EXPERIMENTAL AND CLINICAL TRANSPLANTATION

Obesity, which has become an increasing problem worldwide, poses a risk for kidney transplant recipients both before and after surgery. In this literature review, we studied the effects of obesity before and after kidney transplant. There are numerous studies and different opinions on the effects of obesity on graft function before and after transplant. Obesity prolongs surgery time and the ischemic process. A large cohort study of 11 836 recipients noted a close association between body mass index and delayed renal transplant and delayed graft function. However, another study found that being overweight or obese before transplant did not have any effects over the medium and long term. A 20-year follow-up study indicated that the first-year body mass index in recipients after renal transplant had a greater effect on graft function and survival than body mass index before transplant. Still, another study found that body mass index had no effects on graft function and survival. In the study, 3-year graft function and mortality rates of morbidly obese people without diabetes, the functional status without dialysis, and living-donor transplant were reported to be much lower than in those with normal weight. In conclusion, there is no consensus on the effects of obesity before and after transplant, and it has been pointed out that more research should be done on this subject.

Key words : Body mass index, Diabetes mellitus, Graft function, Survival

It is known that body mass index (BMI) of kidney transplant recipients has been increasing steadily.^1,2 Obesity is an ongoing problem that is increasing throughout the world. The World Health Organization (WHO) stated that 1.9 billion adults were overweight, whereas 650 million adults were obese.³ Obesity and its related consequences create a great risk for patients before and after kidney transplant. It is known that pretransplant obesity is a predisposing factor in delayed graft function after transplant. Obesity also adversely affects the process of choosing candidates.⁴ It has been indicated that obesity compromises prognosis while affecting graft and long-term results negatively after transplant.^1,2 In this literature review, we studied the effects and importance of obesity during the pretransplant and posttransplant process in kidney transplant recipients.

Materials and Methods

We used the following key words in a search of Ebscohost, PubMed, Google Scholar, and Cinahl database: obesity and kidney/renal transplant, body mass index, and pretransplant/posttransplant weight.

Results and Discussion

Obesity causes increased sympathetic nervous activity, vasoconstriction, and damage to renal perfusion. However, there are several disagreements on the effects of obesity on renal function during the preoperative and postoperative process.

Postoperative obesity has been reported to cause delayed graft function by extending the duration of surgery and the ischemic process.^5,6 A meta-analysis stated that high body mass index (BMI) of recipients before transplant is associated with a high mortality rate.⁷ However, in a retrospective study by Gill and associates that involved 702 456 patients with chronic kidney disease, women with high BMI had a lower rate of transplant.⁸ In another study, Molnar and associates found that, in 11 836 recipients, there was a close association between pretransplant BMI and posttransplant delayed graft function.⁹ In a retrospective monocentric analysis from 2012, BMI of both donors and recipients in deceased-donor renal transplant was clearly the most important factor affecting delayed graft function.¹⁰

Body mass index may increase surgical complications in the early posttransplant process, although graft function is reversible affected.¹¹ A meta-analysis that compared obese versus other patients posttransplant found that patients with obesity had worse results. In this respect, it was highlighted that candidates with BMI > 35 kg/m² and comorbidity and those with BMI > 40 kg/m² must be evaluated carefully before transplant.¹²

Hoogeveen and associates reported that BMI of recipients during the first year after renal transplant had a greater effect on graft function and recovery (survival) rates than pretransplant BMI.⁴ Other studies are available that reveal this relationship.^13,14 In a meta-analysis, low BMI was noted to decrease posttransplant mortality rates while having a positive effect on graft survival.¹⁵ In a retrospective study from Veasey and associates, BMI and functional outcome of patients had no effect on posttransplant complications separately. However, there was a significant increase in surgical complications when 2 of them existed at once.¹⁵

Furriel and associates¹¹ stated that being overweight or obese before transplant had no long-term or medium-term effects after transplant. In a retrospective study that evaluated the effects of morbid obesity on 42 787 renal transplant recipients, patients with morbid obesity had longer duration of hospital stay, although results between groups were not statistically significant.¹⁶ In a study from Pieloch and associates of 30 132 patients, BMI had no effect on graft function and survival.¹⁷

Survival rates of patients who received long-term dialysis treatment before transplant and who had high BMI have been reported to be higher than in other patients.^18-22 In addition, 3-year graft function and mortality rates in patients without diabetes, not receiving dialysis, having positive functional status, who were morbidly obese, and who received transplants from living donors were reported to be much lower than in normal-weight individuals.¹⁷ Another study by Tremblay and associates emphasized that BMI ≥ 40 kg/m² significantly affected graft function and survival rates compared with low BMI.²³ This positive effect is called the “obesity paradox” in the literature.

Studies on the effects of obesity before and after renal transplant have had varied results. There is no clear consensus on the use of BMI in the selection of recipients. The European Renal Best Practice suggested in a guideline published in 2013 that patients with BMI > 30 kg/m² should lose weight before transplant. The guideline also agreed that evidence on the issue is insufficient.²⁴ In another guideline from 2011, obesity was stated to not be a contraindication for transplant; however, candidates with obesity should be evaluated in detail in terms of pretransplant and posttransplant cardiovascular disease.²⁵

There is no consensus regarding the effects of obesity on patients before and after kidney transplant. Comorbid conditions should be considered along with BMI during the process of patient evaluation before and after transplant. Obesity-related studies, which have had different views on the subject, reveal the necessity of further research.

Volume: 16 Issue: 1 March 2018 - Supplement - 1

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