EXPERIMENTAL AND CLINICAL TRANSPLANTATION

Objectives: As the demand for kidney transplant allografts has increased, many centers are expanding the upper limit of acceptable body mass index for kidney donors. However, obesity is a risk factor for developing renal disease. Our goal was to quantify body mass index trends in donor nephrectomy patients and to institute nutrition counseling to promote sustainable weight loss to reduce the risk of metabolic syndrome-derived renal dysfunction.

Materials and Methods: Ninety patients who underwent donor nephrectomy between 2007 and 2012 consented to having height and weight data collected at multiple time points. After data collection, each patient underwent a standardized nutrition counseling session. One year later, body mass index was reassessed.

Results: Preoperatively, 52% of the patients were overweight or obese. The percentage of overweight and obese patients remained stable for 2 years after surgery. However, at 3, 4, and 5 years after surgery, these rates increased to 59%, 69%, and 91%. Each patient was counseled about obesity-related comorbidities and provided information about lifestyle modification. One year later, 94% of previously overweight patients and 82% of previously obese patients had a decrease in mean body mass index from 27.2 ± 4.0 kg/m² to 25.1 ± 3.6 kg/m².

Conclusions: Living-donor nephrectomy patients are at risk of developing obesity, similar to the adult population. Nutrition counseling may be beneficial to help normalize body mass index in patients who have become overweight or obese to potentially prevent obesity-related comorbidities. All patients were evaluated by a nutrition specialist after surgery to review our donor nephrectomy nutrition brochure. Body mass index monitoring and primary care follow-up appear to be appropriate surveillance methods.

Key words : Kidney donation, Laparoscopic living-donor nephrectomy, Nutrition

Obesity is an epidemic global health problem that continues to grow at an alarming rate as the population ages. Since 1980, the number of obese individuals has doubled worldwide. As of 2014, there were more than 1.9 billion overweight adults, 600 million of which were obese.^1,2 Obesity is associated with multiple medical conditions, including cardiovascular disease, diabetes, several types of malignancy, and renal disease.^3-6 Despite community efforts both domestically and abroad to counsel patients regarding weight management through exercise and healthy eating, the rates of obesity continue to increase. This is of particular concern to physicians who treat obese patients, as many have renal impairment as a direct consequence of metabolic complications from obesity.

In recent years, approximately 6000 people have undergone living-donor nephrectomy per year for kidney transplant to help family members, friends, and even strangers in the United States.⁷ Previous research had demonstrated that individuals who donate a kidney have similar or better outcomes than the general public in terms of end-stage renal disease and overall survival.^8-11 These findings were attributed to the fact that living-donor nephrectomy patients are thoroughly screened before surgery and tend to be healthier than their age-matched peers. However, laparoscopic living-donor nephrectomy surgery is not without risks and long-term consequences. Potential living kidney donors are screened to ensure satisfactory renal function, appropriate psychologic demeanor, and adequate general health before proceeding with living-donor nephrectomy.¹² In addition, given the clear association between obesity and end-stage renal disease, particular attention is paid to the body mass index (BMI) of each living-donor nephrectomy patient in the pre- and postoperative setting, as these patients will rely on a solitary kidney for the remainder of their lives. These findings have highlighted the need for improved understanding about the long-term health outcomes of patients who undergo living-donor nephrectomy.

Although there is variability among centers regarding the maximum BMI that is permitted for a patient to donate a kidney, most kidney transplant programs have an absolute cutoff of a BMI of 35 kg/m², and many will not consider a patient for donation until the BMI is below 30 kg/m².¹³ However, with increased demand for renal allografts for transplants, many centers are expanding donation criteria to include higher percentages of obese kidney donors.¹⁴ It has been shown that laparoscopic donor nephrectomy is more technically challenging in obese patients; however, short-term health-related outcomes for obese kidney donors have been similar to those of normal weight adults.^15,16 Much attention is given to the preoperative workup of the patient, and, postoperatively, patient data are transmitted to the United Network for Organ Sharing (UNOS) organization to record and assess vital signs and height/weight for 1 to 2 years. However, after this brief time period, patient information is no longer transmitted to UNOS. Patients must then rely solely on their primary care providers to monitor blood pressure, BMI, and diet and exercise plans, as well as urine and blood studies to screen for potential risk factors for renal deterioration. Because most living-donor nephrectomy patients are of normal BMI and in good health preoperatively, we would not expect to see significant changes in BMI within the 2-year window tracked by UNOS. However, previous research has shown an increase in BMI at that 2-year mark.17 Our study was designed to follow living-donor nephrectomy patients past 2 years to (1) assess trends in BMI, (2) track changes in rates of obesity in this unique patient population, (3) implement nutrition and lifestyle guidelines based on these findings, and (4) design an appropriate follow-up interval and method to monitor BMI to ensure the continued health of these patients. First, we hypothesized that living-donor nephrectomy patients would have gradually increasing rates of obesity after the 2 years of surveillance by UNOS, similar to the characteristic obesity trends of the American public. Second, we hypothesized that, if living-donor nephrectomy patients did have increased rates of obesity at long-term follow-up, they would positively respond to nutrition counseling and reduce BMI given the morbidity associated with metabolic complications from obesity.

Materials and Methods

Cedars-Sinai Medical Center in Los Angeles, California, is a comprehensive multiorgan transplant center. From 2007 to 2012, 332 living-donor nephrectomies were performed with a coordinated surgical effort between the transplant, vascular, and urologic surgery teams. All patients were counseled preoperatively regarding the importance of weight management with diet and exercise and obesity-related medical complications. All surgeries were performed laparoscopically utilizing three 12-mm trochars and an 8-cm Pfannenstiel incision for kidney removal. After Institutional Review Board approval (number Pro00031212; approval date 02/06/2013), 90 patients who underwent living-donor nephrectomy consented and agreed to have their height and weight recorded on a yearly basis for the purpose of calculating BMI. All research involving human subjects was approved by the ethics committee of the institution before the study began, and the protocols conformed to the ethical guidelines of the 1975 Helsinki Declaration. Each patient reported serial height and weight information as measured on a calibrated scale on the same day of the week in the nude immediately after waking, voiding, and defecating to control for changes by added articles of clothing, time of day, fasting status, urine in the bladder, or stool in the colon.^18,19

Over a period of 1 year, each patient was contacted 2 times to assess height and weight (at time of first contact and 1 year after first contact). In addition, each patient was asked about diet, activity level, exercise, and fitness goals. Real-time feedback was provided about healthy eating, exercise, and weight management utilizing nutrition and fitness information from the published literature.^20,21 Again, the morbidity of obesity-related medical complications, including but not limited to renal failure, hypertension, diabetes, metabolic syndrome, neuropathy, cerebrovascular disease, and cardiovascular disease, were discussed in depth. Each patient demonstrated understanding, and all questions were answered.

Point of initial contact ranged from 1 to 5 years after the surgical procedure, depending on the original date of surgery. The following BMI definitions were applied: underweight (BMI of < 18.5 kg/m²), normal weight (BMI of 18.5-24.9 kg/m²), overweight (BMI of 25-29.9 kg/m²), and obese (BMI of 30-35 kg/m²). During data abstraction, all protected health information was immediately deidentified and kept under lock and key in a secure office. All electronic information was secured on an Institutional Review Board-approved device under password protection and, when not in use, under lock and key.

Statistical analyses were performed using Microsoft Excel version 12.2.3. We used t test to determine significance; standard deviation is provided where applicable.

Preoperative assessment of body mass index
The baseline preoperative characteristics of the 90 patients are presented in Table 1. Mean patient age was 46.1 years (range, 25-63 y), and 66/90 patients (73%) were female. The mean BMI was 25.5 ± 3.9 kg/m2 (range, 18.6-33.5 kg/m2). Of the total study patients, 43 (48%) were classified as normal weight, 34 (38%) as overweight, and 13 (14%) as obese. Most patients underwent donor nephrectomy of the left kidney (85/90; 94%).

Postoperative body mass index (initial contact)
The point of initial contact after nephrectomy ranged from 1 to 5 years postoperatively, depending on the date of the original surgery. Body mass index information was collected from each patient and compared with preoperative values. At the time of initial contact postoperatively, the mean BMI had risen to 27.2 ± 4.0 kg/m2 (range, 19.4-35.5 kg/m2), and 40/90 patients (44%) were classified as normal weight, 33/90 patients (37%) as overweight, and 17/90 patients (19%) as obese. Of the 34 patients who were overweight preoperatively, 14 patients (41%) had a decrease in BMI and 20 patients (59%) had an increase in BMI at time of first contact. Of the 13 patients who were obese preoperatively, 6 patients (46%) had a decrease in BMI and 7 patients (54%) had an increase in BMI at time of initial contact. At the close of the initial contact conversation, each patient was counseled and provided information about healthy eating, fitness, and weight loss in the context of renal disease from obesity and diabetes. Changes in the composition of overweight and obese patients as a function of years from surgery are displayed in Figure 1. We observed a direct correlation between the numbers of years from surgery and the percent increase of overweight and obese patients. The percentage of overweight and obese patients remained stable for the first 2 years after surgery. However, at 3, 4, and 5 years postoperatively, these figures increased to 59%, 69%, and 91%, with all statistically significant (P = .002).

Postoperative body mass index (1 year after initial contact)
One year after the initial encounter, each patient was contacted to reassess BMI and to address nutrition and fitness progress. Information on BMI was collected from each patient to compare with preoperative and initial contact values. At this time point, the mean BMI was 25.1 ± 3.6 kg/m² (range, 18.4-32.9 kg/m²), with an average decrease of 2.1 BMI points from the previous encounter. Of the 91 patients, 51 patients (57%) were now classified as normal weight, 28 patients (31%) as overweight, and 11 patients (12%) as obese. The relative BMI distribution was similar to that from the time of initial contact 1 year earlier. However, of patients who were overweight at the initial contact (n = 33), 31 patients (94%) had a decrease in BMI. Of patients who were obese at the initial contact (n = 17), 14 (82%) had a decrease in BMI, a marked change from 1 year previously (Table 2).

We have shown that living-donor nephrectomy patients had a significant increase in BMI composition toward overweight and obese when monitored after the traditional 2-year surveillance window after surgery. This can likely be explained because of the tapering of rigorous follow-up and the fact that there are no functional or physical limitations after laparoscopic living-donor nephrectomy surgery once the incisions have healed. This patient population is similar to the normal adult population and, therefore, is similarly at risk for the development of obesity. What differentiates the living-donor nephrectomy patient population is functional renal reserve. There is a clear association between increasing age and obesity as previously described, and it is our goal to protect the living-donor nephrectomy patients from metabolic syndrome-derived renal dysfunction, thus avoiding any future need to receive dialysis or a kidney transplant themselves.

Our study also demonstrates that a single health maintenance counseling session with a physician may have helped to facilitate a significant weight loss trend that was independent of the postoperative time frame (range, 1-5 y). Successfully losing weight is a multifactorial process affected by many elements, such as family history, personal health history, internal drive, and social support. It is important to note that the donor nephrectomy patient population is a highly selective group of motivated individuals who may have responded to nutrition counseling more aggressively than age-matched peers given the intentional selection bias. Regardless, the finding is impressive. Mean BMI decreased from 27.2 ± 4.0 kg/m² to 25.1 ± 3.6 kg/m² at 1 year after nutrition counseling. Although this change only bordered on statistical significance (P = .09), given the broad range of starting BMIs, it has dramatic clinical significance, as there was an average drop by 2.1 BMI points and a break in the previous trend. To place this change in context of real weight loss, a man that is 5 feet 9 inches (1.75 meters) tall and 170 lb (77 kg) would need to lose 14 lb (6.4 kg) to have a 2.1 BMI point decrease, assuming no change in height.

This was a prospective observational study of a specific group who had previously undergone living-donor nephrectomy, and all individuals received nutrition counseling. There was no randomized control arm in the study population, as it was not within the original scope of the study. Each patient served as his or her own control to demonstrate a BMI trend before and after implementation of nutrition counseling. There is a great deal of literature about the response to nutrition and fitness counseling for at-risk groups. Weight loss management and counseling programs have been validated in obese patients with a multitude of medical conditions and socioeconomic backgrounds.^22-25 In fact, weight loss was one of the only factors that has been shown to help reduce the rate of medically preventable renal failure.²⁶ Our study, the first of its kind in a donor nephrectomy population, supports the previous findings in other groups that nutrition and fitness counseling can be important factors in achieving weight loss.

As a result of these findings, all of our donor nephrectomy patients are seen and evaluated immediately after surgery in the hospital by a nutrition specialist. A detailed information brochure was created specifically for donor nephrectomy patients to address the nutrition and fitness goals as a result of the findings of this study. Additionally, nutrition and fitness are discussed at length during subsequent surgical office visits using the brochure as a guide. More than half of living-donor nephrectomy patients who participated in this study were overweight or obese on the day of surgery. This highlights the importance of nutrition and exercise counseling and BMI optimization even before the anticipated surgery date. Given the morbidity of end-stage renal disease from obesity-related complications and well-documented increasing trends in BMI over time, nutrition counseling is of the utmost importance in the pre- and postoperative evaluations of donor nephrectomy patients.

Although it has not been adequately studied, obesity leading to metabolic derangements and end-stage renal disease may possibly affect living-donor nephrectomy patients at an increased rate relative to the normal adult population, given their decreased renal reserve. Several small retrospective studies have shown that there is no increased risk of deterioration in renal function in obese patients who donate a kidney during the first 5 years after surgery.^27-29 However, the follow-up duration was short, and these studies all concluded that overweight and obese kidney donors need intensive preoperative education and postoperative health maintenance. On the other hand, a recent cohort study of over 95 000 patients who underwent living-donor nephrectomy for kidney transplant demonstrated an increased risk of end-stage renal disease over a median 7.6 years versus that shown in matched healthy nondonors.³⁰ The magnitude of the absolute risk increase was small but significant. Although this study did not stratify BMI, it suggests that donor nephrectomy patients may be at increased risk of renal deterioration due to decreased renal reserve.

A limitation of this study is important to note. Body mass index (kg/m²) was used to assess obesity in this study. There has been some scrutiny of this unit of measure, with the World Health Organization suggesting that the ratio of visceral fat to subcutaneous fat may be a better measure to define obesity in that the values better correlate with the associated comorbidities.³¹ However, BMI is an inexpensive and efficient measure of obesity and has been validated in the literature and endorsed by the World Health Organization as the preferred screening to assess body habitus and the need for intervention.³² Therefore, we feel confident in our use of BMI to assess trends in obesity.

In conclusion, we have demonstrated that patients who undergo living-donor nephrectomy continue to be at risk of developing obesity, similar to that shown in the normal adult population. Implementation of yearly nutrition and health maintenance counseling for patients who undergo kidney donation may be beneficial to help normalize BMI and prevent the potentially devastating comorbidities associated with obesity. Our study group will continue to monitor changes in BMI trend and provide active and on-going support on a yearly basis. As our patient cohort ages, we will also collect laboratory data to track renal function and monitor for evidence of metabolic syndrome. In addition, all of our patients are now seen and evaluated by a nutrition specialist immediately after surgery to review the important elements from our donor nephrectomy nutrition brochure. Frequent home BMI monitoring in conjunction with yearly follow-up visits with a primary care physician appear to be appropriate methods of surveillance.

Volume: 15 Issue: 5 October 2017

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