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Microvascular Outcomes in Patients With Diabetes After Bariatric Surgery

IN RESPONSE: Dr. Carlsson and colleagues are correct that the SOS study did examine retinopathy independent of other microvascular outcomes. We reviewed and referenced their 2014 article but not their article published in 2017. We also agree that whether diabetes duration is a potential effect modifier is an important question. The analysis that Dr. Carlsson and colleagues performed in their 2017 article, which stratified analyses of microvascular outcomes by baseline glycemic status, evaluates a similar question. Overall, we agree that their results suggest that patients with earlier-stage diabetes may benefit more from bariatric surgery than those with later-stage disease. This finding is consistent with those from our prior publication suggesting that a shorter duration of diabetes is associated with an increased likelihood of and longer duration of diabetes remission, which may be related to decreased microvascular complications (1). Although we did not conduct the analysis that Dr. Carlsson and colleagues propose, we hope to address this question in a future article. Drs. Kwon and Park correctly note that panel G of Figure 2 of our article shows that the risk for nephropathy in the surgery group significantly increased immediately after bariatric surgery compared with that in the control group (on the basis of shaded 95% CIs). This small increase in postoperative risk for nephropathy did not substantially affect the long-term cumulative incidence of nephropathy (see panel C of Figure 2 of our article). Table 2 of our article shows that the overall cumulative incidence rates of nephropathy were similar among surgical and nonsurgical patients (2.7% and 2.8%, respectively) at the end of year 1 and that rates of incident nephropathy at 3, 5, and 7 years were 3.6%, 4.9% and 6.4%, respectively, after bariatric surgery compared with 6.8%, 10% and 14%, respectively, among nonsurgical patients. This finding suggests that any potential early negative effect of bariatric surgery on renal function is small compared with its long-term potential benefits on the risk for nephropathy among patients with diabetes. Because our study focused primarily on long-term end points, we did not discuss the evidence that early postoperative incidence of nephropathy increased after bariatric surgery. Whether this finding is due to worsening diabetic nephropathy or other renal injury is unclear, because we did not evaluate data looking for potential explanations (such as admissions for postoperative dehydration, use of nephrotoxic medications to treat infections, and use of contrast for imaging studies). Approximately 13% of patients who have major abdominal surgery (range across studies, 3% to 35%) develop acute kidney injury (2, 3), although rates after bariatric surgery may be lower at 5% to 10% (3, 4). We are not aware of any bariatric-specific risks for acute kidney injury. Nevertheless, there are gaps in the understanding of the incidence and risk factors for deterioration in renal function in patients after bariatric surgery, and we welcome future studies in this area.