March 2017 Cover, AJKD, © National Kidney Foundation.

Today is World Kidney Day, a global campaign aimed at raising awareness about kidney health. The theme for 2017 is a focus on “Kidney Disease and Obesity.” The official editorial focuses on the association of obesity with chronic kidney disease (CKD) and the proposed mechanisms of action (inflammation, oxidative stress, lipid metabolism, insulin resistance, etc.) underlying this worldwide epidemic.

A recent AJKD article by Imam et al that coincides with this theme explores the use of weight loss surgery to slow or prevent deterioration of kidney function. Operations such as Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy have examined obesity outcomes, including deterioration of kidney function. The authors hypothesized that bariatric surgery would be associated with improvement in eGFR when compared to nonsurgery controls and performed an observational retrospective cohort study to test this.

The patient population all came from the Kaiser Permanente health system in Southern California. To be eligible, patients were required to have:

• RYGB or sleeve gastrectomy between 2008-2012
• BMI > 30 kg/m²
• eGFR 11-59 ml/min (estimated using CKD-EPI equation)

Nonsurgical controls were patients with the same BMI and eGFR measurements that were referred for surgery during the same time period but did not undergo a bariatric procedure. In total, 714 patients from each group were included in the propensity match analysis. In both groups, the mean weight was 270 lbs, mean BMI was 44 kg/m², and mean eGFR was 48 ml/min. The figure below demonstrates 3 year outcomes for eGFR between the surgery and control groups.

Fig 2B from Imam TH et al, AJKD, © National Kidney Foundation.

What may be surprising to many is that at 3 months post-surgery, the mean eGFR of patients who had bariatric surgery increased from 48 ml/min to 63.2 ml/min. This apparent increase in kidney function was maintained throughout the 3 year period. However, it should be noted that measuring GFR in very obese persons is somewhat controversial, and that GFR values need to be factored for body surface area. When the two surgeries were compared in this study, weight loss and improvement in eGFR was better in patients who underwent RYGB as compared to sleeve gastrectomy (see figure below).

Fig 3A and 3B from Imam TH et al, AJKD, © National Kidney Foundation.

With a projected increase in obesity-related kidney disease expected in the coming decades, these surgical options provide some hope not only to delay progression, but to actually improve eGFR! Despite its observational study design, this paper hopefully sets the stage for future randomized controlled trials which may lead to more definitive recommendations. For now, though, practitioners with access to a bariatric surgery center can consider referrals for surgery not only for the benefit of losing weight, but also to potentially benefit kidney health. After all, raising awareness of kidney health is the purpose of this global campaign.

Happy World Kidney Day!

Post prepared by Timothy Yau, AJKD Social Media Editor

To view the Imam et al article abstract or full-text (subscription required), please visit AJKD.org.