The effect of obesity on kidney transplant outcomes

Research recently published in BMC Medicine raises a recurring question: should obese patients with end stage renal disease be required to lose weight before being offered a kidney transplant? In this guest post, Dr Iain MacPhee discusses the findings.

End stage renal disease (ESRD) is an increasingly common problem where failure of the kidneys results in patients requiring renal replacement therapy in the form of dialysis or a kidney transplant. In the UK, 888 out of every million people are on renal replacement therapy.

The best treatment for ESRD is a kidney transplant from a living donor (if available) or from a deceased organ donor. Transplantation not only improves quality and quantity of life but is extremely cost effective when compared to long-term dialysis. The key issue addressed by this new BMC Medicine paper is whether obesity should be regarded as a barrier to kidney transplantation.

As with the general population, an increasing proportion of the renal replacement population is obese. Indeed, obesity increases the risk of developing kidney disease. One of the consequences of increasing obesity is an epidemic of type 2 (adult onset) diabetes mellitus. Diabetic kidney disease is now one of the commonest causes of ESRD.

The metabolic syndrome which accompanies obesity, causing hypertension and hyperlipidaemia, increases the risk of cardiovascular disease. Hypertension can cause or accelerate the progression of damage to kidneys and atherosclerosis (damage to blood vessels through deposition of cholesterol) can affect all organs including the kidneys.

Obesity has traditionally been regarded as a barrier to transplantation on the grounds of increased incidence of surgical complications and perceived poorer long-term outcomes.

This new meta-analysis included over 209,000 renal transplant recipients from studies where transplant outcomes were compared between patients with body mass index greater or less than 30 kg/m2. While there was a clear increase in early surgical complications and metabolic problems, in particular new onset diabetes after transplantation (NODAT), there was remarkably little impact on three-year patient and transplant survival.

The traditional approach in the UK has been to hold off transplantation until obese patients achieve a target weight with body mass index less than 30 kg/m2 with some leeway for patients with body mass of up to 35 kg/m2, as advocated by the authors of this meta-analysis.   However, we all know that weight loss is challenging and even if patients lose weight to allow transplantation, there is a tendency to gain it all back again after the surgery.

A utility argument can be applied given the inadequate supply of deceased donor organs that these should be allocated to patients with the best long-term outcomes

A key current controversy is whether obese patients should be denied the potential benefits of transplantation based on current evidence of poorer outcomes when compared to non-obese individuals, but possibly better outcomes for these individuals than they would have on long-term dialysis. Bariatric surgery is seeing increasing use but the surgical complication rate is probably higher in patients with ESRD. Is it reasonable to insist on such an invasive approach to weight loss as a condition for renal transplantation?

A utility argument can be applied given the inadequate supply of deceased donor organs that these should be allocated to patients with the best long-term outcomes, although this does not apply in the case of live donation.

Based on the current data, a number of other factors, in particular cardiovascular comorbidity probably have a bigger impact on survival than obesity. It is probably reasonable that practice is drifting towards transplanting more obese patients. This needs to be accompanied by careful collection of outcome data, in particular for patients with BMI >35 kg/m2 to ensure that transplantation is, in fact, in their best interests.

We are unlikely to see any sufficiently powered randomised controlled trials of renal transplantation in the obese and will need to rely on registry data.

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