Uninsured Americans tend to be discharged from the hospital somewhat sooner than those with health coverage, regardless of the medical condition itself, a new study finds.

Researchers are not sure what the reasons for the findings are. And it's not clear that a shorter hospital stay is a bad thing.

Still, the findings suggest that financial factors are playing a role in hospital length of stay, the authors say.

Looking at records for nearly 850,000 adults discharged from U.S. hospitals between 2003 and 2007, the researchers found that uninsured patients had a slightly shorter stay than patients with private insurance or Medicaid -- the government-funded health program for the poor.

When it came to potentially preventable hospitalizations -- for worsening of chronic health problems like asthma or diabetes, for example -- uninsured patients stayed in the hospital just under 2.8 days, on average.

That compared with 2.9 days for patients with insurance and 3.2 days for Medicaid patients.

The gap sounds small, but it's still meaningful, according to lead author Arch G. Mainous III, of the University of South Carolina, Charleston.

"Does this represent something? I think it does," he told Reuters Health.

The difference in hospital length-of-stay was apparent even though the researchers accounted for age, race, sex and the number of medical conditions patients had.

And if anything, Mainous said, it would make sense for uninsured patients to be in worse shape when they arrived at the hospital for a chronic health condition -- since they would be less likely to have routine health care to manage the problem.

"So why would they have a shorter hospital stay?" Mainous said.

In addition, the researchers found that uninsured patients also had shorter stays when they were treated for problems not related to everyday healthcare -- like a traumatic injury.

All of that said, it's not possible to tell whether the shorter hospital stays are "necessarily bad," Mainous said.

The findings are based on a national sampling of hospital discharge records. And the researchers had no way of finding out how patients fared after their discharge -- including whether uninsured people faced a greater risk of readmission.

Mainous said there are two possibilities. One is that uninsured patients are more likely to be discharged from the hospital "prematurely." Another is that patients with insurance are sometimes kept longer than necessary because their payment is covered.

"We can't really say which it is right now," Mainous said. But he added that the findings do suggest that financial considerations are playing some role.

Mainous noted that Medicaid patients actually had the longest hospital stays, so "it's not just something about being poor" that explains the shorter hospital stay among uninsured people.

The researchers also excluded records from patients who left the hospital against doctors' advice -- which is more common among people who lack insurance. So that doesn't explain the findings either, Mainous said.

Finding out exactly why uninsured patients leave the hospital sooner, and what the potential effects might be, is no easy task. It's possible to track medical records for patients who are part of a large health plan, or on Medicaid.

But there are no large databases that track Americans without health coverage, Mainous pointed out.

The number of uninsured Americans stood at almost 50 million last year, inching up from the year before.

With that rising number, Mainous said, it will be increasingly important to find out how insurance status is affecting people's hospital stays.