Previous studies found that black patients fared poorly after transplants compared to whites, but less was known about how different racial groups do while they are waiting for a donor organ.

"The knowledge of disparity is usually the first step in ultimately getting rid of it," said Tajinder Singh from Boston Children's Hospital, who led the study that appeared in the journal Circulation.

Singh and his team gathered data from the U.S. Organ Procurement and Transplantation Network, which maintains the wait list for patients needing an organ.

More than 10,000 people were added to the list to receive a heart between July 2006 and September 2010.

Singh's group found that 10.5 percent of white patients who were listed died during the study period or were taken off the list because they were too sick to receive a donor heart.

In comparison, 11.6 percent of black patients and 13.4 percent of Hispanic patients died or were removed from the list.

"All of us have recognized that ethnicity and race play a role in outcomes," said Ashish Shah, a transplant surgeon at Johns Hopkins Hospital in Baltimore, who was not involved in the study, adding that it was not clear what caused the disparities.

Black and Hispanic patients tended to be sicker by the time they were placed on the wait list, the study said.

For instance, 69 percent of black patients and 65 percent of Hispanics were considered to be of the highest urgency for a transplant, compared to 54 percent of white patients.

When the researchers took into account how sick people were, they found Hispanics were 51 percent more likely to die on the wait list than whites.

Health insurance, education levels and income can make a difference in people's health and chance of dying, and Singh's group tried to factor these in as well.

Still, researchers said it's possible to miss important factors that might explain the differences, including certain other measures of sickness.

If the Hispanic patients are just as sick as white patients but are still more likely to die while on the wait list, then something else must be going on, Shah said.

"Are therapies in particular racial groups less effective?" he added.

The researchers also found that blacks were more likely to die in the hospital after receiving a heart than whites.

Among more than 6,000 patients, 5.4 percent of white patients, 5.9 percent of black patients and 3.9 percent of Hispanic patients died in the hospital. SOURCE: bit.ly/JTipoR

(Reporting from New York by Kerry Grens at Reuters Health; editing by Elaine Lies and Bob Tourtellotte)

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