A group of researchers claim that hospital accreditation is not necessarily tied to better outcomes for U.S. patients.

Based on records for more than 4.2 million patients over age 65 covered by Medicare, the study team found no difference between accredited and unaccredited hospitals in patient death rates, and only a slightly lower rate of patient readmissions at accredited hospitals, according to the report published in The British Medical Journal.

To be reimbursed for care provided to Medicare patients, hospitals either need to be accredited by an independent organization approved by the Centers for Medicare and Medicaid Services, or they must have passed a review by a state survey agency.

To see if accredited hospitals offer better quality care, researchers analyzed data from 4,400 U.S. hospitals, including 3,337 accredited facilities and 1,063 that passed state-based review in 2014-2017. They linked this data with Medicare files and with results of government-sponsored patient satisfaction surveys for all the hospitals.

Overall, they found that patients treated at accredited hospitals had slightly lower 30-day mortality than those at hospitals reviewed by a state agency (10.2 percent versus 10.6 percent), although the difference was too small to rule out the possibility it was due to chance.

The research team also found identical mortality rates (2.4 percent) and nearly identical readmission rates (15.9 percent versus 15.6 percent) for six types of major surgery at accredited and state-reviewed hospitals.

For the medical conditions, readmissions were lower at accredited hospitals, at 22.4 percent versus 23.2 percent, a statistically meaningful difference.

Patient experience scores were slightly higher at state-survey hospitals than at accredited hospitals.

In addition, the research team found no differences in mortality, readmission rates or patient experience scores between the hospitals accredited by The Joint Commission, considered the “gold standard” for accreditation, or other independent organizations, the study team notes.

Future studies should look at what type of accreditation and by which organization seem most helpful for better patient outcomes. For instance, hospitals designated as stroke centers or rehabilitation centers may have better outcomes for particular medical conditions, said Laura Wagner of the University of California, San Francisco, who wasn’t involved in the study.

“The bottom line is that accreditation does matter, and it provides a framework for both patients and healthcare providers around quality,” One of the authors said. “It can improve quality in some cases, and we need to improve that framework to provide care.”