STANDARDS FOR EVALUATING OBESITY IN KIDNEY TRANSPLANT CANDIDATES
Standards for Evaluating Obesity in Kidney Transplant Candidates
Oregon Health & Science University
Pamela Haskell, Brittany Sansone, Heidi Schultz
June 15, 2010
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STANDARDS FOR EVALUATING OBESITY IN KIDNEY TRANSPLANT CANDIDATES
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Significance
Many factors impact the outcome of kidney transplantation. Obesity is one of the more controversial but
modifiable risk factors for poor outcomes. Meier-Kriesche, et al indicates that obesity as described by body
mass index (BMI) has a strong correlation with post-transplant outcomes.1 Obesity appears to influence
delayed graft failure, post-transplant diabetes mellitus and wound complications.2 Among transplant centers in
the United States there is no standardization regarding how to define obesity in adult kidney transplant
candidates and at what level obesity becomes a relative or absolute contraindication. Inconsistent definitions of
obesity will impact which candidates receive a transplant. The clarification of obesity standards will support
consistent decisions about kidney transplant eligibility and will support more reliable research about kidney
transplant outcomes at various levels of overweight and obesity.
Specific Aims and Hypothesis
Goal: To identify standards used to define obesity in kidney transplant candidates in the United States.
Primary Specific Aim: We propose to survey transplant dietitians to identify the methods and standards used
to define obesity as a relative contraindication for kidney transplant candidates.
Hypothesis: It is anticipated that greater than 50% of transplant dietitians will report using a BMI ≥35 kg/m2 to
define obesity as a relative contraindication when evaluating kidney transplant candidates.
Background
According to the United States Renal Data System (USRDS), at the end of 2007 more than 341,000
end-stage renal disease (ESRD) patients were receiving hemodialysis therapy, 26,340 were on peritoneal
dialysis, and 158,739 had a functioning transplanted kidney or graft. The transplant population has seen
significant growth, increasing 5.0-6.0 percent each year since 2001.4 Significant increases in co-morbid
conditions such as hypertension and diabetes, both of which increase the risk of chronic kidney disease (CKD),
are possible explanations for the increase in kidney transplants. For most patients with ESRD, kidney
transplantation is regarded as the treatment with the best outcomes in those who receive the transplantation
before long-term dialysis begins.5 Many kidney transplant candidates present as overweight or obese: One
STANDARDS FOR EVALUATING OBESITY IN KIDNEY TRANSPLANT CANDIDATES
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study found that the fraction of kidney transplant patients with a normal BMI (18-24.9 kg/m2) decreased
by 41.9%. At the same time there was a 32% increase in patients with a BMI of 25 to 29.9 kg/m2, and a 116%
increase in patients with a BMI >30 kg/m2 who received kidney transplants in 2001 compared to those who
were transplanted in 1988.6 Research has demonstrated that obese transplant recipients are at greater risk for
complications post-transplantation.7
Standard classifications of obesity are clearly defined by the National Institute of Health (NIH) however
the application of these standards in kidney transplant evaluations is inconsistent and not well described.
Without a clear understanding of how obesity standards are applied to the evaluation of kidney transplant
candidates, determining an exclusion criteria and evaluating kidney transplant outcomes based on obesity is
complicated. As previously mentioned, renal transplantation is the ideal treatment for patients with ESRD.
However, a limited number of available organs force candidates to be selected based on their likelihood of
having positive outcomes. One recommendation is that the upper limit for candidacy be extended to cover
patients with a BMI of 40 kg/m2.8 In the medical community, it is a commonly held belief that obese patients
will have poorer outcomes than their non-obese counterparts. Dindo, et al found no compelling evidence to
validate this belief and suggests that this mentality be reconsidered in the renal transplant community.9 There
are two significant consequences of this mentality for transplant candidates: First, the median time to receive a
kidney transplant was found to increase as BMI category increased.10 Candidates at higher BMI categories
were often less likely to be given consideration for an organ by a transplant center.10 Second, some obese
patients who might benefit from a transplant are being dismissed if they are considered too great a medical risk
and/or financial cost. Finally, there is a trend in reverse epidemiology in dialysis patients. The literature reports
obese dialysis patients with lower morbidity when compared to patients classified as normal weight or
overweight. This may support higher body mass index (BMI) cut-offs for transplant candidates.11 Therefore, a
better understanding of current practices to define obesity cut off points in candidates for kidney transplant may
have significant implications for treatment and care of this patient population.
This is a cross-sectional study to determine the standards used to measure and define obesity in
kidney transplant candidates at transplant centers in the United States. This data will provide a framework that
STANDARDS FOR EVALUATING OBESITY IN KIDNEY TRANSPLANT CANDIDATES
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describes methods used in practice by registered dietitians (RDs) and other transplant team members who
work with the ESRD population.
Methods
Survey Development – Pilot
No standard instruments exist to evaluate the topic of interest so a survey questionnaire was
developed. A pilot survey containing fifteen questions was distributed via Survey Monkey to twelve RDs that
have a history of work experience with renal transplant patients. Pilot participants provided feedback within the
survey through open text form after each question. All responses were anonymous. The pilot survey
questions covered demographics, credentials, years of experience, Renal Network Number, and specific
questions on work involved as a transplant dietitian. Data and feedback from the pilot survey were used to
develop the final questionnaire. The study protocol, pilot survey, and final survey were reviewed and approved
by the Oregon Health & Science University (OHSU) Institutional Review Board (IRB).
Survey Development – Actual
Using Survey Monkey, an online survey was developed and distributed to two groups. In the first case,
a link was sent via email to the managers of 249 transplant centers in the United States with a request that the
Transplant Administrator at each center distribute the survey to the center’s transplant dietitians. The survey
was also sent to the Renal RD listserv with a request that transplant dietitians should complete the survey, with
a caution not to duplicate a response that may already have been sent via the Transplant Administrators’
listserv. Survey completion takes time and effort, therefore survey fatigue and incomplete surveys were
anticipated. To limit these potential problems the survey created was short, easy to complete and targeted
dietitians who were most qualified to answer the questionnaire. To obtain the maximum participation, a
reminder email was sent on the fifteenth day and the twenty-fifth day after posting. The survey was closed
after five weeks and data were analyzed and compiled. Demographics of the transplant dietitian and their
application of MNT for kidney transplant patients were also collected.
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Subjects
The target population for this questionnaire was transplant RDs, including men and women who
currently work with adult kidney transplant candidates. The questionnaire excludes transplant dietitians that
work solely with heart, liver, pancreas, lung and/or intestine transplants. Most responses were received
through the RenalRD listserv. This listserv has 1700 subscribers and the National Kidney Foundations Council
on Renal Nutrition Membership surveys indicate that 2% of the subscribers are transplant RDs, suggesting that
34 transplant dietitians may be enrolled in the RenalRD listserv. Participants were also contacted by sending
an email and survey link to transplant administrators. Initial contact was through email and consent was
obtained within the Survey Monkey questionnaire.
Data Analysis
Demographic information was collected and analyzed using means and standard deviations.
Percentages, comparisons, and trends of anthropometric data used during pre-transplant evaluation among
different transplant network areas were also compiled.
Results
Absolute Exclusion
28
30
Number of Respondents
Relative Contraindication
25
18
20
17
15
10
5
7
3
1
1
2
21
32
1
36
37
38 38.5 39
1
1
1
1
11
41
42
NA
0
30
32
33
34
35
40
BMI
Figure 1. BMI values that RDs use for obesity as a relative or absolute contraindication for transplant consideration (n=46).
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A total of 55 transplant dietitians responded to the survey; all responses are included in our analysis.
Calculated BMI is used by 98% of respondents to determine obesity. As hypothesized, when BMI is used to
determine absolute exclusion, 39% of respondents reported absolute exclusion at a BMI of 35 kg/m2, 15% at a
BMI between 36-39, and 43% for a BMI ≥40kg/m2 (Figure 1). When BMI is used as a relative contraindication,
61% of respondents reported using BMI cutoffs at 35 kg/m2 and 15% at 40 kg/m2. Comparatively, in Europe,
a BMI >30 is the cut-off and in Japan a BMI >25 is often utilized as the cut-off point.12
Methods and measures used to evaluate obesity showed that registered nurses (RNs) in the transplant
centers are most likely to record the stated height, stated weight, and measured height. Most likely this occurs
during a telephone interview upon referral for transplant. RDs are most likely to record the measured weight
and calculate BMI at a clinic visit during the formal evaluation. Measurements such as waist circumference, hip
circumference, waist/hip ratio, bio-impedance analysis (BIA), and dual energy x-ray absorptiometry (DEXA)
measurements are not used consistently to evaluate obesity, BIA and DEXA are never used. The most
common measurement used is BMI with 98% of respondents reporting its usage, followed by waist
circumference (15%), hip circumference (2%), and waist/hip ratio (4%) indicated by the respective
percentages.
Since little has been published about demographics of kidney transplant dietitians, the survey included
questions about the job description of the transplant RD regarding pre- and post-transplant care. It was
revealed that 89% of respondents are involved in the nutrition component of the evaluation for transplant
candidacy. In addition to the nutrition evaluation that is part of the pre-transplant workup, respondents also
reported providing medical nutrition therapy (MNT) to pre-transplant patients. 58% indicated that MNT is
provided for weight management; 44% for chronic kidney disease (CKD), and 42% for diabetes mellitus (DM)
and/or heart healthy diet education. Only 15% participate in their center’s pre-transplant class; 11% reported
that they do not provide pre-transplant MNT.
Responses regarding post-transplant involvement revealed that 67% provide inpatient MNT, 56% are
involved to assist with weight management, 53% perform DM and/or heart healthy diet education, and 36%
provide CKD MNT. 13% of respondents are not involved in any form of post-transplant MNT within the first two
months after a transplant.
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Table 1. Demographic Characteristics by total sample (n= 55)
Characteristic
Valuea
Gender
Male
1.8
Female
98.2
Credentialsb
RD
100
LD/CDN
36.4
Master’s
38.2
PhD
1.8
RN
0.0
CSR
9.1
CDE
5.5
CNSC
10.9
Years of Practice
0-1
>1-3
>3-7
>7-10
>10-15
>15
1.8
3.6
23.6
10.9
12.7
47.3
a
Values are number (percentage) unless otherwise indicated.
Registered Dietitian, Licensed Dietitian/Certified Dietitian Nutritionist, Master’s (MS), Doctor of Philosophy, Registered Nurse,
Board Certified Specialist in Renal Nutrition, Certified Diabetes Educator, and Certified Nutrition Support Clinician.
b
Demographic information collected (Table 1) revealed that 98% of participants are female and 100%
are registered dietitians. Approximately one-third of respondents are licensed dietitians and/or certified dietitian
nutritionists, and one-third have a Master’s degree. Only 5% of RDs reported practicing as a dietitian for three
years or less, while 47% have been practicing for greater than fifteen years. There was no significant
difference in the amount of time having worked with dialysis patients—the range was from less than 1 year to
greater than 15 years. Approximately one-third of respondents have worked as a transplant RD between 1 and
3 years. In addition to working with kidney transplant patients, over half of respondents work with pancreas
transplants, and greater than one-third work with liver transplants.
There was no significant difference in the amount of full-time employee status devoted to a kidney
transplant center, however the RD services are mostly funded by the transplant program. These results were
confirmed when subjects were asked to describe their perceived role on the kidney transplant team. Some
described the level of respect of the dietitian for nutrition assessment and intervention. It was repeatedly noted
that the dietitian is valued as the nutrition expert. Three out of forty-five respondents who completed a question
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on how the RD is regarded within the team commented that their role on the team is minimal and that
becoming a valued member is a slow process. Finally, 72% of the respondents report that they attend and
participate in multi-disciplinary discussions at selection conferences and 83% document their nutrition
assessment and evaluation of the transplant candidate in the medical record.
.
Recommendations
This was a small sample study meant to advocate for further research in this area. Without studies to
measure the effectiveness of one obesity cut-off point over another, transplant centers are selecting numbers
that they feel will support a high success rate. The results of this study show a significant number of centers
using a BMI cut-off of either 35 or 40. Therefore, the next step is to determine which cut-offs produce better
outcomes and this would provide evidenced-based data to support the medical decisions surrounding the
evaluation of an obese transplant candidate. This could also potentially influence the amount and type of MNT
provided during the pre-transplant evaluation.
The data about the job functions of transplant dietitians provide interesting insight into many aspects of
their work, including possible under-utilization of Medicare funding for MNT for CKD in the pre- and posttransplant settings. Further study of this topic would be helpful.
Limitations
This study has several important limitations: First, our subject criteria were not randomly selected since
our objective was to obtain responses from the maximum number of kidney transplant dietitians possible, while
also limiting responses to one per transplant center. Second, it was unclear what percentage of transplant RDs
were reached. Survey administration efforts were complicated by the following unknowns: First, some RDs
might work at the same transplant center; second, some transplant centers were likely to be unrepresented;
finally, some emails may not have been read and/or the survey link may never have been opened. The survey
was also sent to the third party administrator, who forwarded the email and survey link to transplant
administrators, who were asked to forward it on to RDs in their transplant center. We were unable to verify if
the RDs received the survey. Additional limitations include the following: Participants didn’t know our exclusion
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criteria - thus we had one response from a pediatric transplant RD and one response from an RD in Canada.
Some transplant centers were not represented. The response rate, with 55 surveys completed, was lower than
expected, and the percent response was unknown. Email fatigue may have diminished the response rate. In
summary, the study was effective in producing introductory information which ultimately supported our
hypothesis; however it was not without limitations.
Future Directions
The results of this study provide a valuable framework to examine how obesity is defined among kidney
transplant centers in the United States. Future studies should determine how to identify and reach more
transplant dietitians. It is anticipated that this study will serve as an influence in the standardization of obesity
cut-off points among the U.S. kidney transplant centers. There is also some evidence that transplant dietitians
may benefit from education regarding Medicare’s MNT benefits as they can support MNT in pre- and posttransplant ESRD patients.
Acknowledgment
The authors would like to thank the following for their support: Maureen McCarthy, MPH, RD – Principle
Investigator; Tracy Ryan-Borchers, PhD, RD – Project Support; Tim Stevens, RN, BSN, CCTC – Project
Support; Diane Stadler, PhD, RD – Project Support; and Jackilen Shannon, PhD, RD – Project Support.
Financial Disclosures
This project was not financially supported by grants/organizations. Survey Monkey was paid for by Maureen
McCarthy, MPH, RD. The contents of this study are solely the responsibility of the dietetic interns and do not
necessarily represent the view of Oregon Health and Science University.
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References
1. Meier-Kriesche HU, Arndorfer JA, Kaplan B. The Impact of Body Mass Index on Renal Transplant
Outcomes: A Significant Independent Risk Factor for Graft Failure and Patient Death. Transplantation:
2002;73(1):70-74.
2. Kent PS. Issues of Obesity in Kidney Transplantation. Journal of Renal Nutrition. 2007; 17(2):107-113.
3. Fry K, Patwardhan A, Ryan C, Trevillian P, Chadban S, Westgarth F, Chan M. Development of EvidenceBased Guidelines for the Nutritional Management of Adult Kidney Transplant Recipients. Journal of Renal
Nutrition: 2009;19(1):101-104.
4. United States Renal Data System. Treatment Modalities in Volume Two: Atlas of End-Stage Renal Disease
(4). Retrieved from http://www.usrds.org/2009/pdf/V2_04_09.PDF.
5. Abecassis M, Bartlett ST, Collins AJ, Davis CL, Delmonico FL, Friedewald JF, Hays R, Howard A, Jones E,
Leichtman AB, Merion RM, Metzger RA, Pradel F, Schweitzer EJ, Velez RL, Gaston RS. Kidney
Transplantation as Primary Therapy for End-Stage Renal Disease: A National Kidney Foundation/Kidney
Disease Outcomes Quality Initiative (NKF/KDOQITM) Conference. Clin J Am Soc Nephrol. 2008; 3; 471480.
6. Kalil RS, Hunsicker LG. The Disadvantage of Being Fat. J Am Soc Nephrol. 2008; 19; 191-193.
7. Chang SH, Coates PTH, McDonald SP. Effects of Body Mass Index at Transplant on Outcomes of Kidney
Transplantation. Transplantation. 2007; 84(8); 981-987.
8. Jindal RM, Zawada ET. Obesity and Kidney Transplantation. Amer J Kid Dis. 2004; 43(6); 943-952.
9. Dindo D, Muller MK, Weber M, Clavien PA. Obesity in general elective surgery. Lancet. 2003; 361; 203235.
10. Segev DL, Simpkins CE, Thompson RE, Locke JE, Warren DS, Montgomery RA. Obesity Impacts Access
to Kidney Transplantation. J Am Soc Nephrol. 2008; 19; 349-355.
11. Kalantar-Zadeh K, Abbott KC, Salahudeen AK, Kilpatrick RD, Horwich TB. Survival advantages of obesity
in dialysis patients. Am J Clin Nutr. 2005; 81:543-54.
12. Maureen McCarthy, MPH, RD. Statement provided based on conversations at International Congress on
Renal Nutrition and Metabolism, May 25-28th, 2010.