Do we need to worry about weight and transplantation?

NOTE: This article was first published in May 2021 in Issue 13 of our Kidney Matters magazine

As part of my medical school studies, I spent six months working on a research project exploring the issue of obesity in kidney transplantation, under the supervision of transplant physician Dr Paul Phelan. This area of research is of great interest, as previous studies conducted in the UK have suggested that obese patients are at a greater risk of complications and poor outcomes after their transplant. Examples of poor outcomes include the kidney transplant not functioning well or the patient developing new-onset diabetes after their transplant. Furthermore, some researchers believe that patients who gain a significant amount of weight following their transplant may also have an increased risk of health problems.

However, there is continuing debate about the precise impact on patient outcomes of obesity at transplant or weight gain after transplant. This is reflected in differences both internationally and at a local level in how the issue is dealt with. Some transplant centres use a ‘cut off’ whereby patients must have a BMI (body mass index) below a certain level before they can be eligible for a transplant. This topic is very contentious, especially considering many patients on dialysis find it difficult to manage their weight due to factors out of their control.

The primary component of our project consisted of analysing data from all patients who underwent kidney transplantation at the East of Scotland Renal Transplant Centre during 2015 and 2016. This included 205 patients, six in 10 (59%) of whom were male. We also created an online survey, which we distributed to NHS Scotland clinicians who are involved kidney transplantation. Respondents included 22 physicians, four surgeons, eight specialist trainees, 10 dieticians and 11 nurses and transplant co-ordinators.

Key findings from the study

• Clinicians across NHS feel that weight management resources for kidney transplant candidates and recipients are lacking
• Mean (average) weight gain one year after kidney transplant is 3.0kg (7 lb)
• Compared to healthy weight, obesity at transplant may be associated with a greater risk of developing diabetes and having worse kidney function after transplantation.

Obesity and outcomes

Before discussing results, it is important to note that all research should be treated with caution. Our conclusions are valid for the group of patients we studied, but may not necessarily be true for everyone. Furthermore, the work has not been peer reviewed (i.e. evaluated by our colleagues working in this area of research).

We found no association between patient BMI classification (see Figure) and length of hospital stay, readmission to hospital within 90 days of transplant or delayed graft function (when the kidney does not function immediately after the transplant). However, when patient BMI was plotted against eGFR at one and two years post-transplant, we found a weak, but significant negative correlation. This suggests that the more overweight the patient, the lower the function of their new kidney at one and two years after their transplant. There was also an association between BMI category and new-onset diabetes within the first year post-transplant, in that the higher the BMI, the greater the risk of developing diabetes.

After the transplant

We also found that many patients’ bodyweight changed during the first year post-transplant, the mean weight change being an increase of 3 kg (7 lb). With further analysis we found that this meant that over one third (35.5%) of ‘healthy’ or ‘underweight’ patients became ‘overweight’ and less than one third (30.6%) of patients who were initially ‘overweight’ became ‘obese’ by the end of this period. However, minorities of patients in each BMI category lost weight, with one in 10 (11.1%) ‘overweight’ patients moving down to ‘healthy’ or ‘underweight’ and one in seven (14.8%) ‘obese’ patients moving to ‘overweight’.

Finally our survey revealed that over half (58%) of clinician respondents did not think that obesity ‘cut off’ criteria should be used as a criterion for wait listing. Respondents were also generally unhappy with the current weight management resources available for kidney transplant patients. More than four in five (80%) rated their ‘accessibility’ and ‘effectiveness’ as ‘okay’ or ‘poor’.

As you can see, our study suggests that obesity at transplant may have negative effects on patient outcomes. However, in many domains no significant difference could be found. It is clear that improvements could be made in how we deal with the issue of weight management in kidney transplant patients. Further investigation into why some patients lose weight post-transplant when the majority appear to gain weight would be beneficial. As would an assessment of the potentially positive effects of weight loss.

I conducted this project at the Royal Infirmary of Edinburgh, as part of my studies at the University of Edinburgh. I was helped in all aspects of the project by my supervisor, Dr Paul Phelan. Dr Tineke Rennie kindly shared her previous work on this topic. I was also assisted by Gillian Walker, Dr Margaret MacDougall, and Dr Bernadine Chua.