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We’re supposed to be more proactive about our health, and engage in making decisions that can impact our care. But what if that decision-sharing just adds to our medical bills?

A team of researchers from the University of Chicago School of Medicine were surprised to discover just that — patients who were more involved in their medical care decisions spent 5% more time in the hospital and tallied up hospital costs that were $865 on average more than what less involved patients spent.

According to the study authors, shared decision-making between doctors and patients is an important part of improving care, but based on their results, the greater involvement may not always be associated with lower costs.

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To assess how big a role patients preferred to play in working with their doctors, the researchers offered a survey to those admitted to the University of Chicago’s general internal medicine service between July 2003 and August 2011. By the end of the study period, 21,754 patients had answered questions about how much information they wanted about their conditions or how much they agreed with the statement, “I prefer to leave decisions about my medical care up to my doctor.” The researchers compared these responses to the patients records.

Most wanted information about their care options, but only 28.9% wanted to play a greater role in deciding what type of care they needed. The patients who did not prefer to leave decisions solely up to their doctor spent more time in the hospital and had 6% higher costs.

Given that about 35 million people are hospitalized every year in the U.S., and about 30% of patients get involved in their medical decision making, the researchers calculated that the practice could lead to $8.7 billion in additional health care costs annually.

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What drives up those costs? Part of the added expense could come from patients who, because they are more involved in their care, may spend more time in hospitals and utilize more resources such as tests or lab facilities. With patients who ask more questions about their care and share in deciding which tests to have, doctors may also be inclined to perform or order interventions simply to appease patients or avoid malpractice litigation.

The higher costs, however, need to be balanced with the potentially higher quality care and greater satisfaction that patients generally report when they are more engaged in their own care. That’s why the researchers were concerned by the fact that their results also showed a disparity in which patients were asking to be more involved in their care. Older, less educated, and publicly insured participants were less likely to be engaged in medical decision making, and such differences could lead to disparities in the quality of care they receive, as well as their satisfaction with their health.

“We need to think harder and learn more about what it means to empower patients in multiple health care settings and how incentives facing both patients and caregivers in those settings can influence decisions,” said study author Dr. David Meltzer, an associate professor of medicine, economics and public policy at the University of Chicago in a statement.

The study is published in JAMA Internal Medicine.