer incidence was suggestively lower during sirolimus use (hazard ratio [HR] = 0.88, 95% confidence interval [CI] = 0.70-1.11). Prostate cancer incidence was higher during sirolimus use (HR = 1.86, 95% CI = 1.15-3.02). Incidence of other cancers was similar or lower with sirolimus use, with a 26% decrease overall (HR = 0.74, 95% CI = 0.57-0.96, excluding prostate cancer). Results were similar after adjustment for demographic and clinical characteristics. This modest association does not provide strong evidence that sirolimus prevents posttransplant cancer, but it may be advantageous among kidney recipients with high cancer risk. Increased prostate cancer diagnoses may result from sirolimus effects on screen detection.

OPTN/SRTR 2013 Annual Data Report: intestine

Despite improvements in medical and surgical treatment of intestinal failure over the past decade, intestine transplant continues to play an important role. Of 171 new patients added to the intestine transplant waiting list in 2013, 49% were listed for intestine-liver transplant and 51% for intestine transplant alone or with an organ other than liver. The pretransplant mortality rate decreased dramatically over time for all age groups, from 30.3 per 100 waitlist years in 2002-2003 to 6.9 for patients listed in 2012-2013. The number of intestine transplants decreased from 91 in 2009 to 51 in 2013; intestine-liver transplants decreased from 135 in 2007 to a low of 44 in 2012, but increased slightly to 58 in 2013. Ages of intestine and intestineliver transplant recipients have changed substantially; the number of adult recipients was double the number of pediatric recipients in 2013. Graft survival improved over the past decade. Graft failure in the first 90 days posttransplant occurred in 14.1% of intestine recipients and in 11.2% of intestine-liver recipients in 2013. The number of recipients alive with a functioning intestine graft has steadily increased since 2002, to 1012 in 2013; almost half were pediatric intestine-liver transplant recipients.

OPTN/SRTR 2013 Annual Data Report: lung

Lungs are allocated to adult and adolescent transplant candidates (aged ⩾ 12 years) on the basis of age, geography, blood type compatibility, and the lung allocation score (LAS), which reflects risk of waitlist mortality and probability of posttransplant survival. In 2013, the most adult candidates, 2394, of any year were added to the list. Overall median waiting time for candidates listed in 2013 was 4.0 months. The preferred procedure remained bilateral lung transplant, representing approximately 70% of lung transplants in 2013. Measures of short-term and longterm survival have plateaued since the implementation of the LAS in 2005. The number of new child candidates (aged 0-11 years) added to the lung transplant waiting list increased to 39 in 2013. A total of 28 lung transplants were performed in child recipients, 3 for ages younger than 1 year, 9 for ages 1 to 5 years, and 16 for ages 6 to 11 years. The diagnosis of pulmonary hypertension was associated with higher survival rates than cystic fibrosis or other diagnosis (pulmonary fibrosis, bronchiolitis obliterans, bronchopulmonary dysplasia). For child candidates, infection was the leading cause of death in year 1 posttransplant and graft failure in years 2 to 5.

OPTN/SRTR 2013 Annual Data Report: deceased organ donation

The status of deceased organ donation is assessed using metrics such as donation/conversation rate, organ yield, and rate of organs recovered for transplant and not transplanted. These metrics are based on eligible deaths (brain death of a person aged 70 years or younger) as well as on actual donors. The 9132 eligible deaths reported in 2013 represented a slight increase over 2012. The donation/conversion rate was 71.3 eligible donors per 100 eligible deaths, a slight decline from 2012, and varied by donation service area from 50.0 to 87.0. The number of organs recovered per donor, 3.55, also varied by donation service area, from 2.79 to 4.10. The mean number of organs transplanted per donor was 3.08 in 2013, slightly higher than 3.02 in 2012. The mean observed/expected organ yield ratio for kidneys varied from 0.86 to 1.18; for pancreata, from 0.29 to 2.59; for livers, from 0.69 to 1.17; for hearts, from 0.68 to 1.41; and for lungs, from 0.33 to 1.41. The rate of organs recovered for transplant and not transplanted in 2013 for all organs combined was 0.13 per recovered organ, slightly lower than the rate of 0.14 in 2012.

OPTN/SRTR 2013 Annual Data Report: liver

During 2013, 10,479 adult candidates were added to the liver transplant waiting list, compared with 10,185 in 2012; 5921 liver transplants were performed, and 211 of the transplanted organs were from living donors. As of December 31, 2013, 15,027 candidates were registered on the waiting list, including 12,407 in active status. The most significant change in allocation policy affecting liver waitlist trends in 2013 was the Share 35 policy, whereby organs from an entire region are available to candidates with model for end-stage liver disease scores of 35 or higher. Median waiting time for such candidates decreased dramatically, from 14.0 months in 2012 to 1.4 months in 2013, but the effect on waitlist mortality is unknown. The number of new active pediatric candidates added to the liver transplant waiting list increased to 693 in 2013. Transplant rates were highest for candidates aged younger than 1 year (275.6 per 100 waitlist years) and lowest for candidates aged 11 to 17 years (97.0 per 100 waitlist years). Five-year graft survival was 71.7% for recipients aged younger than 1 year, 74.9% for ages 1 to 5 years, 78.9% ages 6 to 10 years, and 77.4% for ages 11 to 17 years.

OPTN/SRTR 2013 Annual Data Report: kidney

A new kidney allocation system, expected to be implemented in late 2014, will characterize donors on a percent scale (0%-100%) using the kidney donor profile index (KDPI). The 20% of deceased donor kidneys with the greatest expected posttransplant longevity will be allocated first to the 20% of candidates with the best expected posttransplant survival; kidneys that are not accepted will then be offered to remaining 80% of candidates. Waiting time will start at the time of maintenance dialysis initiation (even if before listing) or at the time of listing with an estimated glomerular filtration rate of 20 mL/min/1.73 m(2) or less. Under the current system, the number of candidates on the waiting list continues to increase, as each year more candidates are added than are removed. Median waiting times for adults increased from 3 years in 2003 to more than 4.5 years in 2009. Donation rates have not increased. Short-term outcomes continue to improve; death-censored graft survival at 90 days posttransplant was 97% or higher for deceased donor transplants and over 99% for living donor transplants. In 2013, 883 pediatric candidates were added to the waiting list; 65.8% of pediatric candidates on the list in 2013 underwent deceased donor transplant. Five-year graft survival was highest for living donor recipients aged younger than 11 years (89%) and lowest for deceased donor recipients aged 11 to 17 years (68%).

Cardiovascular risk assessment in kidney transplantation

Cardiovascular disease (CVD) remains the most common cause of death after kidney transplantation worldwide, with the highest event rate in the early postoperative period. In an attempt to address this issue, screening for CVD prior to transplant is common, but the clinical utility of screening asymptomatic transplant candidates remains unclear. A large degree of variation exists among both transplant center practice patterns and clinical practice guidelines regarding who should be screened, and opinions are based on mixed observational data with great potential for bias. In this review, we discuss the potential risks, benefits, and evidence for screening for CVD in kidney transplant candidates, and also the next steps to better evaluate and treat asymptomatic kidney transplant candidates.

Polycystic kidney disease and cancer after renal transplantation

Autosomal dominant polycystic kidney disease (ADPKD), the most common form of polycystic kidney disease (PKD), is a disorder with characteristics of neoplasia. However, it is not known whether renal transplant recipients with PKD have an increased risk of cancer. Data from the Scientific Registry of Transplant Recipients, which contains information on all solid organ transplant recipients in the United States, were linked to 15 population-based cancer registries in the United States. For PKD recipients, we compared overall cancer risk with that in the general population. We also compared cancer incidence in PKD versus non-PKD renal transplant recipients using Poisson regression, and we determined incidence rate ratios (IRRs) adjusted for age, sex, race/ethnicity, dialysis duration, and time since transplantation. The study included 10,166 kidney recipients with PKD and 107,339 without PKD. Cancer incidence in PKD recipients was 1233.6 per 100,000 person-years, 48% higher than expected in the general population (standardized incidence ratio, 1.48; 95% confidence interval [95% CI], 1.37 to 1.60), whereas cancer incidence in non-PKD recipients was 1119.1 per 100,000 person-years. The unadjusted incidence was higher in PKD than in non-PKD recipients (IRR, 1.10; 95% CI, 1.01 to 1.20). However, PKD recipients were older (median age at transplantation, 51 years versus 45 years for non-PKD recipients), and after multivariable adjustment, cancer incidence was lower in PKD recipients than in others (IRR, 0.84; 95% CI, 0.77 to 0.91). The reason for the lower cancer risk in PKD recipients is not known but may relate to biologic characteristics of ADPKD or to cancer risk behaviors associated with ADPKD.

Bayesian methods for assessing transplant program performance

Based on recommendations from a recent consensus conference and a report commissioned by the Centers for Medicare & Medicaid Services to the Committee of Presidents of Statistical Societies, the Scientific Registry of Transplant Recipients (SRTR) plans to adopt Bayesian methods for assessing transplant program performance. Current methods for calculating program-specific reports (PSRs) often generate implausible point estimates of program performance, wide confidence intervals and underpowered conventional statistical tests. Although technically correct, these methods produce statistical summaries that are prone to misinterpretation. The Bayesian approach assumes that performance of most programs is about average and few programs perform much better or much worse than average; thus, strong evidence is required to conclude that performance is extremely good or poor. In Bayesian statistics, inference is performed via a posterior probability distribution, which reflects both the available data and prior beliefs about what model parameter values are most likely. In the PSRs, the posterior distribution of a program-specific hazard ratio will show whether a program is likely to be performing better or worse than average. Bayesian-derived PSRs will be available for preview by programs on the private SRTR website in mid-2014 and will likely replace current methods for public reporting in early 2015.

A scientific registry of transplant recipients bayesian method for identifying underperforming transplant programs

In response to recommendations from a recent consensus conference and from the Committee of Presidents of Statistical Societies, the Scientific Registry of Transplant Recipients explored the use of Bayesian hierarchical, mixed-effects models in assessing transplant program performance in the United States. Identification of underperforming centers based on 1-year patient and graft survival using a Bayesian approach was compared with current observed-to-expected methods. Fewer small-volume programs (<10 transplants per 2.5-year period) were identified as underperforming with the Bayesian method than with the current method, and more mid-volume programs (10-249 transplants per 2.5-year period) were identified. Simulation studies identified optimal Bayesian-based flagging thresholds that maximize true positives while holding false positive flagging rates to approximately 5% regardless of program volume. Compared against previous program surveillance actions from the Organ Procurement and Transplantation Network Membership and Professional Standards Committee, the Bayesian method would have reduced the number of false positive program identifications by 50% for kidney, 35% for liver, 43% for heart and 57% for lung programs, while preserving true positives for, respectively, 96%, 71%, 58% and 83% of programs identified by the current method. We conclude that Bayesian methods to identify underperformance improve identification of programs that need review while minimizing false flags.

New national allocation policy for deceased donor kidneys in the United States and possible effect on patient outcomes

In 2013, the Organ Procurement and Transplantation Network in the United States approved a new national deceased donor kidney allocation policy that introduces the kidney donor profile index (KDPI), which gives scores of 0%-100% based on 10 donor factors. Kidneys with lower KDPI scores are associated with better post-transplant survival. Important features of the new policy include first allocating kidneys from donors with a KDPI≤20% to candidates in the top 20th percentile of estimated post-transplant survival, adding waiting time from dialysis initiation, conferring priority points for a calculated panel-reactive antibody (CPRA)>19%, broader sharing of kidneys for candidates with a CPRA≥99%, broader sharing of kidneys from donors with a KDPI>85%, eliminating the payback system, and allocating blood type A2 and A2B kidneys to blood type B candidates. We simulated the distribution of kidneys under the new policy compared with the current allocation policy. The simulation showed increases in projected median allograft years of life with the new policy (9.07 years) compared with the current policy (8.82 years). With the new policy, candidates with a CPRA>20%, with blood type B, and aged 18-49 years were more likely to undergo transplant, but transplants declined in candidates aged 50-64 years (4.1% decline) and ≥65 years (2.7% decline). These simulations demonstrate that the new deceased donor kidney allocation policy may improve overall post-transplant survival and access for highly sensitized candidates, with minimal effects on access to transplant by race/ethnicity and declines in kidney allocation for candidates aged ≥50 years.

Potential effects of reclassifying CKD as a coronary heart disease risk equivalent in the US population

BACKGROUND

Persons with chronic kidney disease (CKD) are at high risk for cardiovascular disease events, but are not classified as such in current US cholesterol treatment guidelines. We examined potential effects of modified guidelines in which CKD was considered a "coronary heart disease (CHD) risk equivalent" for risk stratification.

STUDY DESIGN

Nationally representative cross-sectional study.

SETTING & PARTICIPANTS

4,823 adults 20 years or older from the 2007-2010 National Health and Nutrition Examination Survey.

PREDICTORS

Cardiovascular risk stratification based on current US cholesterol treatment guidelines and 2 simulated scenarios in which CKD stages 3-5 or CKD stages 1-5 were considered a CHD risk equivalent.

OUTCOMES & MEASUREMENTS

Proportion of persons with low-density lipoprotein (LDL) cholesterol at levels above treatment targets and above the threshold for lipid-lowering therapy initiation, based on current guidelines and the 2 simulated scenarios.

RESULTS

Under current guidelines, 55.1 million adults in 2010 did not achieve the target LDL cholesterol goal. Of these, 25.2 million had sufficiently elevated levels to meet recommendations for initiating lipid-lowering therapy; 12.1 million were receiving this therapy but remained above goal. When CKD stages 3-5 were considered a CHD risk equivalent, 59.2 million persons were above target LDL cholesterol goals, with 28.5 million and 13.3 million meriting therapy initiation and intensification, respectively. When CKD stages 1-5 were considered a CHD risk equivalent, 65.2 million adults were above goal, with 33.9 million and 14.4 million meriting therapy initiation and intensification, respectively.

LIMITATIONS

CKD and LDL cholesterol defined using a single laboratory value.

CONCLUSIONS

Many adults in the United States currently do not meet recommended goals for LDL cholesterol levels. Modifying the current cholesterol guidelines to include CKD as a CHD risk equivalent would lead to a substantial increase in both the number of persons with levels above LDL cholesterol treatment targets and those recommended to initiate lipid-lowering therapy.

Survival of recipients of livers from donation after circulatory death who are relisted and undergo retransplant for graft failure

Use of grafts from donation after circulatory death (DCD) as a strategy to increase the pool of transplantable livers has been limited due to poorer recipient outcomes compared with donation after brain death (DBD). We examined outcomes of recipients of failed DCD grafts who were selected for relisting with regard to waitlist mortality and patient and graft survival after retransplant. From the Scientific Registry of Transplant Recipients database, we identified 1820 adults who underwent first deceased donor liver transplant January 1, 2004 to June 30, 2011, and were relisted due to graft failure; 12.7% were DCD recipients. Compared with DBD recipients, DCD recipients had better waitlist survival (90-day mortality: 8%, DCD recipients; 14-21%, DBD recipients). Of 950 retransplant patients, 14.5% were prior DCD recipients. Graft survival after second liver transplant was similar for prior DCD (28% graft failure within 1 year) and DBD recipients (30%). Patient survival was slightly better for prior DCD (25% death within 1 year) than DBD recipients (28%). Despite higher overall graft failure and morbidity rates, survival of prior DCD recipients who were selected for relisting and retransplant was not worse than survival of DBD recipients.

BP, cardiovascular disease, and death in the Folic Acid for Vascular Outcome Reduction in Transplantation trial

The optimal BP level in kidney transplant recipients remains uncertain. This post hoc analysis of the Folic Acid for Vascular Outcome Reduction in Transplantation (FAVORIT) trial cohort assessed associations of BP with a pooled cardiovascular disease (CVD) outcome and with all-cause mortality. In 3474 prevalent kidney transplant patients, mean age was 52±9 years, 63% were men, 76% were white, 20% had a history of CVD, 40% had a history of diabetes mellitus, and the median time since transplant was 4.1 years (25th to 75th percentiles, 1.7-7.4); mean systolic BP was 136±20 mmHg and mean diastolic BP was 79±12 mmHg. There were 497 CVD events and 406 deaths. After adjustment for demographic and transplant characteristics and CVD risk factors, each 20-mmHg increase in baseline systolic BP associated with a 32% increase in subsequent CVD risk (hazard ratio [HR], 1.32; 95% confidence interval [95% CI], 1.19 to 1.46) and a 13% increase in mortality risk (HR, 1.13; 95% CI, 1.01 to 1.27). Similarly, after adjustment, at diastolic BP levels<70 mmHg, each 10-mmHg decrease in diastolic BP level associated with a 31% increase in CVD risk (HR, 1.31; 95% CI, 1.06 to 1.62) and a 31% increase in mortality risk (HR, 1.31; 95% CI, 1.03 to 1.66). However, at diastolic BP levels>70 mmHg, there was no significant relationship between diastolic BP and outcomes. Higher systolic BP strongly and independently associated with increased risk of CVD and all-cause mortality, without evidence of a J shape, whereas only lower levels of diastolic BP associated with increased risk of CVD and death in this trial.

New quality monitoring tools provided by the Scientific Registry of Transplant Recipients: CUSUM

The Scientific Registry of Transplant Recipients (SRTR) has been providing data on transplant program performance through semi-annual release of program-specific reports (PSRs). A consensus conference held in February 2012 recommended that SRTR also supply transplant programs with tools such as the cumulative sum (CUSUM) technique to facilitate quality assessment and performance improvement. SRTR developed the process, methodologies, programming code and web capabilities necessary to bring the CUSUM charts to the community, and began releasing them to all liver, kidney, heart and lung programs in July 2013. Observed-minus-expected CUSUM charts provide a general picture of a program's performance (all-cause graft failure and mortality within the first-year posttransplant) over a 3-year period; one-sided charts can determine when performance appears to be sufficiently worrisome to warrant action by the program. CUSUM charts are intended for internal quality improvement by allowing programs to better track performance in near-real time and day to day, and will not be used to indicate whether a program will be flagged for review. The CUSUM technique is better suited for real-time quality monitoring than the current PSRs in allowing monthly outcomes monitoring and presenting data recorded as recently as 2 months before the release of the CUSUM charts.

The role of procurement biopsies in acceptance decisions for kidneys retrieved for transplant

BACKGROUND AND OBJECTIVES

There is a shortage of kidneys for transplant, and many patients on the deceased donor kidney transplant waiting list would likely benefit from kidneys that are currently being discarded. In the United States, the most common reason given for discarding kidneys retrieved for transplant is procurement biopsy results. This study aimed to compare biopsy results from discarded kidneys with discard attributed to biopsy findings, with biopsy results from comparable kidneys that were successfully transplanted.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In this retrospective, observational, case-control study, biopsy reports were examined from 83 kidneys discarded in 2010 due to biopsy findings (cases), 83 contralateral transplanted kidneys from the same donor (contralateral controls), and 83 deceased donors randomly matched to cases by donor risk profile (randomly matched controls). A second procurement biopsy was obtained in 64 of 332 kidneys (19.3%).

RESULTS

The quality of biopsy reports was low, with amounts of tubular atrophy, interstitial inflammation, arteriolar hyalinosis, and acute tubular necrosis often not indicated; 69% were wedge biopsies and 94% used frozen tissue. The correlation between first and second procurement biopsies was poor; only 25% of the variability (R(2)) in glomerulosclerosis was explained by biopsies being from the same kidney. The percentages of glomerulosclerosis overlapped substantially between cases, contralateral controls, and randomly matched controls: 17.1%±15.3%, 9.0%±6.6%, and 5.0%±5.9%, respectively. Of all biopsy findings, only glomerulosclerosis>20% was independently correlated with discard (cases versus contralateral controls; odds ratio, 15.09; 95% confidence interval, 2.47 to 92.41; P=0.003), suggesting that only this biopsy result was used in acceptance decisions. One-year graft survival was 79.5% and 90.7% in contralateral and randomly matched controls, respectively, versus 91.6% among all deceased donor transplants in the Scientific Registry of Transplant Recipients.

CONCLUSIONS

Routine use of biopsies could lead to unnecessary kidney discards.

The kidney allocation system

The current kidney allocation system for transplants is outdated and has not evolved to reflect the changing demographics of patients on the waiting list. This article proposes a new system for kidney allocation, which more appropriately incorporates the biology of highly sensitized patients into the waiting-time scoring algorithm. This system will significantly reduce mismatches between possible donor kidney longevity and life expectancy of recipients, and makes incremental advances toward more geographic sharing. The proposed system makes significant progress toward eliminating deficiencies in the current system, and has the potential to increase the supply of available kidneys.