Patients who lack health insurance are more likely to die from car accidents and other traumatic injuries than people who belong to a health plan -- even though emergency rooms are required to care for all comers regardless of ability to pay, according to a study published today.

An analysis of 687,091 patients who visited trauma centers nationwide from 2002 to 2006 found that the odds of dying from injuries were almost twice as high for the uninsured than for patients with private insurance, researchers reported in Archives of Surgery.

Trauma physicians said they were surprised by the findings, even though a slew of studies had previously documented the ill effects of going without health coverage. Uninsured patients are less likely to be screened for certain cancers or to be admitted to specialty hospitals for procedures such as heart bypass surgery. Overall, about 18,000 deaths each year have been traced to a lack of health insurance.

But insurance status isn’t supposed to be a factor for trauma patients. The Emergency Medical Treatment and Active Labor Act, passed by Congress in 1986, guarantees that people brought to emergency rooms get all necessary treatment no matter what kind of insurance they do -- or don’t -- have.

The research team from Harvard University and Brigham and Women’s Hospital in Boston used information from 1,154 U.S. hospitals that contribute to the National Trauma Data Bank. The team found that patients enrolled in commercial health plans, health maintenance organizations or Medicaid had an equal risk of death from traumatic injuries when the patients’ age, gender, race and severity of injury were taken into account.

The risk of death was 56% higher for patients covered by Medicare, perhaps because the government health plan includes many people with long-term disabilities, said Dr. Heather Rosen, who led the study while she was a research fellow at Harvard Medical School.

The risk of death was 80% higher for patients without any insurance, the report said.

The researchers also did a separate analysis of 209,702 trauma patients ages 18 to 30 because they were less likely to have chronic health conditions that might complicate recovery. Among these younger patients, the risk of death was 89% higher for the uninsured, the study found.

Rosen, now a surgical resident at USC’s Keck School of Medicine, said the group expected to find at least some disparity based on insurance status. But she said the group was surprised at the magnitude of the gap.

Dr. Frank Zwemer Jr., chief of emergency medicine for the Hunter Holmes McGuire VA Medical Center in Richmond, Va., said he was “kind of shocked.”

“We don’t ask people, ‘What’s your insurance?’ before we decide whether to intubate them or put in a chest tube,” said Zwemer, who wasn’t involved in the research. “That’s not on our radar anywhere.”

The researchers offered several possible explanations for the findings. Despite the federal law, uninsured patients often wait longer to see doctors in emergency rooms and sometimes visit ERs at several hospitals before finding one that will treat them. Other studies show that, once they’re admitted, uninsured patients receive fewer services, such as CT and MRI scans, and are less likely to be transferred to a rehabilitation facility.

Patients without insurance may have higher rates of untreated underlying conditions that make it harder to recover from trauma injuries, the researchers said. They also may be more passive with doctors and nurses because they don’t interact with them as often. All of these factors could influence whether a trauma patient is able to recover.

But the link could also be coincidental, the authors acknowledged. Perhaps the hospitals that have fewer resources at their disposal also happen to see the most uninsured patients, they said.

The types of injuries may differ too, Zwemer said. Gunshot and stabbing victims -- frequently younger people involved in crime -- were much more likely to die from their wounds than other trauma patients tracked in the study. These people are generally uninsured, but the type of injury -- not insurance status -- is the reason for their higher fatality rates, he said.

More research is needed to figure out whether lack of insurance actually harms trauma patients or whether the data simply reflect a correlation, said Dr. A. Brent Eastman, chairman of trauma at Scripps Memorial Hospital in La Jolla.

The issue is particularly relevant as Congress and the Obama administration weigh various measures to reduce the number of uninsured Americans, Eastman wrote in a short critique that accompanied the study.

karen.kaplan@latimes.com