Obesity in Living Kidney Donors: Clinical Characteristics and Outcomes in the Era of Laparoscopic Donor Nephrectomy

Julie K. Heimbach; Sandra J. Taler; Mikel Prieto; Fernando G. Cosio; Stephen C. Textor; Yogish C. Kudva; George K. Chow; Michael B. Ishitani; Timothy S. Larson; Mark D. Stegall

Disclosures

American Journal of Transplantation. 2005;5(5):1057-1064. 

In This Article

Discussion

Our results indicate that otherwise healthy Caucasian renal donors whose BMI extends above 30 kg/m2 (classified as obese) and with normal renal function can donate a kidney safely in the short-term. Our selection criteria based upon blood pressure, family history of diabetes and cardiovascular disease led to greater exclusion rates in obese donor candidates. Operative times for laparoscopic donor nephrectomy were longer for obese donors, with higher rates of perioperative complications only in the most obese donors but without difference in LOS. Although considered acceptable, blood pressure, fasting plasma glucose levels and lipid values were higher in donors with BMI ≥ 30 pre-operatively and remained so 6-12 months after nephrectomy. There were no differences in residual renal function or microalbuminuria across BMI groups.

Existing evidence suggests that people who donated kidneys over the past 50 years have not incurred a significant increase in health risks. Late follow-up series of renal donors report a small increased risk of hypertension or proteinuria after renal donation with maintenance of normal renal function.[1,7,8] These reports include primarily donors of normal weight and excellent health. With the increasing success of living donation and the shortage of deceased-donor kidneys, prospective donors are being considered even with isolated medical conditions such as obesity that place them outside what traditionally might be considered ideal donors. We have approached these non-conventional donors using strict selection criteria (absence of albuminuria, normoglycemia, corrected iothalamate clearance > 80 mL/min per 1.73 m2), and a requirement for follow-up (currently a mean of 11 months in this study).

Our findings provide new information on several aspects of the donor process: differences in baseline clinical parameters including cardiovascular risk factors, perioperative course, and measurement of renal function 1 year after donation. We noted higher fasting glucose levels and cholesterol measurements with greater BMI even though values were within the normal range. There was a definite trend to higher blood pressure levels with greater BMI. Technical factors may contribute to elevated readings related to arm size and difficulty with blood pressure cuff fit. Once corrected for donor size (using body surface area), renal function as assessed by iothalamate clearance did not differ across BMI groups.

Most of the surgical literature suggests that obese patients have more perioperative complications and a slower recovery rate compared to non-obese patients. The few studies of perioperative complications in obese living kidney donation suggest that from a surgical perspective, kidney donation is safe. Pesavento et al. showed that 107 obese living kidney donors had similar complications to 116 non-obese donors.[2] However, in that study the group designated obese included individuals with BMI ≥ 27 kg/m2, some of whom would now be classified as only overweight by World Health Organization definition. Reports by others confirm the safety and feasibility of the laparoscopic technique for all kidney donors including those who are obese.[3,5]

In our current study of 553 hand-assisted laparoscopic donor nephrectomies, 172 of whom had a BMI ≥ 30 kg/m2, we found that major surgical complications (conversion to open nephrectomy, re-operations, etc.) were no more common in obese than non-obese donors. Operative time was increased (by a mean of 19 min) and total perioperative complication rate was higher in the highest BMI group compared to BMI < 25. Most of this increase was due to wound complications such as infections and seromas. The overall 9—10% wound complication rate for obese patients is a moderate increase over the 2—4% rate in non-obese donors and should be part of the informed consent given to obese donors.

One of the major demonstrated benefits of minimally invasive surgery is a shortened recovery time. Indeed, in our study the post-operative length-of-stay was similar for obese and non-obese donors. Other data such as return to work or return to previous level of functioning were not collected in this study but would be helpful to assess the differential impact of laparoscopic donor nephrectomy by donor BMI. The current study demonstrates a low procedure-related morbidity and good early recovery in obese donors. While the current study does not provide data comparing open to laparoscopic approaches to donation, it is our opinion that the technique of laparoscopic donor nephrectomy results in reduced morbidity in obese patients and has a positive impact on their perioperative outcomes.

At follow-up 1 year after renal donation, obese donors had comparable levels of residual renal function as demonstrated by iothalamate clearance. Measurements of urinary microalbumin were normal at baseline and did not change following donor nephrectomy. Blood pressure was lower overall at the follow-up visit and stable or lower in individual subgroups. It must be emphasized that while these early data are encouraging, this follow-up must be considered short in these donors who are expected to live for decades.

Long-term follow-up of renal donors is limited. This is especially true regarding obese donors, as obesity has been considered a relative exclusion until recently. Anderson et al. reported a 10- to 20-year follow-up on 105 donors (73% response rate).[1] Of the 100 surviving donors, mean serum creatinine was 1.2 mg/dL and mean 24-h urine protein was 89 mg. Hypertension was present in 19%, defined as blood pressure of 160/95 MmHg or higher. Rates of proteinuria were low (13%), only 3 with levels above 500 mg/24 h. The highest level of proteinuria was seen in an obese donor with progressive weight gain raising the possibility that his obesity may have played a role. Reports by others demonstrate rates of hypertension and proteinuria similar to those of the age-matched general population.[7,8] Torres et al. reported greater weight gains 10 years after donation in renal donors who were already overweight at the time of donation.[9] Weight, age and MAP at donation were predictors of hypertension (160/95 MmHg or on medications) at follow-up. Gracida et al. reported an 80-month follow-up of 628 renal donors, 81 of whom were obese (BMI > 30 kg/m2) at the time of donation. While obese donors showed a trend to higher mean arterial pressure and higher unindexed GFR, there were no significant differences from normal donors.[10]

Perhaps the greatest risk for renal disease in obese donors is the possibility that they may be at greater risk for developing type II diabetes mellitus later in life. Prevalence rates for diabetes (diagnosed and undiagnosed) range from 2.2% in the second and third decades to 19% at age ≥ 60 years.[11] Risk for diabetes increases approximately two-fold in black and Mexican-Americans. BMI is a strong predictor of diabetes risk, as demonstrated in Caucasian, Hispanic and Pima-Indian populations.[12—16] The impact of nephrectomy on the obese individual who subsequently develops diabetes or hypertension is unknown, although hypertension alone in non-obese Caucasian donors rarely leads to renal failure. In long-term (20—37 years) follow-up of 773 living kidney donors, Ramcharan and Matas detected 19 donors who developed diabetes after donation; in six who had follow-up creatinine measurements, only one value was elevated at 2.0 mg/dL and none developed renal failure.[7] We pay special attention to fasting glucose levels in our evaluation and require normal urinary microalbumin excretion (< 30 mg/24 h). This approach is in agreement with the recommendations of the Expert Committee on the Diagnosis and Classification of Diabetes Mellitus that neither hemoglobin A1c nor oral glucose tolerance testing (OGTT) provide more sensitive diagnostic capability, related to lack of standardized methodologies, less reproducibility and greater cost (17,18). We exclude donor candidates with impaired glucose tolerance (≥ 110 mg/dL), for whom OGTT is currently advised. Recent changes in the definition of impaired glucose tolerance (from ≥ 110 mg/dL to ≥ 100 mg/dL) may require stricter limits on donor selection but did not utilize either hemoglobin A1c or OGTT. We depend upon measured renal function by iothalamate clearance rather than calculated GFR and require an iothalamate clearance of greater than 80 mL/min after correction for body surface area to ensure donors have adequate remaining renal function after donor nephrectomy. Family history of diabetes was considered in decision making as reflected by differences in rates between donors accepted and those denied, particularly at the highest levels of BMI ( Table 2 ).

Does obesity by itself constitute an increased risk for developing kidney disease? We believe that the answer to this question is currently unknown. Praga et al. reported that in patients who underwent nephrectomy for medical reasons, proteinuria and/or elevated serum creatinine (mean serum creatinine 3.9 ± 3.2 mg/dL) developed in 92% (12/14) of patients who were obese at the time of nephrectomy compared to 12% of 59 non-obese patients.[19,20] The presence of renal disease and co-morbid conditions at the time of nephrectomy was not presented in detail and may not be applicable to donors in the current study. These findings implicate the combination of obesity and reduced number of functioning nephrons after nephrectomy as a high-risk state for the development of proteinuria and renal failure. Proteinuria has been reported with massive obesity, most commonly caused by focal and segmental glomerulosclerosis (FSGS). Additionally, there are reports of a different renal lesion in obese individuals characterized by glomerulomegaly with fewer lesions of segmental sclerosis and less extensive foot process effacement. This entity termed obesity-related glomerulopathy (ORG), was more commonly identified in a large biopsy series, increasing from 0.2% to 2%, a tenfold increase over 15 years.[21] Parallel increases in obesity over this time suggest that the prevalence of this disease may continue to increase, yet the true patient population at risk remains poorly characterized. Realizing these concerns, we believe it is reasonable to set a limit on extent of obesity acceptable for our donors until longer follow-up is available. As a conservative measure, we have set an arbitrary limit of BMI < 40 kg/m2 for acceptance of obese donors in our program.

We observed a surprisingly high rate of current or previous smoking in our living kidney donors at 44%. Smoking rates did not differ by BMI group. Although nearly half (20% of our donors) quit smoking prior to their donor evaluation, 24% were active smokers. Prospective kidney donors are advised to quit smoking by the evaluating nephrologist and transplant-hypertension nurse. We have not refused donation solely on the basis of smoking. More likely current smokers were excluded by reduced GFR, hypertension or other factors as demonstrated by a trend to higher smoking rates in those renal donor candidates denied approval. Known risks of accelerated cardiovascular disease and progression of renal disease related to smoking highlight the need for closer attention to this issue.[22,23]

Over the past several years we have accepted select individuals who are obese but otherwise in good health. Our data indicate a spectrum of rising levels of glucose, triglycerides and blood pressure with BMI even while these values remain within normal ranges. More donor candidates were denied approval at higher BMI associated with higher rates of hypertension, and family history of diabetes and cardiovascular disease. Among donors at BMI ≥ 35 kg/m2, only 12 had a BMI above 40 (21% of highest BMI group, 2% of total group) including 3 above 45. Our study presents initial data in selected patients across a wide range of BMI and provides a foundation to establish long-term follow-up of these individuals. These results are unique in that we add a standard return visit at 6-12 months after renal donation providing at least early follow-up including blood pressure, urinary microalbumin and GFR on large numbers of renal donors. This information extends our knowledge beyond the immediate perioperative and post-operative period with demonstrated clinical stability. We believe we have an obligation to closely monitor those wishing to donate at higher risk. For obese donors, follow-up provides the potential for intervention utilizing dietary, exercise and mental health expertise.

Our results support the cautious acceptance of obese donors who meet strict selection criteria and who are highly motivated to donate. The decision to donate a kidney to a family member or friend is an altruistic action, which may lead to improved quality of life for both recipient and donor. While our results regarding the safety of accepting obese individuals as live donors are encouraging, we must re-emphasize that these results involve only short-term follow-up in what we consider a highly select group of obese donors. Within our program, we have arbitrarily set an upper limit on BMI for donor acceptance. We advocate the continued careful study of obese donors and do not support their widespread use until longer follow-up is available.


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