Patients have better weight loss surgery outcomes in accredited centers, a review of past studies has found. Researchers analyzed 13 studies with a combined 1.5 million participants that examined the differences in deaths and major complications at accredited versus non-accredited centers.

The studies suggest that costs are lower, and the quality of patients’ experiences is better, at hospitals with accreditation for bariatric surgery.

Accreditation means the hospital has passed a rigorous review process during which it proved that it can maintain certain physical resources, staffing resources, and standards of care.

“Deciding which provider to pick for surgery can be daunting. With so many different rankings out there, it’s hard to figure out what makes a real difference,” study author Dr. John Morton, chief of bariatric and minimally invasive surgery at Stanford School of Medicine in Palo Alto, California, told Reuters Health. “Evidence shows that accreditation does make a difference.”

Morton and colleagues report in the Journal of the American College of Surgeons that in 10 of the 13 studies, accreditation made a significant difference. Six of the eight studies that reported mortality showed a significant reduction at the accredited centers; the risk of death was two to three times higher at hospitals that weren’t accredited.

Eight of 11 studies showed a reduction in major complications, the researchers found.

“While quality and safety of bariatric surgery has improved across the board over the last 10 years, accreditation programs provide the structure, data collection and oversight for quality improvement and assessment of patient outcomes,” said Dr. Stacy Brethauer, a laparoscopic and bariatric surgeon at the Cleveland Clinic in Ohio, who wasn’t involved in the study.

The review comes at a time when weight loss surgery accreditation is under scrutiny nationally. Surgical weight loss has gained in popularity, with more than 180,000 procedures done annually in the U.S., according to the American Society for Metabolic and Bariatric Surgery (ASMBS).

In response to the growth, ASMBS and the American College of Surgeons created accreditation programs in 2004 and 2005. In 2013, the two nationwide programs merged to create the Metabolic Bariatric Surgery and Quality Improvement Program.

Most insurers still require accreditation for reimbursement, but “the glaring exception is Medicare,” said Morton, also immediate past president of ASMBS.

For several years, the Centers for Medicare and Medicaid Services did require hospitals to be accredited, but it no longer does.

“Maybe that should be reexamined, especially because Medicare patients are some of our highest-risk patients who could benefit even more,” Morton said.

Accreditation for bariatric surgery benefits other hospital departments, too, Morton noted. Required resources – such as specialized exam tables and chairs – help accommodate obese patients hospitalized for other reasons, he said.

“Accredited centers also have the multidisciplinary team, with experts in psychology and nutrition, for example, to better take care of patients after surgery,” Morton said. “It’s the whole culture, frankly.”

Most of the studies spanned the years 2002 to 2011, when centers were increasing the use of less invasive laparoscopy and gastric banding, which likely improved outcomes. In addition, researchers lacked data on patients’ risk factors, such as their body mass index or how sick they were at the time of surgery.

Also, the authors point out, accreditation itself may not directly improve outcomes, but rather the surgeon quality or institution volume associated with accreditation.

“Like any systematic review, the findings are only as good as the studies that are used to comprise it,” Brethauer said by email. “In this case, there are relatively few large studies done by a small number of researchers. Fortunately, the quality of the papers and the number of the patients overall helps to support the findings.”

As the demand for bariatric surgery grows, patients should research their surgeons and surgery centers before making critical decisions about an operation, said Dr. Samer Mattar, chief of the bariatric services program at Oregon Health and Science University in Portland.

“Accredited institutions provide a higher quality of care,” said Mattar, who wasn’t involved in the study. “This confirms that it’s not a coincidence or fluke. It’s a reality.”