To lose or not to lose?
Sticking with the heavy issue of weight and PKD, I am pondering the requirement to trim my BMI, purely with respect to increasing my chances of getting a transplant when the time comes.
It is known that a population of patients with chronic kidney disease will have a higher incidence of obesity than the general population. There is undoubtedly obesity-related co-morbidity. But is it fair to use BMI to restrict access to renal transplant? Below I have considered whether using BMI to select candidates for renal transplant is based on medical evidence.
In the 1990s, of those patients on the renal transplant waiting list (US) about 20% were classified as obese with a BMI above 30. By the year 2015 this figure had risen to more than 35% and some 10% fell into the morbidly obese category, BMI greater than 35. Defining morbid obesity has varied by nation and era, but generally it can be considered as a BMI between 35 and 45.
Arguments for retaining BMI as a gateway to transplant include both medical and financial outcomes.
The cynical side of me would suggest that financial reasoning has dominated in this area. Transplant programs will be graded by performance that covers duration of hospital stay – even one or two extra days added to the average in-patient stay can add $20,000 onto the costs. There are therefore very strong financial disincentives for transplanting obese patients. These rarely factor-in the reduced costs comparing transplant with a lifetime on dialysis.
The majority of treatment centres restrict transplants based on BMI. This is a worldwide situation. One international study revealed that 29% centres had a BMI-cutoff of 35 and a further 27% were even more strict with a cutoff of BMI 30. A similar number of centres still used BMI to allocate organs but do not have a specific BMI above which they refuse – they do at least make individual decisions rather than having a blanket policy.
However, as we have discussed before, BMI does not assess the distribution of fat, the degree of lean muscle mass or the person’s nutritional state.
The dictat to lose weight before transplant carries the implicit assumptions that BMI is modifiable and that weight loss will have a positive impact on the outcome. Both could be reasonably questioned.
If any area needs more data to enable evidence-based advice then this one does. Gathering data is problematical because bias has already been introduced by refusal to transplant the morbidly obese. Some centres just never list obese patients, while others place them on the “inactive list” while they are attempting to lose weight. There is also a suggestion of provider/gender bias as some centres have a cutoff-BMI of 35 for women but 40 for men
What are the outcomes that may be affected by weight?
The immediate ones which are most concerning for the patient include delayed graft function, meaning the new kidney is slow to respond or “wake-up” and higher rates of wound infection with an associated slow wound healing. These in turn will likely lead to longer periods as an inpatient, which are the factors most concerning to the insurance companies or the NHS funds.
These data are relatively easy to obtain and I will not dispute that there is an increased risk for the patient with larger BMI who receives a transplant when compared to a non-obese patient receiving a transplant. But I would question whether this is the comparison we should be making – from the patient perspective the more pertinent comparison is not “fat or thin” but that of “transplant or no transplant”.
One important outcome is graft survival – how long is your new kidney going to keep working? Here the data that exists is contradictory with some studies indicating shorter survival for obese patients and some showing no effect. In part this will depend on what statistics are used to analyse the data and what the studies are designed to test. I am not saying this isn’t an important issue, it certainly is, but the available data has already been attenuated by the exclusion of obese patients from transplant programmes so the validity of using this data to draw conclusions has to be questioned.
The strongest argument against using BMI for transplant allocation is derived from comparing the outcomes for obese people on dialysis with obese people who have transplants. This, after all, is the actual scenario faced by an obese person with kidney failure. Here there is very clear evidence that those people with BMI between 30 and 40 will do better with a transplant than on long term dialysis. This survival advantage is still demonstrable for people older than 50 yrs and for those who also have type 2 diabetes. If the BMI is over 41 then the outcomes are less clear cut, so this is an area requiring determination by individual circumstances.
The next piece of evidence we should consider is the outcomes of weight loss in patients with end stage renal failure – multiple studies have shown higher risk for those on dialysis who lose weight and where there is significant weight loss prior to transplant then it tends to be transitory, the patients gain weight quite soon after the transplant. However, none of these papers take into account whether the weight loss is intentional or incidental.
Is intentional weight loss achievable whilst on dialysis?
Many patients at end stage renal failure will find it hard to exercise due to fatigue, anaemia, medication or just from the volume changes involved with dialysis. So maintaining muscle mass while on dialysis is hard.
Serum albumin can be used as a marker of nutritional status in dialysis patients. Using this measure, it is accepted that protein-energy wasting is associated with a poor outcome for dialysis. In those patients with low albumin they almost always need to gain weight in order to raise their levels and improve their nutritional status.
It is frustrating that many transplant centres use BMI to limit access to transplants. They will more often that not accept patients with other comorbidities that carry just as much risk – for example diabetes, sickle-cell anaemia, hepatitis-C.
It feels as if it is a social stigma that results in obesity being treated differently.
Weight loss is often NOT achievable and when it is achieved then it is often transient. In my mind this amounts to discrimination rather than evidence-based practice.
Note: Bias is entirely probable since I am rather plump.