NEW ORLEANS (FRONTLINE MEDICAL NEWS) – If the yardstick for measuring the cost-effectiveness of an operation or a medical treatment is that it costs less than $50,000 for each quality-adjusted life-year gained, then weight-loss surgery as a treatment for type 2 diabetes is cost-effective.

However, more long-term follow-up is needed to determine the true value of metabolic or bariatric surgery such as gastric bypass, compared with medical treatment for type 2 diabetes. Studies of bariatric surgery in the nondiabetic population found it was most cost-effective in the following scenarios: in women; in the morbidly obese vs. the moderately obese; in patients with obesity-related comorbidities including diabetes; when the procedures were performed laparoscopically; and when the studies themselves received industry support.

In people with diabetes, the results were similar. “Diabetes metabolic surgery is more cost-effective early in the course of type 2 diabetes compared to later in the course, when performed laparoscopically, and again when the study received support from industry,” reported Dr. William H. Herman , professor of epidemiology and internal medicine at the University of Michigan School of Public Health in Ann Arbor and director of the Michigan Center for Diabetes Translational Research.

He reviewed 11 economic analyses of bariatric surgery and concluded that all exceeded the benchmark for cost-effectiveness based on the cost per quality-adjusted life-year (QALY) gained. Six studies evaluated the general population of obese people and found that the cost-effectiveness ratios ranged from $1,600 to $44,000 per QALY gained. The remaining five studies involved obese patients with type 2 diabetes, two of which reported cost-effectiveness ratios of $2,000 to $23,000 per QALY gained; and the remaining three studies actually reporting a cost-savings. “In other words, the money spent on these interventions was more than recouped in the savings resulting from reduced downstream medical costs,” Dr. Herman reported at the American Diabetes Association scientific sessions.

The studies that found gastric bypass cost-saving in diabetes are noteworthy, Dr. Herman said. “If an intervention is more effective and less costly than a comparator intervention, then it is cost-saving, and that really is an unusual finding in health or medicine; perhaps 10% or 15% of interventions turn out to be cost-saving,” he said. “These are interventions that we want to adopt and put into practice pretty much without question.”

By the same measure, if an intervention is more costly and less effective, it’s easy to dismiss “out of hand,” Dr. Herman said. However, interpreting some of the studies he evaluated was more nuanced. “The problem occurs when a new treatment is both more effective but more costly, which was the case with two of the five analyses of metabolic surgery, and all of the analysis of bariatric surgery in the nondiabetic population,” he said

While gastric bypass surgery for type 2 diabetes is a good value, Dr. Herman added a few caveats. “When one looks at other interventions in similar categories, metformin for diabetes prevention has recently been shown to be cost-saving,” he said. He also said surgery is more cost-effective than marginally cost-effective interventions like intensive glycemic management for people with newly diagnosed type 2 diabetes or retinal screening every year vs. every 2 years.

One key issue with the existing evidence on cost-effectiveness of metabolic surgery for type 2 diabetes that Dr. Herman elucidated is how the studies accounted for participants lost to follow-up. “We know that a patient lost to follow-up may have a less favorable outcome than one who returns for follow-up,” he said. There are two ways studies can account for lost patients: the available-case analysis, which assumes that the patients lost to follow-up have the same rates of remission; and the attrition-adjusted available case follow-up, which uses a worst-case imputation. “I would argue that to account for attrition bias, remission rates calculated using the cases available for follow-up should be adjusted using worst-case imputation,” Dr. Herman said.

He pointed out another limitation when calculating the value of gastric bypass surgery for type 2 diabetes: “There are no randomized clinical trials of metabolic surgery that describe its long-term impact on diabetes treatments, complications, comorbidities, and survival. And it really is going be very important to get these data to confirm the cost-effectiveness of metabolic surgery.”

Among the shortcomings of the existing literature he noted are the assumptions that treatment-related adverse events are self-limited, that body mass index (BMI) achieved up to 5 years after surgery will remain stable, and that diabetes will not relapse. “The data are pretty good now on reversal, remission, hernia repair, and those sorts of things, but we need to look at longer downstream costs associated with surgery, including the need for cholecystectomy, joint replacements, and nutritional deficiencies that may occur and do clearly have financial implications,” he said.

At the same time, the analyses on gastric bypass surgery for type 2 diabetes could be more favorable if they account for improvements in health-related quality-of-life and rely less on cross-sectional data. Dr. Herman said, “I would argue that using cross-sectional data to estimate changes in health-related quality of life as a function of BMI underestimates the improvements on health-related quality-of-life associated with weight loss and will in fact underestimate the cost utility of interventions for obesity treatment,” he said.

Dr. Herman added, “Clearly the evidence to date suggests that metabolic surgery is cost-effective, but I’ll be more assured when I see longer-term follow-up.”

Dr. Herman has no financial relationships to disclose.