The death rate in people suffering from the chronic auto-immune disease lupus varies among different races and ethnic groups, a study indicated.

Previous research had shown that in the United States nonwhites were at higher risk of having lupus, but it had been uncertain whether that was linked to a higher mortality rate as well.

The study involving data recorded on 42,200 lupus patients between 2000 and 2006 found significant variations in those rates, the researchers reported in the journal Arthritis & Rheumatology.

Of that group, 40 percent were black, 38 percent white, 15 percent Asian and 2 percent Native American.

The annual mortality rate per 1,000 person-years was highest in Native Americans at 27.52, followed by Blacks at 24.13 and Whites at 20.17.

The lowest mortality rates were found in Hispanic and Asian lupus sufferers in the study.

The lower rate in Hispanics came as a surprise, the researchers said, since some previous studies had suggested the opposite.

However, those studies may have been limited to only the most severe cases, seen in an academic setting.

The latest study used data in Medicaid claims filed by patients in 47 states and Washington, D.C., who ranged in age from 18 to 65.

"While previous research has examined racial differences among lupus patients, the studies have primarily been based at academic research centers," says lead author Dr. Jose Gomez-Puerta of Brigham and Women's Hospital in Boston. "Our study investigates the variation in death rates due to lupus among different ethnic groups in a general clinical setting."

Lupus is a chronic disease in which the body's autoimmune system, meant to fight off germs, viruses and bacteria cannot tell the difference between those "foreign" invaders and the body's own healthy tissues.

That results in the immune system creating autoantibodies that attack and destroy healthy tissues, causing pain, inflammation and damage in skin, joints or organs.

An estimated 1.5 million people in the United States suffer from lupus, according to figures provided by the Lupus Foundation of America.

The findings of varying death grates among different groups could lead to new understanding of the disease, the researchers say.

"In less than three years of follow-up of Medicaid patients with lupus, we found a great disparity in mortality rates among ethnic groups," Gomez-Puerta says. "Understanding the variation of death among the races is important to determine how best to treat individual patients, modify risk factors, and ultimately improve survival for those with lupus."