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Costs and Outcomes of Privately-Insured Kidney Transplant Recipients by Body Mass Index | OMICS International
ISSN: 2161-0959
Journal of Nephrology & Therapeutics

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Costs and Outcomes of Privately-Insured Kidney Transplant Recipients by Body Mass Index

Patrick M Ercole1*, Paula M Buchanan2, Krista L Lentine2,3, Thomas E Burroughs2, Mark A Schnitzler2 and Kian A Modanlou4

1Goldfarb School of Nursing, Barnes-Jewish College, St. Louis, MO, USA

2Center for Outcomes Research, Saint Louis University, St. Louis, MO, USA

3Division of Nephrology, Saint Louis University School of Medicine, St. Louis, MO, USA

4Division of Transplantation, University of Tennessee / Methodist Transplant Institute, Memphis, TN, USA

*Corresponding Author:
Patrick M Ercole
4483 Duncan Ave, Mailstop 90-36-697
Saint Louis, MO 63110
Tel: 314-454-7538
E-mail: [email protected]

Received Date: December 09, 2011; Accepted Date: January 16, 2012; Published Date: January 18, 2012

Citation:Ercole PM, Buchanan PM, Lentine KL, Burroughs TE, Schnitzler MA, et al. (2012) Costs and Outcomes of Privately-Insured Kidney Transplant Recipients by Body Mass Index. J Nephrol Therapeutic S4:003. doi:10.4172/2161-0959.S4-003

Copyright: ©2012 Ercole PM, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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Keywords

Renal transplantation; Body mass index; Obesity; Outcomes; Cost

Introduction

The obesity epidemic in the United States has tempered progress in health outcomes made during the past several decades [1-5]. Studies have documented that operating on obese patients leads to longer and more difficult operations with greater complications [6- 8]. Furthermore, the requirement to report outcomes and the push to contain costs may lead to shying away from operating on patients who are perceived as having the potential for worse outcomes and increased costs of care.

Reports queried from national databases have confirmed that the prevalence of obese patients added to the kidney transplant (KT) waiting list has sharply increased over the last several years [9-11]. Although there is disagreement, studies have shown that obese recipients can improve survival compared to continued dialysis despite increased risks of mortality and peritransplant complications including delayed graft function, elevated transplant costs, and allograft loss [12-20]. Although benefits of kidney transplantation have been demonstrated among obese dialysis patients, registry-based analyses indicate that overweight and obese transplant candidates are less likely to receive an organ offer than candidates with normal body mass index (BMI) and are more likely to be bypassed when an organ becomes available [11,14].

Inpatient hospital days are the largest contributor to costs in KT [21]. Furthermore, an increased length of hospitalization post-KT has been shown to predict inferior graft and patient survival [22]. The aim of this study was to assess the impact of recipient BMI on the outcome and cost of KT in the first three years posttransplant in a private healthcare system. We examined a novel database linking Organ Procurement and Transplantation Network (OPTN) identifiers for a national sample of renal allograft recipients to administrative data from a private insurance provider. The methods and dataset used in this study replicate previously reported research [23-25].

Methods

Study sample

Upon approval from the institutional review board at Saint Louis University, records from the OPTN, which is overseen by the Health Resources and Services Administration (HRSA), were merged with clinical claim data from a large, private U.S. health insurance provider to form the retrospective cohort of this study. The link between the two sources was made using name, Social Security number, date of birth, and gender. The dataset was limited and de-identified prior to analysis in compliance with the Health Insurance Portability and Accountability Act (HIPAA).

The sample included all adult (age ≥18 years old) cadaveric-donor renal transplant recipients in the dataset from 2000 to 2007. Individuals with multiple-organ transplants or previous transplants were excluded. Recipients were excluded if the total charges of initial transplant hospitalization failed to exceed $30,000.

Definitions and assumptions

BMI was calculated using measurements at time of transplant. BMI groups followed selected cutoffs from World Health Organization (WHO) International Classifications [26]: underweight (<18.50 kg/m2), normal (18.50 – 25.00), and overweight (25.00 – 29.99). WHO obese (≥30.00) sub classifications were used to further stratify BMI for analysis into obese (30.00 – 34.99), morbidly obese (35.00 – 40.00), and extremely morbidly obese (≥40.00). Recipients with a BMI of less than 10 or greater than 70 were excluded from analysis as invalid outliers.

The primary outcome of interest was posttransplant cost, defined as charges on billing claims submitted to the insurance provider. Claims following recipient transplant were summed during transplant hospitalization as well as each of three years following transplantation. Charges from recipient dialysis center, health providers, and treatment centers comprised costs. All costs were adjusted for inflation with the medical component of the consumer price index using 2004 as the base year.

All claims were included from the date of transplantation until three years of follow-up, death, or end of study date (December 31, 2007). Recipients with incomplete follow-up data due to loss of insurance coverage or end of study within an interval of analysis were excluded from that and subsequent intervals. Recipients who died were included in the interval of analysis and had all charges following death set to zero dollars. In the instance where time between transplant and the end of study date was less than the follow-up time, posttransplant cost was set to missing.

Hospitalization for a kidney transplant was indicated using a diagnosis-related group (DRG) code of “302.” Study cost estimates summed all transplant and posttransplant claims until censoring (after which was set to zero dollars). Transplant hospitalization costs were summed from the date of transplant to ninety days following transplant. Posttransplant costs at one-, two- and three-year follow-up times were summed from transplant hospitalization to the end of the time interval.

Secondary outcomes of interest included delayed graft function (DGF), graft failure, patient survival, and length of transplant hospitalization. DGF indicates the organ does not immediately perform properly following transplantation. Graft failure includes the outcome of patient death.

The analysis included covariates on patient gender, race, ethnicity, age at transplant, primary cause of end-stage renal disease (ESRD), pre-transplant dialysis duration, diabetes, and peripheral vascular disease (PVD). Donor-related covariates were donor gender, race, age, BMI category, stroke cause of death, terminal creatinine ≥1.5 mg/dL, history of hypertension, diabetes, and sero-positive cytomegalovirus (CMV). Transplant-related covariates included donor type (standardand expanded- criteria donor [SCD, ECD] and donation after cardiac death [DCD]), peak panel reactive antibody (PRA) percentage, donorrecipient CMV sero-pairing, number of human leukocyte antigens (HLA) mismatches, sensitization, cold ischemia time, and year of transplant.

Statistical analysis

Unadjusted mean costs, presence of DGF, length of transplant hospitalization as well as recipient, donor, and transplant characteristics between BMI categories were examined for association using the nonparametric Kruskal-Wallis method of one-way analysis of variance by ranks for continuous variables. Post-hoc comparisons were made using Wilcoxon rank sum test with a continuity correction. Chi-square analysis, or a Monte Carlo estimate for Fisher’s exact test for small expected cell size, were used to analyze the independence of categorical variables by BMI levels. Multivariate linear regression analysis was utilized to examine costs within each interval of interest according to BMI category while adjusting for the study covariates. Graft failure and patient survival were estimated using the Kaplan-Meier method. Cox proportional hazards analysis, both full and stepwise models, was used to measure the adjusted effect of BMI category on graft and patient survival. Average accumulated costs of care according to BMI were calculated using a modification of the Kaplan-Meier methodology for continuous data [27] utilized in similar analyses [23, 24, 28-30]. Alpha was set at 5% for all significance tests. Data management and analyses were performed using SAS® v.9.2 (SAS Institute, Cary, NC). Tables and figures were created using Microsoft Office Excel® 2007 (Microsoft Corporation, Redmond, WA).

Results

767 privately-insured adult renal transplant recipients were identified by the selection criteria. Among the eligible subjects, the distribution of transplant BMI was 23 underweight (3.0%), 267 normal (34.8%), 264 overweight (34.4%), 161 obese (19.7%), 51 morbidly obese (6.6%), and 11 extremely morbidly obese (1.4%). Recipient, donor, and transplant characteristics by BMI category are summarized in (Table 1). A significant p-value indicates that the variable of interest was not independent by BMI category.

  Underweight Normal Weight Overweight Obese Morbidly Obese Ext. Mor. Obese  
Variable N % N % N % N % N % N % p-value
Recipient Characteristics                          
Gender                         <.001
Female 18 78.26 126 47.19 89 33.71 62 41.06 20 39.22 3 27.27  
Race                         <.001†
African American 5 21.74 38 14.23 53 20.08 30 19.87 14 27.45 4 36.36  
Other 3 13.04 37 13.86 43 16.29 15 9.93 3 5.88 1 9.09  
White 15 65.22 192 71.91 168 63.64 106 70.20 34 66.67 6 54.55  
Ethnicity                         0.388†
Hispanic 1 4.35 19 7.12 30 11.36 12 7.95 2 3.92 0 0.00  
Age (years)                         0.007†
18 - 30 2 8.70 25 9.36 17 6.44 5 3.31 1 1.96 0 0.00  
31 - 44 12 52.17 113 42.32 83 31.44 41 27.15 14 27.45 4 36.36  
45 - 59 7 30.43 92 34.46 114 43.18 79 52.32 25 49.02 6 54.55  
> 60 2 8.70 37 13.86 50 18.94 26 17.22 11 21.57 1 9.09  
Primary cause of ESRD                         0.727†
Diabetes mellitus 6 26.09 115 43.07 107 40.53 56 37.09 19 37.25 4 36.36  
Glomerulonephritis 8 34.78 50 18.73 53 20.08 31 20.53 11 21.57 1 9.09  
PKD                3 13.04 24 8.99 30 11.36 17 11.26 3 5.88 2 18.18  
Hypertension       3 13.04 36 13.48 44 16.67 25 16.56 6 11.76 3 27.27  
Unknown                      0 0.00 1 0.37 3 1.14 1 0.66 0 0.00 0 0.00  
Other                           3 13.04 41 15.36 27 10.23 21 13.91 12 23.53 1 9.09  
Pre-Transplant Dialysis Duration                         0.446†
None (pre-emptive) 3 13.04 68 25.47 52 19.70 25 16.56 8 15.69 2 18.18  
> 0   - 12 months 5 21.74 51 19.10 52 19.70 29 19.21 7 13.73 1 9.09  
> 12 - 24 months 4 17.39 60 22.47 62 23.48 28 18.54 9 17.65 3 27.27  
> 25 - 60 months 7 30.43 66 24.72 77 29.17 51 33.77 22 43.14 5 45.45  
> 60 months 4 17.39 22 8.24 21 7.95 18 11.92 5 9.80 0 0.00  
Diabetes 7 30.43 120 44.94 125 47.35 64 42.38 20 39.22 6 54.55 0.546
PVD 0 0.00 7 2.62 10 3.79 7 4.64 1 1.96 0 0.00 0.847†
Donor Characteristics                          
Gender                         0.331
Female 11 47.83 98 36.70 116 43.94 65 43.05 17 33.33 6 54.55  
Race                         0.182†
African American 6 26.09 21 7.87 23 8.71 16 10.60 5 9.80 0 0.00  
White 5 21.74 32 11.99 37 14.02 21 13.91 8 15.69 3 27.27  
Other 12 52.17 214 80.15 204 77.27 114 75.50 38 74.51 8 72.73  
Age (years)                         0.051†
≤ 18 4 17.39 50 18.73 41 15.53 11 7.28 8 15.69 0 0.00  
19 - 30 6 26.09 81 30.34 62 23.48 44 29.14 11 21.57 2 18.18  
31 - 44 7 30.43 72 26.97 80 30.30 42 27.81 12 23.53 4 36.36  
45 - 59 6 26.09 57 21.35 68 25.76 48 31.79 15 29.41 3 27.27  
≥ 60 0 0.00 7 2.62 13 4.92 6 3.97 5 9.80 2 18.18  
Missing                          
BMI category (kg/m2)                         0.720
≥ 10 to < 25 11 47.83 147 55.06 132 50.00 73 48.34 24 47.06 3 27.27  
≥ 25 to < 30 7 30.43 77 28.84 80 30.30 45 29.80 18 35.29 4 36.36  
≥ 30 5 21.74 43 16.10 52 19.70 33 21.85 9 17.65 4 36.36  
Death due to stroke 4 17.39 94 35.21 109 41.29 60 39.74 20 39.22 6 54.55 0.173
Terminal Creatinine ≥ 1.5 3 13.04 27 10.11 34 12.88 18 11.92 8 15.69 2 18.18 0.825
Hypertension history 4 17.39 47 17.60 56 21.21 31 20.53 9 17.65 2 18.18 0.925
Diabetes 0 0.00 4 1.50 9 3.41 7 4.64 3 5.88 0 0.00 0.276†
CMV Status                         0.619†
Sero-positive 13 0.00 156 1.50 153 0.76 102 0.66 33 0.00 5 0.00  
Missing 0 56.52 4 58.43 2 57.95 1 67.55 0 64.71 0 45.45  
Transplant Factors                          
Donor type                         0.028†
SCD 22 95.65 238 89.14 220 83.33 128 84.77 40 78.43 9 81.82  
ECD 1 4.35 16 5.99 35 13.26 10 6.62 8 15.69 2 18.18  
DCD 0 0.00 13 4.87 9 3.41 13 8.61 3 5.88 0 0.00  
Peak PRA                         0.331†
0-10% 16 69.57 215 80.52 209 79.17 112 74.17 42 82.35 10 90.91  
11-30% 1 4.35 22 8.24 21 7.95 16 10.60 5 9.80 1 9.09  
>30% 4 17.39 27 10.11 31 11.74 20 13.25 2 3.92 0 0.00  
Unknown 2 8.70 3 1.12 3 1.14 3 1.99 2 3.92 0 0.00  
CMV sero-pairing                         0.668†
Unknown                   1 4.35 23 8.61 17 6.44 7 4.64 2 3.92 1 9.09  
Donor - / Recipient -   5 21.74 48 17.98 43 16.29 19 12.58 6 11.76 3 27.27  
Donor - / Recipient +   5 21.74 49 18.35 61 23.11 28 18.54 12 23.53 2 18.18  
Donor + / Recipient -  5 21.74 72 26.97 66 25.00 35 23.18 15 29.41 3 27.27  
Donor + / Recipient + 7 30.43 75 28.09 77 29.17 62 41.06 16 31.37 2 18.18  
HLA Mismatches                         0.884†
0 HLA mismatches 1 4.35 46 17.23 38 14.39 31 20.53 8 15.69 0 0.00  
1 HLA mismatches 0 0.00 4 1.50 4 1.52 1 0.66 0 0.00 0 0.00  
2 HLA mismatches 0 0.00 19 7.12 16 6.06 8 5.30 2 3.92 0 0.00  
3 HLA mismatches 8 34.78 38 14.23 41 15.53 18 11.92 7 13.73 3 27.27  
4 HLA mismatches 7 30.43 58 21.72 54 20.45 36 23.84 14 27.45 3 27.27  
5 HLA mismatches 5 21.74 69 25.84 81 30.68 40 26.49 14 27.45 4 36.36  
6 HLA mismatches 2 8.70 33 12.36 30 11.36 17 11.26 6 11.76 1 9.09  
Sensitized 3 13.04 23 8.61 22 8.33 11 7.28 1 1.96 0 0.00 0.486†
Cold Ischemia Time                         0.448†
0 to < 15 hours 8 34.78 111 41.57 99 37.50 64 42.38 25 49.02 7 63.64  
15 to < 20 hours 4 17.39 57 21.35 54 20.45 29 19.21 9 17.65 1 9.09  
20 to < 26 hours 3 13.04 32 11.99 36 13.64 23 15.23 10 19.61 0 0.00  
26+ hours 3 13.04 14 5.24 24 9.09 15 9.93 3 5.88 0 0.00  
Unknown 5 21.74 53 19.85 51 19.32 20 13.25 4 7.84 3 27.27  
Year‡                         0.696†
2000 1 2.78 18 50.00 10 27.78 6 16.67 1 2.78 0 0.00  
2001 3 4.41 29 42.65 15 22.06 15 22.06 4 5.88 2 2.94  
2002 5 5.10 32 32.65 37 37.76 18 18.37 5 5.10 1 1.02  
2003 3 2.65 35 30.97 40 35.40 26 23.01 7 6.19 2 1.77  
2004 4 3.39 45 38.14 41 34.75 19 16.10 9 7.63 0 0.00  
2005 3 2.50 41 34.17 51 42.50 15 12.50 7 5.83 3 2.50  
2006 3 2.03 46 31.08 48 32.43 37 25.00 12 8.11 2 1.35  
2007 1 1.52 21 31.82 22 33.33 15 22.73 6 9.09 1 1.52  

Table 1: Summary statistics of variables of interest by BMI category for privately-insured transplant recipients 2000-2007 (N=767).

Female transplant recipients differed statistically by BMI and accounted for over three quarters of the underweight BMI category. Racial composition illustrated African American recipients generally increased away from normal weight. Age group was statistically associated with BMI. The majority of underweight recipients were comprised of 31- to 44-year olds with a shift to 45-to 59-year olds in the overweight through extremely morbidly obese categories. Diabetes mellitus was the most prevalent cause of ESRD for those with a BMI in the normal through morbidly obese range. Amongst the underweight group, glomerulonephritis was the most common cause of ESRD. The proportion of pre-emptive transplantations, those with no pretransplant dialysis, was largest for normal BMI recipients. Diabetes at time of transplant was less common for underweight recipients. PVD was rare across all BMI groups. Distribution of BMI category approached statistical significance for donor age. Underweight and normal BMI recipients received more of the SCD organs than other BMI groups. Transplant prevalence by BMI category over time is displayed graphically in (Figure 1).

nephrology-therapeutics-Transplant

Figure 1: Privately-Insured Kidney Transplant Recipient Body Mass Index Category 2000 – 2007. Description: The proportion of transplant recipients with elevated BMI increased, while the normal BMI group decreased, during the study period. This trend is reflected in the general US population over the same time period.

Secondary outcomes of interest by BMI category are displayed in (Figure 2). The prevalence of both DGF and graft failure escalate away from normal BMI category. Though graft failure is approaching statistical significance (p = 0.052), only DGF has a significant association with BMI (p = 0.024). Patient death is lowest for overweight and obese recipients. Length of transplant hospitalization was longest for extremely morbidly obese recipients and differed statistically from each BMI level except underweight. No additional comparisons of length of transplant hospitalization by BMI group were statistically significant. Of the secondary outcomes, only DGF is significantly different by recipient BMI category distribution.

nephrology-therapeutics-Outcomes

Figure 2: Privately-Insured Kidney Transplant Recipient Secondary Outcomes by BMI Category. Description: The prevalence of both DGF and graft failure increased for underweight and elevated BMI categories. Patient death is lowest for overweight and obese recipients. Length of transplant hospitalization was longest for extremely morbidly obese recipients and differed statistically from each BMI level except underweight. Of these secondary outcomes, only DGF is significantly different by recipient BMI category distribution.

Average accumulated costs associated with transplant recipient are summarized by BMI categories as well as recipient, donor, and transplant characteristics during the transplant hospitalization and each of the three follow-up periods in (Table 2). When controlling for study covariates, none of the BMI categories were significantly different compared to normal BMI recipients during the transplant hospitalization or any of the yearly follow-up periods.

Variable Transplant Hospitalization 1-year posttransplant 2-years posttransplant 3-years posttransplant
Base Cost 70070 * -28380   -31799   37576  
BMI Category                
Underweight -8540   5596   3730   43801  
Normal Reference Reference Reference Reference
Overweight -12870   7826   4637   -10162  
Obese -12905   -3617   5642   33218  
Morbidly Obese -19996   -3474   20418   55592  
Extremely Morbidly Obese -20175   40702   22776   -34014  
Recipient Characteristics                
Gender                
Female 26497 ** 2399   -3035   -8265  
Race                
African American -10098   -9595   -4070   3148  
Other -15977   -16584   3978   -1857  
White Reference Reference Reference Reference
Ethnicity                
Hispanic 19276   22279   10252   44235  
Age (years)                
18 - 30 Reference Reference Reference Reference
31 - 44 -7828   13417   11734   6  
45 - 59 -16835   17260   27629   21223  
> 60 -14957   14268   42366 * 59930  
Primary cause of ESRD                
Diabetes mellitus         3121   25316 * 26713   25959  
Glomerulonephritis -6184   -7223   7426   16076  
PKD                -7337   -1802   -1562   -13481  
Hypertension       -12870   -6970   2356   -14428  
Unknown                      -45876   -20190   25560   44470  
Other   Reference Reference Reference Reference
Pre-Transplant Dialysis Duration                
None (pre-emptive) Reference Reference Reference Reference
0-12 months 12652   12901   -2024   -16203  
13-24 months 6231   7864   -12766   -21853  
25-60 months -18621   -16540 * -13491   -4378  
More than 60 months -51686 ** -9010   -6444   -27753  
Diabetes 15439   -11413   4493   371  
PVD -6220   -14875   -23073   16680  
Donor Characteristics                
Gender                
Female 8272   14402 * 9032   465  
Race                
African American -18107   8120   31607 * 21420  
Other -6863   -4212   -7077   -12514  
White Reference Reference Reference Reference
Age (years)                
≤ 18 6518   13501   10236   1749  
19 - 30 Reference Reference Reference Reference
31 - 44 -14405   1579   10937   -7917  
45 - 59 -20417   -5060   16748   928  
≥ 60 -35394   16802   906   -68840  
BMI category (kg/m2)                
≥ 10 to < 25 Reference Reference Reference Reference
≥ 25 to < 30 18357 * 7544   12205   -5331  
≥ 30 -4106   8494   19060   24686  
Death due to stroke 9548   15654 * -1515   -10131  
Terminal Creatinine ≥ 1.5 -8113   -11567   -18094   -43371  
Hypertension history 5024   8208   -2891   -13125  
Diabetes -2332   -2561   -29683   -30886  
CMV sero-positive -21471   -33716 * 14793   -6232  
Transplant Factors                
Donor type                
SCD Reference Reference Reference Reference
ECD 30973   -2688   -15660   54694  
DCD -35675 * 224   1002   5077  
Peak PRA %                
0-10% Reference Reference Reference Reference
11-30% 9475   -3482   -8659   -10004  
>30% -8005   1138   8841   -7005  
Unknown 8640   -9641   -3474   -56647  
CMV sero-pairing                
Unknown                   23107   15345   -14562   18459  
Donor - / Recipient -   Reference Reference Reference Reference
Donor - / Recipient +  37938   47374 ** -5895   40650  
Donor + / Recipient -  12872   8342   -1149   23114  
Donor + / Recipient + 28850   39048 * -25844   18631  
HLA Mismatches                
0 HLA mismatches Reference Reference Reference Reference
1 HLA mismatches 948   -3249   53996   34729  
2 HLA mismatches -17763   2325   -10494   -45940  
3 HLA mismatches -1603   3625   -5230   -35855  
4 HLA mismatches 10476   8458   -9789   -13697  
5 HLA mismatches 3610   19038 * -7846   -29259  
6 HLA mismatches -12607   15003   -2082   -23253  
Sensitized 1909   10080   25081   12253  
Cold Ischemia Time                
0 to < 15 hours Reference Reference Reference Reference
15 to < 20 hours 4044   -4373   -4315   7743  
20 to < 26 hours -18178   5433   4093   1000  
26+ hours -16712   7057   7845   5421  
Unknown -34181 ** 15804 * 16992   17583  
Year                
2000 Reference Reference Reference Reference
2001 39772   -10997   68370 *** -50162 *
2002 41913 * 40669 *** 18727   -19618  
2003 47434 * 97   6065   -41465 *
2004 41061 * 2885   17926   -14581  
2005 72463 *** -721   4239      
2006 73810 *** 9535          
2007 72630 **            
Length of Stay 4150   1304 * 1403   1571  

Table 2: Total accumulated cost (in dollars) at transplant hospitalization as well as one, two, and three year for privately-insured transplant recipients 2000-2007 (N=767).

A summary of Cox proportional hazard models is reported in (Table 3). A full regression model of graft failure using Cox proportional hazard analysis showed a significant adjusted increase in effect for underweight, overweight, obese, and morbidly obese recipients. A stepwise Cox model on graft failure, with forced entry for the BMI categories, also had significant adjusted increase in effects for underweight, overweight, obese, and morbidly obese recipients. No significant adjusted effect was found for patient survival by BMI category using Cox proportional hazards analysis.

  Graft Survival Patient Survival
Variable Full Stepwise Full Stepwise
BMI Category                
Underweight 5.383 * 6.159 ** 10.168   1.565  
Normal Reference Reference Reference Reference
Overweight 2.283 * 2.578 ** 1.002   0.942  
Obese 2.681 * 2.846 ** 0.393   0.671  
Morbidly Obese 4.279 * 4.351 ** 2.559   1.762  
Extremely Morbidly Obese 3.434   2.754   3.229   1.551  
Recipient Characteristics                
Gender                
Female 0.812       0.520      
Race                
African American 1.385       0.582      
Other 0.000       0.000      
White Reference     Reference    
Ethnicity                
Hispanic 3.026E+06       1.726E+07      
Age (years)                
18 - 30 Reference     Reference    
31 - 44 2.993       9.893E+07      
45 - 59 2.459       5.784E+07      
> 60 3.613       5.141E+07      
Primary cause of ESRD                
Diabetes mellitus         2.227       47.176      
Glomerulonephritis 0.779       1.004      
PKD                1.798       4.130      
Hypertension       1.172       1.623      
Unknown                      20.783 *     0.000      
Other                            Reference     Reference    
Pre-Transplant Dialysis Duration                
None (pre-emptive)         Reference     Reference    
0-12 months 1.691       14.737 *    
13-24 months 1.906       20.687 *    
25-60 months 1.784       13.530      
More than 60 months 2.325       31.123 *    
Diabetes 0.402       0.028      
PVD 0.878       1.226      
Donor Characteristics                
Gender                
Female 1.855       1.069      
Race                
African American 0.965       0.088      
Other 0.652       0.229      
White                          Reference     Reference    
Age (years)                
≤ 18 2.052       0.915      
19 - 30 Reference Reference Reference Reference
31 - 44 0.571   0.482 * 0.363      
45 - 59 1.336       1.291      
≥ 60 0.694       0.797   4.984 **
BMI category (kg/m2)                
≥ 10 to < 25            Reference     Reference    
≥ 25 to < 30 0.751       0.713      
≥ 30 0.583       0.345      
Death due to stroke 2.405 * 2.716 *** 4.714      
Terminal Creatinine ≥ 1.5 1.196       4.134      
Hypertension history 0.806       0.275      
Diabetes 1.864       32.789      
CMV sero-positive 4.087E+05       2.723E+06      
Transplant Factors                
Donor type                
SCD Reference     Reference    
ECD 1.475       1.622      
DCD 0.549       0.265      
Peak PRA %                
0-10% Reference            
11-30% 0.531       0.000      
>30% 0.298       0.000      
Unknown 0.404       0.000      
CMV sero-pairing                
Unknown                   0.000       0.000      
Donor - / Recipient -   Reference Reference Reference Reference
Donor - / Recipient +  0.000   1.949 * 0.000      
Donor + / Recipient -  0.673       1.901      
Donor + / Recipient + 0.000       0.000      
HLA Mismatches                
0 HLA mismatches Reference Reference Reference Reference
1 HLA mismatches 7.395   5.344 * 0.010      
2 HLA mismatches 0.000       0.076      
3 HLA mismatches 1.925       2.253E+07      
4 HLA mismatches 1.387       5.460E+06      
5 HLA mismatches 1.880       1.660E+07      
6 HLA mismatches 3.451       9.818E+07   3.204 *
Sensitized 16.315 * 4.564 *** 1.445E+09   7.116 ***
Cold Ischemia Time                
0 to < 15 hours Reference     Reference    
15 to < 20 hours 1.029       0.251      
20 to < 26 hours 0.888       0.154      
26+ hours 1.838       0.000      
Unknown 0.730       0.313      
Year                
2000 Reference     Reference    
2001 1.022       0.719      
2002 0.719       0.219      
2003 0.553       0.026      
2004 0.688       0.074      
2005 0.429       0.555      
2006 1.352       1.764      
2007 0.000       0.000      
Length of Stay 1.128 *** 1.105 *** 1.118 * 1.085 *

Table 3: Cox proportional hazards full and stepwise models for graft and patient survival of privately-insured transplant recipients 2000-2007 (N=767).

Discussion

This study analyzed the impact of BMI on outcomes and cost of care for privately-insured adult kidney transplant recipient between 2000 and 2007 during transplant hospitalization and at one-, two-, and three-years following transplant. We observed that costs of care do not differ statistically by recipient BMI following transplantation when adjusting for numerous patient, donor, and transplant covariates. We also observed that non-normal BMI recipients, except the extremely morbidly obese, have significantly increased risks for graft failure following transplantation.

The increase in prevalence of obesity in the United States is reflected in the swell of transplant recipients with elevated BMI from 2000 to 2007 (Figure 1) [10]. The dramatic shift and trajectory should be alarming to patients, insurance providers, and transplant centers alike. As the challenge of finding quality organs and healthy kidney recipients escalates, attention on modifiable risk-factors, like BMI, should an integral part of the pre-transplant evaluation system.

Normal BMI recipients had a pre-emptive transplant, thus bypassing dialysis, more often than non-normal groups. As less than ideal candidates, non-normal BMI recipients utilized dialysis between two and five years more often than normal BMI recipients. While the study limits BMI measured at time of transplant, this finding suggests that recipients may have sustained their BMI through candidacy.

Non-normal BMI recipients did not fare well in the secondary outcome measures. DGF was not independent of BMI group (p = 0.024). The relative percentage of DGF escalated considerably away from normal BMI. The proportion of DGF was smallest for normal BMI recipients (11.99%) and swelled steadily as BMI increased to extremely morbidly obese (36.36%). Even underweight recipients had an increased rate of DGF (13.04%). The proportion of graft failure was increased for non-normal BMI recipients, though the difference was slightly out of range for statistical significance (p = 0.052). The percentage of deceased recipients was lowest for overweight (2.65%) and obese (2.65%) recipient. Patient survival was not statistically significant by BMI group. Length of hospitalization differed statistically by BMI (p < 0.001). Overweight recipients had the shortest average length of transplant hospitalization stay (7.93) while extremely morbidly obese recipients had the longest average stay (13.27 days).

Kidney transplantation rates for normal BMI recipients have dramatically shifted from 2000 to 2007 towards overweight and obese recipients. As this analysis has shown, increased costs and inferior outcomes are associated with unfavorable BMI at time of transplantation. While no differences in adjusted cost were detected, the increased risks and inferior outcomes associated with unfavorable BMI at time of transplantation provide ample evidence for policymakers to encourage transplant candidates to obtain a normal BMI by the time of transplantation.

Limitations

This study has several limitations. Our analysis was limited to the quality and availability of the data included in the registry. Despite utilizing elements related to costs and clinical outcomes found in prior studies [23,31], other sources of cost or variation may be absent. Though inexpensive and easy to calculate, BMI may not be the best measure of body composition [32-35]. The cross-sectional assessment of BMI does not allow for dynamic examination reported in previous research [36]. Finally, BMI measurement is cross-sectional at time of transplant thereby limiting the potential for fluctuation of BMI before and after transplantation.

Implications

There are a number of implications as a result of this analysis. Transplant centers and insurance companies may consider directing funds towards weight management programs for transplant candidates as a means of preventing posttransplantation weight gain [37] and reducing costs associated with follow-up care. Using primary data collection might provide a more accurate assessment of costs and risks associated with kidney transplant recipient BMI by using factors not available in this retrospective study. Prospective studies might consider more in-depth cost variables as well as more representative or precise measures of body composition, such as waist-to-hip ratio or body-fat percentage [32]. Future prospective studies might examine the impact of bariatric surgery as a tool for improving posttransplant outcomes and costs. A previous retrospective analysis showed that significant weight loss can be obtained in the ESRD and kidney transplant population undergoing bariatric surgery, although not without risk [38]. Replicating this analysis using recipients with public insurance, or with different graft transplantation, might produce distinctive or confirmatory results. Future studies should obtain body composition measures at multiple points in time to assess stability and change as a result of transplantation. Finally, the results from this analysis may also be used to determine whether the well-accepted survival benefit of kidney transplantation over dialysis remains cost-effective for each BMI category.

Conclusion

We found that privately-insured kidney transplant recipients significantly varied by BMI category in posttransplant outcomes but not costs. The growing demand for transplant recipients with non-normal BMI is at risk for greater healthcare costs and adverse health outcomes following transplant. To reduce preventable costs to the healthcare system and improve posttransplant outcomes, resources should be invested into developing methods to help transplant candidates obtain a normal BMI by the time of transplantation.

Acknowledgements

Krista L. Lentine is supported by a grant from the National Institute of Diabetes Digestive and Kidney Diseases (K08-0730306).

References

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